diff --git a/src/@types/common.ts b/src/@types/common.ts
new file mode 100644
index 00000000000..6868d766008
--- /dev/null
+++ b/src/@types/common.ts
@@ -0,0 +1,3 @@
+import BattleScene from "#app/battle-scene.js";
+
+export type ConditionFn = (scene: BattleScene, args?: any[]) => boolean;
diff --git a/src/account.ts b/src/account.ts
index 7fd1d208496..6682e3e0b7c 100644
--- a/src/account.ts
+++ b/src/account.ts
@@ -8,7 +8,7 @@ export interface UserInfo {
   googleId: string;
 }
 
-export let loggedInUser: UserInfo = null;
+export let loggedInUser: UserInfo | null = null;
 // This is a random string that is used to identify the client session - unique per session (tab or window) so that the game will only save on the one that the server is expecting
 export const clientSessionId = Utils.randomString(32);
 
@@ -30,11 +30,13 @@ export function updateUserInfo(): Promise<[boolean, integer]> {
       loggedInUser.lastSessionSlot = lastSessionSlot;
       // Migrate old data from before the username was appended
       [ "data", "sessionData", "sessionData1", "sessionData2", "sessionData3", "sessionData4" ].map(d => {
-        if (localStorage.hasOwnProperty(d)) {
-          if (localStorage.hasOwnProperty(`${d}_${loggedInUser.username}`)) {
-            localStorage.setItem(`${d}_${loggedInUser.username}_bak`, localStorage.getItem(`${d}_${loggedInUser.username}`));
+        const lsItem = localStorage.getItem(d);
+        if (lsItem && !!loggedInUser?.username) {
+          const lsUserItem = localStorage.getItem(`${d}_${loggedInUser.username}`);
+          if (lsUserItem) {
+            localStorage.setItem(`${d}_${loggedInUser.username}_bak`, lsUserItem);
           }
-          localStorage.setItem(`${d}_${loggedInUser.username}`, localStorage.getItem(d));
+          localStorage.setItem(`${d}_${loggedInUser.username}`, lsItem);
           localStorage.removeItem(d);
         }
       });
diff --git a/src/battle-scene.ts b/src/battle-scene.ts
index f54ff92e324..4269edecfaf 100644
--- a/src/battle-scene.ts
+++ b/src/battle-scene.ts
@@ -106,8 +106,8 @@ export default class BattleScene extends SceneBase {
   public inputController: InputsController;
   public uiInputs: UiInputs;
 
-  public sessionPlayTime: integer = null;
-  public lastSavePlayTime: integer = null;
+  public sessionPlayTime: integer | null = null;
+  public lastSavePlayTime: integer | null = null;
   public masterVolume: number = 0.5;
   public bgmVolume: number = 1;
   public seVolume: number = 1;
@@ -192,8 +192,8 @@ export default class BattleScene extends SceneBase {
   private phaseQueuePrependSpliceIndex: integer;
   private nextCommandPhaseQueue: Phase[];
 
-  private currentPhase: Phase;
-  private standbyPhase: Phase;
+  private currentPhase: Phase | null;
+  private standbyPhase: Phase | null;
   public field: Phaser.GameObjects.Container;
   public fieldUI: Phaser.GameObjects.Container;
   public charSprite: CharSprite;
@@ -213,7 +213,7 @@ export default class BattleScene extends SceneBase {
   public score: integer;
   public lockModifierTiers: boolean;
   public trainer: Phaser.GameObjects.Sprite;
-  public lastEnemyTrainer: Trainer;
+  public lastEnemyTrainer: Trainer | null;
   public currentBattle: Battle;
   public pokeballCounts: PokeballCounts;
   public money: integer;
@@ -251,7 +251,7 @@ export default class BattleScene extends SceneBase {
   public spritePipeline: SpritePipeline;
 
   private bgm: AnySound;
-  private bgmResumeTimer: Phaser.Time.TimerEvent;
+  private bgmResumeTimer: Phaser.Time.TimerEvent | null;
   private bgmCache: Set<string> = new Set();
   private playTimeTimer: Phaser.Time.TimerEvent;
 
@@ -700,7 +700,11 @@ export default class BattleScene extends SceneBase {
 
   hasExpSprite(key: string): boolean {
     const keyMatch = /^pkmn__?(back__)?(shiny__)?(female__)?(\d+)(\-.*?)?(?:_[1-3])?$/g.exec(key);
-    let k = keyMatch[4];
+    if (!keyMatch) {
+      return false;
+    }
+
+    let k = keyMatch[4]!;
     if (keyMatch[2]) {
       k += "s";
     }
@@ -723,7 +727,7 @@ export default class BattleScene extends SceneBase {
     return this.party;
   }
 
-  getPlayerPokemon(): PlayerPokemon {
+  getPlayerPokemon(): PlayerPokemon | undefined {
     return this.getPlayerField().find(p => p.isActive());
   }
 
@@ -740,7 +744,7 @@ export default class BattleScene extends SceneBase {
     return this.currentBattle?.enemyParty || [];
   }
 
-  getEnemyPokemon(): EnemyPokemon {
+  getEnemyPokemon(): EnemyPokemon | undefined {
     return this.getEnemyField().find(p => p.isActive());
   }
 
@@ -782,12 +786,12 @@ export default class BattleScene extends SceneBase {
     return activeOnly ? this.infoToggles.filter(t => t?.isActive()) : this.infoToggles;
   }
 
-  getPokemonById(pokemonId: integer): Pokemon {
+  getPokemonById(pokemonId: integer): Pokemon | null {
     const findInParty = (party: Pokemon[]) => party.find(p => p.id === pokemonId);
-    return findInParty(this.getParty()) || findInParty(this.getEnemyParty());
+    return (findInParty(this.getParty()) || findInParty(this.getEnemyParty())) ?? null;
   }
 
-  addPlayerPokemon(species: PokemonSpecies, level: integer, abilityIndex: integer, formIndex: integer, gender?: Gender, shiny?: boolean, variant?: Variant, ivs?: integer[], nature?: Nature, dataSource?: Pokemon | PokemonData, postProcess?: (playerPokemon: PlayerPokemon) => void): PlayerPokemon {
+  addPlayerPokemon(species: PokemonSpecies, level: integer, abilityIndex?: integer, formIndex?: integer, gender?: Gender, shiny?: boolean, variant?: Variant, ivs?: integer[], nature?: Nature, dataSource?: Pokemon | PokemonData, postProcess?: (playerPokemon: PlayerPokemon) => void): PlayerPokemon {
     const pokemon = new PlayerPokemon(this, species, level, abilityIndex, formIndex, gender, shiny, variant, ivs, nature, dataSource);
     if (postProcess) {
       postProcess(pokemon);
@@ -957,7 +961,8 @@ export default class BattleScene extends SceneBase {
       p.destroy();
     }
 
-    this.currentBattle = null;
+    //@ts-ignore  - allowing `null` for currentBattle causes a lot of trouble
+    this.currentBattle = null; // TODO: resolve ts-ignore
 
     this.biomeWaveText.setText(startingWave.toString());
     this.biomeWaveText.setVisible(false);
@@ -1021,14 +1026,14 @@ export default class BattleScene extends SceneBase {
     }
   }
 
-  newBattle(waveIndex?: integer, battleType?: BattleType, trainerData?: TrainerData, double?: boolean): Battle {
+  newBattle(waveIndex?: integer, battleType?: BattleType, trainerData?: TrainerData, double?: boolean): Battle | null {
     const _startingWave = Overrides.STARTING_WAVE_OVERRIDE || startingWave;
     const newWaveIndex = waveIndex || ((this.currentBattle?.waveIndex || (_startingWave - 1)) + 1);
-    let newDouble: boolean;
+    let newDouble: boolean | undefined;
     let newBattleType: BattleType;
-    let newTrainer: Trainer;
+    let newTrainer: Trainer | undefined;
 
-    let battleConfig: FixedBattleConfig = null;
+    let battleConfig: FixedBattleConfig | null = null;
 
     this.resetSeed(newWaveIndex);
 
@@ -1038,7 +1043,7 @@ export default class BattleScene extends SceneBase {
       battleConfig = this.gameMode.getFixedBattle(newWaveIndex);
       newDouble = battleConfig.double;
       newBattleType = battleConfig.battleType;
-      this.executeWithSeedOffset(() => newTrainer = battleConfig.getTrainer(this), (battleConfig.seedOffsetWaveIndex || newWaveIndex) << 8);
+      this.executeWithSeedOffset(() => newTrainer = battleConfig?.getTrainer(this), (battleConfig.seedOffsetWaveIndex || newWaveIndex) << 8);
       if (newTrainer) {
         this.field.add(newTrainer);
       }
@@ -1078,7 +1083,7 @@ export default class BattleScene extends SceneBase {
         playerField.forEach(p => applyAbAttrs(DoubleBattleChanceAbAttr, p, null, doubleChance));
         newDouble = !Utils.randSeedInt(doubleChance.value);
       } else if (newBattleType === BattleType.TRAINER) {
-        newDouble = newTrainer.variant === TrainerVariant.DOUBLE;
+        newDouble = newTrainer?.variant === TrainerVariant.DOUBLE;
       }
     } else if (!battleConfig) {
       newDouble = !!double;
@@ -1309,7 +1314,7 @@ export default class BattleScene extends SceneBase {
       return 5;
     }
 
-    let isBoss: boolean;
+    let isBoss: boolean | undefined;
     if (forceBoss || (species && (species.subLegendary || species.legendary || species.mythical))) {
       isBoss = true;
     } else {
@@ -1608,7 +1613,7 @@ export default class BattleScene extends SceneBase {
 
   randomSpecies(waveIndex: integer, level: integer, fromArenaPool?: boolean, speciesFilter?: PokemonSpeciesFilter, filterAllEvolutions?: boolean): PokemonSpecies {
     if (fromArenaPool) {
-      return this.arena.randomSpecies(waveIndex, level,null , getPartyLuckValue(this.party));
+      return this.arena.randomSpecies(waveIndex, level, undefined , getPartyLuckValue(this.party));
     }
     const filteredSpecies = speciesFilter ? [...new Set(allSpecies.filter(s => s.isCatchable()).filter(speciesFilter).map(s => {
       if (!filterAllEvolutions) {
@@ -1966,11 +1971,11 @@ export default class BattleScene extends SceneBase {
   }
 
   /* Phase Functions */
-  getCurrentPhase(): Phase {
+  getCurrentPhase(): Phase | null {
     return this.currentPhase;
   }
 
-  getStandbyPhase(): Phase {
+  getStandbyPhase(): Phase | null {
     return this.standbyPhase;
   }
 
@@ -2048,7 +2053,10 @@ export default class BattleScene extends SceneBase {
     }
     if (this.phaseQueuePrepend.length) {
       while (this.phaseQueuePrepend.length) {
-        this.phaseQueue.unshift(this.phaseQueuePrepend.pop());
+        const poppedPhase = this.phaseQueuePrepend.pop();
+        if (poppedPhase) {
+          this.phaseQueue.unshift(poppedPhase);
+        }
       }
     }
     if (!this.phaseQueue.length) {
@@ -2056,23 +2064,26 @@ export default class BattleScene extends SceneBase {
       // Clear the conditionalQueue if there are no phases left in the phaseQueue
       this.conditionalQueue = [];
     }
-    this.currentPhase = this.phaseQueue.shift();
+
+    this.currentPhase = this.phaseQueue.shift() ?? null;
 
     // Check if there are any conditional phases queued
     if (this.conditionalQueue?.length) {
       // Retrieve the first conditional phase from the queue
       const conditionalPhase = this.conditionalQueue.shift();
       // Evaluate the condition associated with the phase
-      if (conditionalPhase[0]()) {
+      if (conditionalPhase?.[0]()) {
         // If the condition is met, add the phase to the phase queue
         this.pushPhase(conditionalPhase[1]);
-      } else {
+      } else if (conditionalPhase) {
         // If the condition is not met, re-add the phase back to the front of the conditional queue
         this.conditionalQueue.unshift(conditionalPhase);
+      } else {
+        console.warn("condition phase is undefined/null!", conditionalPhase);
       }
     }
 
-    this.currentPhase.start();
+    this.currentPhase?.start();
   }
 
   overridePhase(phase: Phase): boolean {
@@ -2087,7 +2098,7 @@ export default class BattleScene extends SceneBase {
     return true;
   }
 
-  findPhase(phaseFilter: (phase: Phase) => boolean): Phase {
+  findPhase(phaseFilter: (phase: Phase) => boolean): Phase | undefined {
     return this.phaseQueue.find(phaseFilter);
   }
 
@@ -2146,7 +2157,7 @@ export default class BattleScene extends SceneBase {
    * @param promptDelay optional param for MessagePhase constructor
    * @param defer boolean for which queue to add it to, false -> add to PhaseQueuePrepend, true -> nextCommandPhaseQueue
    */
-  queueMessage(message: string, callbackDelay?: integer, prompt?: boolean, promptDelay?: integer, defer?: boolean) {
+  queueMessage(message: string, callbackDelay?: integer | null, prompt?: boolean | null, promptDelay?: integer | null, defer?: boolean | null) {
     const phase = new MessagePhase(this, message, callbackDelay, prompt, promptDelay);
     if (!defer) {
       // adds to the end of PhaseQueuePrepend
@@ -2182,7 +2193,10 @@ export default class BattleScene extends SceneBase {
     return Math.floor(moneyValue / 10) * 10;
   }
 
-  addModifier(modifier: Modifier, ignoreUpdate?: boolean, playSound?: boolean, virtual?: boolean, instant?: boolean): Promise<boolean> {
+  addModifier(modifier: Modifier | null, ignoreUpdate?: boolean, playSound?: boolean, virtual?: boolean, instant?: boolean): Promise<boolean> {
+    if (!modifier) {
+      return Promise.resolve(false);
+    }
     return new Promise(resolve => {
       let success = false;
       const soundName = modifier.type.soundName;
@@ -2202,7 +2216,7 @@ export default class BattleScene extends SceneBase {
           }
         } else if (!virtual) {
           const defaultModifierType = getDefaultModifierTypeForTier(modifier.type.tier);
-          this.queueMessage(`The stack for this item is full.\n You will receive ${defaultModifierType.name} instead.`, null, true);
+          this.queueMessage(`The stack for this item is full.\n You will receive ${defaultModifierType.name} instead.`, undefined, true);
           return this.addModifier(defaultModifierType.newModifier(), ignoreUpdate, playSound, false, instant).then(success => resolve(success));
         }
 
@@ -2302,7 +2316,7 @@ export default class BattleScene extends SceneBase {
     return new Promise(resolve => {
       const source = itemModifier.pokemonId ? itemModifier.getPokemon(target.scene) : null;
       const cancelled = new Utils.BooleanHolder(false);
-      Utils.executeIf(source && source.isPlayer() !== target.isPlayer(), () => applyAbAttrs(BlockItemTheftAbAttr, source, cancelled)).then(() => {
+      Utils.executeIf(!!source && source.isPlayer() !== target.isPlayer(), () => applyAbAttrs(BlockItemTheftAbAttr, source! /* checked in condition*/, cancelled)).then(() => {
         if (cancelled.value) {
           return resolve(false);
         }
@@ -2383,7 +2397,7 @@ export default class BattleScene extends SceneBase {
       }
 
       party.forEach((enemyPokemon: EnemyPokemon, i: integer) => {
-        const isBoss = enemyPokemon.isBoss() || (this.currentBattle.battleType === BattleType.TRAINER && this.currentBattle.trainer.config.isBoss);
+        const isBoss = enemyPokemon.isBoss() || (this.currentBattle.battleType === BattleType.TRAINER && this.currentBattle.trainer?.config.isBoss);
         let upgradeChance = 32;
         if (isBoss) {
           upgradeChance /= 2;
@@ -2391,9 +2405,9 @@ export default class BattleScene extends SceneBase {
         if (isFinalBoss) {
           upgradeChance /= 8;
         }
-        const modifierChance = this.gameMode.getEnemyModifierChance(isBoss);
+        const modifierChance = this.gameMode.getEnemyModifierChance(isBoss!); // TODO: is this bang correct?
         let pokemonModifierChance = modifierChance;
-        if (this.currentBattle.battleType === BattleType.TRAINER)
+        if (this.currentBattle.battleType === BattleType.TRAINER && this.currentBattle.trainer)
           pokemonModifierChance = Math.ceil(pokemonModifierChance * this.currentBattle.trainer.getPartyMemberModifierChanceMultiplier(i)); // eslint-disable-line
         let count = 0;
         for (let c = 0; c < chances; c++) {
@@ -2512,7 +2526,7 @@ export default class BattleScene extends SceneBase {
     return (player ? this.modifiers : this.enemyModifiers).filter(m => (modifierFilter as ModifierPredicate)(m));
   }
 
-  findModifier(modifierFilter: ModifierPredicate, player: boolean = true): PersistentModifier {
+  findModifier(modifierFilter: ModifierPredicate, player: boolean = true): PersistentModifier | undefined {
     return (player ? this.modifiers : this.enemyModifiers).find(m => (modifierFilter as ModifierPredicate)(m));
   }
 
@@ -2548,7 +2562,7 @@ export default class BattleScene extends SceneBase {
     return appliedModifiers;
   }
 
-  applyModifier(modifierType: Constructor<Modifier>, player: boolean = true, ...args: any[]): PersistentModifier {
+  applyModifier(modifierType: Constructor<Modifier>, player: boolean = true, ...args: any[]): PersistentModifier | null {
     const modifiers = (player ? this.modifiers : this.enemyModifiers).filter(m => m instanceof modifierType && m.shouldApply(args));
     for (const modifier of modifiers) {
       if (modifier.apply(args)) {
@@ -2635,7 +2649,7 @@ export default class BattleScene extends SceneBase {
   initFinalBossPhaseTwo(pokemon: Pokemon): void {
     if (pokemon instanceof EnemyPokemon && pokemon.isBoss() && !pokemon.formIndex && pokemon.bossSegmentIndex < 1) {
       this.fadeOutBgm(Utils.fixedInt(2000), false);
-      this.ui.showDialogue(battleSpecDialogue[BattleSpec.FINAL_BOSS].firstStageWin, pokemon.species.name, null, () => {
+      this.ui.showDialogue(battleSpecDialogue[BattleSpec.FINAL_BOSS].firstStageWin, pokemon.species.name, undefined, () => {
         this.addEnemyModifier(getModifierType(modifierTypes.MINI_BLACK_HOLE).newModifier(pokemon) as PersistentModifier, false, true);
         pokemon.generateAndPopulateMoveset(1);
         this.setFieldScale(0.75);
diff --git a/src/battle.ts b/src/battle.ts
index 8a1309938f7..0b3b256f3df 100644
--- a/src/battle.ts
+++ b/src/battle.ts
@@ -39,7 +39,7 @@ export interface TurnCommand {
 }
 
 interface TurnCommands {
-    [key: integer]: TurnCommand
+    [key: integer]: TurnCommand | null
 }
 
 export default class Battle {
@@ -47,8 +47,8 @@ export default class Battle {
   public waveIndex: integer;
   public battleType: BattleType;
   public battleSpec: BattleSpec;
-  public trainer: Trainer;
-  public enemyLevels: integer[];
+  public trainer: Trainer | null;
+  public enemyLevels: integer[] | undefined;
   public enemyParty: EnemyPokemon[];
   public seenEnemyPartyMemberIds: Set<integer>;
   public double: boolean;
@@ -62,26 +62,26 @@ export default class Battle {
   public escapeAttempts: integer;
   public lastMove: Moves;
   public battleSeed: string;
-  private battleSeedState: string;
+  private battleSeedState: string | null;
   public moneyScattered: number;
-  public lastUsedPokeball: PokeballType;
+  public lastUsedPokeball: PokeballType | null;
   public playerFaints: number; // The amount of times pokemon on the players side have fainted
   public enemyFaints: number; // The amount of times pokemon on the enemies side have fainted
 
   private rngCounter: integer = 0;
 
-  constructor(gameMode: GameMode, waveIndex: integer, battleType: BattleType, trainer: Trainer, double: boolean) {
+  constructor(gameMode: GameMode, waveIndex: integer, battleType: BattleType, trainer?: Trainer, double?: boolean) {
     this.gameMode = gameMode;
     this.waveIndex = waveIndex;
     this.battleType = battleType;
-    this.trainer = trainer;
+    this.trainer = trainer!; //TODO: is this bang correct?
     this.initBattleSpec();
     this.enemyLevels = battleType !== BattleType.TRAINER
       ? new Array(double ? 2 : 1).fill(null).map(() => this.getLevelForWave())
-      : trainer.getPartyLevels(this.waveIndex);
+      : trainer?.getPartyLevels(this.waveIndex);
     this.enemyParty = [];
     this.seenEnemyPartyMemberIds = new Set<integer>();
-    this.double = double;
+    this.double = double!; //TODO: is this bang correct?
     this.enemySwitchCounter = 0;
     this.turn = 0;
     this.playerParticipantIds = new Set<integer>();
@@ -159,6 +159,7 @@ export default class Battle {
   addPostBattleLoot(enemyPokemon: EnemyPokemon): void {
     this.postBattleLoot.push(...enemyPokemon.scene.findModifiers(m => m instanceof PokemonHeldItemModifier && m.pokemonId === enemyPokemon.id && m.isTransferrable, false).map(i => {
       const ret = i as PokemonHeldItemModifier;
+      //@ts-ignore - this is awful to fix/change
       ret.pokemonId = null;
       return ret;
     }));
@@ -177,7 +178,7 @@ export default class Battle {
     const userLocale = navigator.language || "en-US";
     const formattedMoneyAmount = moneyAmount.value.toLocaleString(userLocale);
     const message = i18next.t("battle:moneyPickedUp", { moneyAmount: formattedMoneyAmount });
-    scene.queueMessage(message, null, true);
+    scene.queueMessage(message, undefined, true);
 
     scene.currentBattle.moneyScattered = 0;
   }
@@ -200,16 +201,16 @@ export default class Battle {
     scene.updateScoreText();
   }
 
-  getBgmOverride(scene: BattleScene): string {
+  getBgmOverride(scene: BattleScene): string | null {
     const battlers = this.enemyParty.slice(0, this.getBattlerCount());
     if (this.battleType === BattleType.TRAINER) {
-      if (!this.started && this.trainer.config.encounterBgm && this.trainer.getEncounterMessages()?.length) {
-        return `encounter_${this.trainer.getEncounterBgm()}`;
+      if (!this.started && this.trainer?.config.encounterBgm && this.trainer?.getEncounterMessages()?.length) {
+        return `encounter_${this.trainer?.getEncounterBgm()}`;
       }
       if (scene.musicPreference === 0) {
-        return this.trainer.getBattleBgm();
+        return this.trainer?.getBattleBgm()!; // TODO: is this bang correct?
       } else {
-        return this.trainer.getMixedBattleBgm();
+        return this.trainer?.getMixedBattleBgm()!; // TODO: is this bang correct?
       }
     } else if (this.gameMode.isClassic && this.waveIndex > 195 && this.battleSpec !== BattleSpec.FINAL_BOSS) {
       return "end_summit";
@@ -382,7 +383,7 @@ export default class Battle {
 
 export class FixedBattle extends Battle {
   constructor(scene: BattleScene, waveIndex: integer, config: FixedBattleConfig) {
-    super(scene.gameMode, waveIndex, config.battleType, config.battleType === BattleType.TRAINER ? config.getTrainer(scene) : null, config.double);
+    super(scene.gameMode, waveIndex, config.battleType, config.battleType === BattleType.TRAINER ? config.getTrainer(scene) : undefined, config.double);
     if (config.getEnemyParty) {
       this.enemyParty = config.getEnemyParty(scene);
     }
diff --git a/src/configs/inputs/configHandler.ts b/src/configs/inputs/configHandler.ts
index a67c45fd413..45fb033e9fa 100644
--- a/src/configs/inputs/configHandler.ts
+++ b/src/configs/inputs/configHandler.ts
@@ -20,7 +20,7 @@ export function getKeyWithKeycode(config, keycode) {
  */
 export function getSettingNameWithKeycode(config, keycode) {
   const key = getKeyWithKeycode(config, keycode);
-  return config.custom[key];
+  return key ? config.custom[key] : null;
 }
 
 /**
@@ -32,7 +32,7 @@ export function getSettingNameWithKeycode(config, keycode) {
  */
 export function getIconWithKeycode(config, keycode) {
   const key = getKeyWithKeycode(config, keycode);
-  return config.icons[key];
+  return key ? config.icons[key] : null;
 }
 
 /**
@@ -122,15 +122,21 @@ export function assign(config, settingNameTarget, keycode): boolean {
   // if it was already bound, we delete the bind
   if (previousSettingName) {
     const previousKey = getKeyWithSettingName(config, previousSettingName);
-    config.custom[previousKey] = -1;
+    if (previousKey) {
+      config.custom[previousKey] = -1;
+    }
   }
   // then, we need to delete the current key for this settingName
   const currentKey = getKeyWithSettingName(config, settingNameTarget);
-  config.custom[currentKey] = -1;
+  if (currentKey) {
+    config.custom[currentKey] = -1;
+  }
 
   // then, the new key is assigned to the new settingName
   const newKey = getKeyWithKeycode(config, keycode);
-  config.custom[newKey] = settingNameTarget;
+  if (newKey) {
+    config.custom[newKey] = settingNameTarget;
+  }
   return true;
 }
 
@@ -145,8 +151,12 @@ export function swap(config, settingNameTarget, keycode) {
   const new_key = getKeyWithKeycode(config, keycode);
   const new_settingName = getSettingNameWithKey(config, new_key);
 
-  config.custom[prev_key] = new_settingName;
-  config.custom[new_key] = prev_settingName;
+  if (prev_key) {
+    config.custom[prev_key] = new_settingName;
+  }
+  if (new_key) {
+    config.custom[new_key] = prev_settingName;
+  }
   return true;
 }
 
@@ -161,7 +171,9 @@ export function deleteBind(config, settingName) {
   if (config.blacklist.includes(key)) {
     return false;
   }
-  config.custom[key] = -1;
+  if (key) {
+    config.custom[key] = -1;
+  }
   return true;
 }
 
diff --git a/src/data/ability.ts b/src/data/ability.ts
index b483998612e..f4701d3a4e1 100644
--- a/src/data/ability.ts
+++ b/src/data/ability.ts
@@ -120,7 +120,7 @@ export class Ability implements Localizable {
 type AbAttrApplyFunc<TAttr extends AbAttr> = (attr: TAttr, passive: boolean) => boolean | Promise<boolean>;
 type AbAttrCondition = (pokemon: Pokemon) => boolean;
 
-type PokemonAttackCondition = (user: Pokemon, target: Pokemon, move: Move) => boolean;
+type PokemonAttackCondition = (user: Pokemon | null, target: Pokemon | null, move: Move) => boolean;
 type PokemonDefendCondition = (target: Pokemon, user: Pokemon, move: Move) => boolean;
 type PokemonStatChangeCondition = (target: Pokemon, statsChanged: BattleStat[], levels: integer) => boolean;
 
@@ -132,11 +132,11 @@ export abstract class AbAttr {
     this.showAbility = showAbility;
   }
 
-  apply(pokemon: Pokemon, passive: boolean, cancelled: Utils.BooleanHolder, args: any[]): boolean | Promise<boolean> {
+  apply(pokemon: Pokemon, passive: boolean, cancelled: Utils.BooleanHolder | null, args: any[]): boolean | Promise<boolean> {
     return false;
   }
 
-  getTriggerMessage(pokemon: Pokemon, abilityName: string, ...args: any[]): string {
+  getTriggerMessage(_pokemon: Pokemon, _abilityName: string, ..._args: any[]): string | null {
     return null;
   }
 
@@ -226,7 +226,7 @@ export class PostBattleInitStatChangeAbAttr extends PostBattleInitAbAttr {
     }
 
     for (const statChangePhase of statChangePhases) {
-      if (!this.selfTarget && !statChangePhase.getPokemon().summonData) {
+      if (!this.selfTarget && !statChangePhase.getPokemon()?.summonData) {
         pokemon.scene.pushPhase(statChangePhase);
       } else { // TODO: This causes the ability bar to be shown at the wrong time
         pokemon.scene.unshiftPhase(statChangePhase);
@@ -240,7 +240,7 @@ export class PostBattleInitStatChangeAbAttr extends PostBattleInitAbAttr {
 type PreDefendAbAttrCondition = (pokemon: Pokemon, attacker: Pokemon, move: Move) => boolean;
 
 export class PreDefendAbAttr extends AbAttr {
-  applyPreDefend(pokemon: Pokemon, passive: boolean, attacker: Pokemon, move: Move, cancelled: Utils.BooleanHolder, args: any[]): boolean | Promise<boolean> {
+  applyPreDefend(pokemon: Pokemon, passive: boolean, attacker: Pokemon, move: Move | null, cancelled: Utils.BooleanHolder | null, args: any[]): boolean | Promise<boolean> {
     return false;
   }
 }
@@ -352,14 +352,14 @@ export class PreDefendMoveDamageToOneAbAttr extends ReceivedMoveDamageMultiplier
  * @see {@linkcode getCondition}
  */
 export class TypeImmunityAbAttr extends PreDefendAbAttr {
-  private immuneType: Type;
-  private condition: AbAttrCondition;
+  private immuneType: Type | null;
+  private condition: AbAttrCondition | null;
 
-  constructor(immuneType: Type, condition?: AbAttrCondition) {
+  constructor(immuneType: Type | null, condition?: AbAttrCondition) {
     super();
 
     this.immuneType = immuneType;
-    this.condition = condition;
+    this.condition = condition!; // TODO: is this bang correct?
   }
 
   /**
@@ -386,7 +386,7 @@ export class TypeImmunityAbAttr extends PreDefendAbAttr {
     return false;
   }
 
-  getCondition(): AbAttrCondition {
+  override getCondition(): AbAttrCondition | null {
     return this.condition;
   }
 }
@@ -491,7 +491,7 @@ export class NonSuperEffectiveImmunityAbAttr extends TypeImmunityAbAttr {
 }
 
 export class PostDefendAbAttr extends AbAttr {
-  applyPostDefend(pokemon: Pokemon, passive: boolean, attacker: Pokemon, move: Move, hitResult: HitResult, args: any[]): boolean | Promise<boolean> {
+  applyPostDefend(pokemon: Pokemon, passive: boolean, attacker: Pokemon, move: Move, hitResult: HitResult | null, args: any[]): boolean | Promise<boolean> {
     return false;
   }
 }
@@ -881,7 +881,7 @@ export class EffectSporeAbAttr extends PostDefendContactApplyStatusEffectAbAttr
 export class PostDefendContactApplyTagChanceAbAttr extends PostDefendAbAttr {
   private chance: integer;
   private tagType: BattlerTagType;
-  private turnCount: integer;
+  private turnCount: integer | undefined;
 
   constructor(chance: integer, tagType: BattlerTagType, turnCount?: integer) {
     super();
@@ -918,7 +918,7 @@ export class PostDefendCritStatChangeAbAttr extends PostDefendAbAttr {
   }
 
   getCondition(): AbAttrCondition {
-    return (pokemon: Pokemon) => pokemon.turnData.attacksReceived.length && pokemon.turnData.attacksReceived[pokemon.turnData.attacksReceived.length - 1].critical;
+    return (pokemon: Pokemon) => pokemon.turnData.attacksReceived.length !== 0 && pokemon.turnData.attacksReceived[pokemon.turnData.attacksReceived.length - 1].critical;
   }
 }
 
@@ -1109,7 +1109,7 @@ export class PostStatChangeStatChangeAbAttr extends PostStatChangeAbAttr {
 }
 
 export class PreAttackAbAttr extends AbAttr {
-  applyPreAttack(pokemon: Pokemon, passive: boolean, defender: Pokemon, move: Move, args: any[]): boolean | Promise<boolean> {
+  applyPreAttack(pokemon: Pokemon, passive: boolean, defender: Pokemon | null, move: Move, args: any[]): boolean | Promise<boolean> {
     return false;
   }
 }
@@ -1122,7 +1122,7 @@ export class PreAttackAbAttr extends AbAttr {
 export class MoveEffectChanceMultiplierAbAttr extends AbAttr {
   private chanceMultiplier: number;
 
-  constructor(chanceMultiplier?: number) {
+  constructor(chanceMultiplier: number) {
     super(true);
     this.chanceMultiplier = chanceMultiplier;
   }
@@ -1503,7 +1503,7 @@ export class FieldMovePowerBoostAbAttr extends AbAttr {
     this.powerMultiplier = powerMultiplier;
   }
 
-  applyPreAttack(pokemon: Pokemon, passive: boolean, defender: Pokemon, move: Move, args: any[]): boolean {
+  applyPreAttack(pokemon: Pokemon | null, passive: boolean | null, defender: Pokemon | null, move: Move, args: any[]): boolean {
     if (this.condition(pokemon, defender, move)) {
       (args[0] as Utils.NumberHolder).value *= this.powerMultiplier;
 
@@ -1557,14 +1557,14 @@ export class AllyMoveCategoryPowerBoostAbAttr extends FieldMovePowerBoostAbAttr
 export class BattleStatMultiplierAbAttr extends AbAttr {
   private battleStat: BattleStat;
   private multiplier: number;
-  private condition: PokemonAttackCondition;
+  private condition: PokemonAttackCondition | null;
 
   constructor(battleStat: BattleStat, multiplier: number, condition?: PokemonAttackCondition) {
     super(false);
 
     this.battleStat = battleStat;
     this.multiplier = multiplier;
-    this.condition = condition;
+    this.condition = condition!; // TODO: is this bang correct?
   }
 
   applyBattleStat(pokemon: Pokemon, passive: boolean, battleStat: BattleStat, statValue: Utils.NumberHolder, args: any[]): boolean | Promise<boolean> {
@@ -1593,7 +1593,7 @@ export class PostAttackAbAttr extends AbAttr {
    * applying the effect of any inherited class. This can be changed by providing a different {@link attackCondition} to the constructor. See {@link ConfusionOnStatusEffectAbAttr}
    * for an example of an effect that does not require a damaging move.
    */
-  applyPostAttack(pokemon: Pokemon, passive: boolean, defender: Pokemon, move: Move, hitResult: HitResult, args: any[]): boolean | Promise<boolean> {
+  applyPostAttack(pokemon: Pokemon, passive: boolean, defender: Pokemon, move: Move, hitResult: HitResult | null, args: any[]): boolean | Promise<boolean> {
     // When attackRequired is true, we require the move to be an attack move and to deal damage before checking secondary requirements.
     // If attackRequired is false, we always defer to the secondary requirements.
     if (this.attackCondition(pokemon, defender, move)) {
@@ -1606,18 +1606,18 @@ export class PostAttackAbAttr extends AbAttr {
   /**
    * This method is only called after {@link applyPostAttack} has already been applied. Use this for handling checks specific to the ability in question.
    */
-  applyPostAttackAfterMoveTypeCheck(pokemon: Pokemon, passive: boolean, defender: Pokemon, move: Move, hitResult: HitResult, args: any[]): boolean | Promise<boolean> {
+  applyPostAttackAfterMoveTypeCheck(pokemon: Pokemon, passive: boolean, defender: Pokemon, move: Move, hitResult: HitResult | null, args: any[]): boolean | Promise<boolean> {
     return false;
   }
 }
 
 export class PostAttackStealHeldItemAbAttr extends PostAttackAbAttr {
-  private stealCondition: PokemonAttackCondition;
+  private stealCondition: PokemonAttackCondition | null;
 
   constructor(stealCondition?: PokemonAttackCondition) {
     super();
 
-    this.stealCondition = stealCondition;
+    this.stealCondition = stealCondition!; // TODO: is this bang correct?
   }
 
   applyPostAttackAfterMoveTypeCheck(pokemon: Pokemon, passive: boolean, defender: Pokemon, move: Move, hitResult: HitResult, args: any[]): Promise<boolean> {
@@ -1701,12 +1701,12 @@ export class PostAttackApplyBattlerTagAbAttr extends PostAttackAbAttr {
 }
 
 export class PostDefendStealHeldItemAbAttr extends PostDefendAbAttr {
-  private condition: PokemonDefendCondition;
+  private condition: PokemonDefendCondition | null;
 
   constructor(condition?: PokemonDefendCondition) {
     super();
 
-    this.condition = condition;
+    this.condition = condition!; // TODO: is this bang correct?
   }
 
   applyPostDefend(pokemon: Pokemon, passive: boolean, attacker: Pokemon, move: Move, hitResult: HitResult, args: any[]): Promise<boolean> {
@@ -2197,17 +2197,17 @@ export class PostSummonCopyAbilityAbAttr extends PostSummonAbAttr {
     }
 
     if (
-      target.getAbility().hasAttr(UncopiableAbilityAbAttr) &&
+      target!.getAbility().hasAttr(UncopiableAbilityAbAttr) &&
       // Wonder Guard is normally uncopiable so has the attribute, but Trace specifically can copy it
-      !(pokemon.hasAbility(Abilities.TRACE) && target.getAbility().id === Abilities.WONDER_GUARD)
+      !(pokemon.hasAbility(Abilities.TRACE) && target!.getAbility().id === Abilities.WONDER_GUARD)
     ) {
       return false;
     }
 
-    this.target = target;
-    this.targetAbilityName = allAbilities[target.getAbility().id].name;
-    pokemon.summonData.ability = target.getAbility().id;
-    setAbilityRevealed(target);
+    this.target = target!;
+    this.targetAbilityName = allAbilities[target!.getAbility().id].name;
+    pokemon.summonData.ability = target!.getAbility().id;
+    setAbilityRevealed(target!);
     pokemon.updateInfo();
 
     return true;
@@ -2254,7 +2254,7 @@ export class PostSummonUserFieldRemoveStatusEffectAbAttr extends PostSummonAbAtt
     }
 
     for (const pokemon of allowedParty) {
-      if (this.statusEffect.includes(pokemon.status?.effect)) {
+      if (pokemon.status && this.statusEffect.includes(pokemon.status.effect)) {
         pokemon.scene.queueMessage(getStatusEffectHealText(pokemon.status.effect, getPokemonNameWithAffix(pokemon)));
         pokemon.resetStatus(false);
         pokemon.updateInfo();
@@ -2310,6 +2310,7 @@ export class PostSummonTransformAbAttr extends PostSummonAbAttr {
       target = targets[0];
     }
 
+    target = target!; // compiler doesn't know its guranteed to be defined
     pokemon.summonData.speciesForm = target.getSpeciesForm();
     pokemon.summonData.fusionSpeciesForm = target.getFusionSpeciesForm();
     pokemon.summonData.ability = target.getAbility().id;
@@ -2317,7 +2318,7 @@ export class PostSummonTransformAbAttr extends PostSummonAbAttr {
     pokemon.summonData.fusionGender = target.getFusionGender();
     pokemon.summonData.stats = [ pokemon.stats[Stat.HP] ].concat(target.stats.slice(1));
     pokemon.summonData.battleStats = target.summonData.battleStats.slice(0);
-    pokemon.summonData.moveset = target.getMoveset().map(m => new PokemonMove(m.moveId, m.ppUsed, m.ppUp));
+    pokemon.summonData.moveset = target.getMoveset().map(m => new PokemonMove(m!.moveId, m!.ppUsed, m!.ppUp)); // TODO: are those bangs correct?
     pokemon.summonData.types = target.getTypes();
 
     pokemon.scene.playSound("PRSFX- Transform");
@@ -2364,7 +2365,7 @@ export class PreSwitchOutClearWeatherAbAttr extends PreSwitchOutAbAttr {
    * @returns {boolean} Returns true if the weather clears, otherwise false.
    */
   applyPreSwitchOut(pokemon: Pokemon, passive: boolean, args: any[]): boolean | Promise<boolean> {
-    const weatherType = pokemon.scene.arena.weather.weatherType;
+    const weatherType = pokemon.scene.arena.weather?.weatherType;
     let turnOffWeather = false;
 
     // Clear weather only if user's ability matches the weather and no other pokemon has the ability.
@@ -2445,18 +2446,18 @@ export class PreSwitchOutFormChangeAbAttr extends PreSwitchOutAbAttr {
 }
 
 export class PreStatChangeAbAttr extends AbAttr {
-  applyPreStatChange(pokemon: Pokemon, passive: boolean, stat: BattleStat, cancelled: Utils.BooleanHolder, args: any[]): boolean | Promise<boolean> {
+  applyPreStatChange(pokemon: Pokemon | null, passive: boolean, stat: BattleStat, cancelled: Utils.BooleanHolder, args: any[]): boolean | Promise<boolean> {
     return false;
   }
 }
 
 export class ProtectStatAbAttr extends PreStatChangeAbAttr {
-  private protectedStat: BattleStat;
+  private protectedStat: BattleStat | null;
 
   constructor(protectedStat?: BattleStat) {
     super();
 
-    this.protectedStat = protectedStat;
+    this.protectedStat = protectedStat!; // TODO: is this bang correct?
   }
 
   applyPreStatChange(pokemon: Pokemon, passive: boolean, stat: BattleStat, cancelled: Utils.BooleanHolder, args: any[]): boolean {
@@ -2472,7 +2473,7 @@ export class ProtectStatAbAttr extends PreStatChangeAbAttr {
     return i18next.t("abilityTriggers:protectStat", {
       pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
       abilityName,
-      statName: this.protectedStat !== undefined ? getBattleStatName(this.protectedStat) : i18next.t("battle:stats")
+      statName: this.protectedStat ? getBattleStatName(this.protectedStat) : i18next.t("battle:stats")
     });
   }
 }
@@ -2512,7 +2513,7 @@ export class ConfusionOnStatusEffectAbAttr extends PostAttackAbAttr {
 }
 
 export class PreSetStatusAbAttr extends AbAttr {
-  applyPreSetStatus(pokemon: Pokemon, passive: boolean, effect: StatusEffect, cancelled: Utils.BooleanHolder, args: any[]): boolean | Promise<boolean> {
+  applyPreSetStatus(pokemon: Pokemon, passive: boolean, effect: StatusEffect | undefined, cancelled: Utils.BooleanHolder, args: any[]): boolean | Promise<boolean> {
     return false;
   }
 }
@@ -2723,7 +2724,7 @@ export class BlockStatusDamageAbAttr extends AbAttr {
    * @returns Returns true if status damage is blocked
    */
   apply(pokemon: Pokemon, passive: boolean, cancelled: Utils.BooleanHolder, args: any[]): boolean {
-    if (this.effects.includes(pokemon.status?.effect)) {
+    if (pokemon.status && this.effects.includes(pokemon.status.effect)) {
       cancelled.value = true;
       return true;
     }
@@ -2762,7 +2763,7 @@ export class IncrementMovePriorityAbAttr extends AbAttr {
 export class IgnoreContactAbAttr extends AbAttr { }
 
 export class PreWeatherEffectAbAttr extends AbAttr {
-  applyPreWeatherEffect(pokemon: Pokemon, passive: boolean, weather: Weather, cancelled: Utils.BooleanHolder, args: any[]): boolean | Promise<boolean> {
+  applyPreWeatherEffect(pokemon: Pokemon, passive: boolean, weather: Weather | null, cancelled: Utils.BooleanHolder, args: any[]): boolean | Promise<boolean> {
     return false;
   }
 }
@@ -2793,7 +2794,7 @@ export class SuppressWeatherEffectAbAttr extends PreWeatherEffectAbAttr {
   constructor(affectsImmutable?: boolean) {
     super();
 
-    this.affectsImmutable = affectsImmutable;
+    this.affectsImmutable = affectsImmutable!; // TODO: is this bang correct?
   }
 
   applyPreWeatherEffect(pokemon: Pokemon, passive: boolean, weather: Weather, cancelled: Utils.BooleanHolder, args: any[]): boolean {
@@ -2844,7 +2845,7 @@ function getWeatherCondition(...weatherTypes: WeatherType[]): AbAttrCondition {
       return false;
     }
     const weatherType = pokemon.scene.arena.weather?.weatherType;
-    return weatherType && weatherTypes.indexOf(weatherType) > -1;
+    return !!weatherType && weatherTypes.indexOf(weatherType) > -1;
   };
 }
 
@@ -2853,15 +2854,15 @@ function getAnticipationCondition(): AbAttrCondition {
     for (const opponent of pokemon.getOpponents()) {
       for (const move of opponent.moveset) {
         // move is super effective
-        if (move.getMove() instanceof AttackMove && pokemon.getAttackTypeEffectiveness(move.getMove().type, opponent, true) >= 2) {
+        if (move!.getMove() instanceof AttackMove && pokemon.getAttackTypeEffectiveness(move!.getMove().type, opponent, true) >= 2) { // TODO: is this bang correct?
           return true;
         }
         // move is a OHKO
-        if (move.getMove().hasAttr(OneHitKOAttr)) {
+        if (move!.getMove().hasAttr(OneHitKOAttr)) { // TODO: is this bang correct?
           return true;
         }
         // edge case for hidden power, type is computed
-        if (move.getMove().id === Moves.HIDDEN_POWER) {
+        if (move!.getMove().id === Moves.HIDDEN_POWER) { // TODO: is this bang correct?
           const iv_val = Math.floor(((opponent.ivs[Stat.HP] & 1)
               +(opponent.ivs[Stat.ATK] & 1) * 2
               +(opponent.ivs[Stat.DEF] & 1) * 4
@@ -2909,21 +2910,21 @@ export class ForewarnAbAttr extends PostSummonAbAttr {
     let movePower = 0;
     for (const opponent of pokemon.getOpponents()) {
       for (const move of opponent.moveset) {
-        if (move.getMove() instanceof StatusMove) {
+        if (move!.getMove() instanceof StatusMove) { // TODO: is this bang correct?
           movePower = 1;
-        } else if (move.getMove().hasAttr(OneHitKOAttr)) {
+        } else if (move!.getMove().hasAttr(OneHitKOAttr)) { // TODO: is this bang correct?
           movePower = 150;
-        } else if (move.getMove().id === Moves.COUNTER || move.getMove().id === Moves.MIRROR_COAT || move.getMove().id === Moves.METAL_BURST) {
+        } else if (move!.getMove().id === Moves.COUNTER || move!.getMove().id === Moves.MIRROR_COAT || move!.getMove().id === Moves.METAL_BURST) { // TODO: are those bangs correct?
           movePower = 120;
-        } else if (move.getMove().power === -1) {
+        } else if (move!.getMove().power === -1) { // TODO: is this bang correct?
           movePower = 80;
         } else {
-          movePower = move.getMove().power;
+          movePower = move!.getMove().power; // TODO: is this bang correct?
         }
 
         if (movePower > maxPowerSeen) {
           maxPowerSeen = movePower;
-          maxMove = move.getName();
+          maxMove = move!.getName(); // TODO: is this bang correct?
         }
       }
     }
@@ -2984,7 +2985,7 @@ export class PostWeatherLapseAbAttr extends AbAttr {
     this.weatherTypes = weatherTypes;
   }
 
-  applyPostWeatherLapse(pokemon: Pokemon, passive: boolean, weather: Weather, args: any[]): boolean | Promise<boolean> {
+  applyPostWeatherLapse(pokemon: Pokemon, passive: boolean, weather: Weather | null, args: any[]): boolean | Promise<boolean> {
     return false;
   }
 
@@ -3067,7 +3068,7 @@ export class PostTerrainChangeAddBattlerTagAttr extends PostTerrainChangeAbAttr
 function getTerrainCondition(...terrainTypes: TerrainType[]): AbAttrCondition {
   return (pokemon: Pokemon) => {
     const terrainType = pokemon.scene.arena.terrain?.terrainType;
-    return terrainType && terrainTypes.indexOf(terrainType) > -1;
+    return !!terrainType && terrainTypes.indexOf(terrainType) > -1;
   };
 }
 
@@ -3099,7 +3100,7 @@ export class PostTurnStatusHealAbAttr extends PostTurnAbAttr {
    * @returns Returns true if healed from status, false if not
    */
   applyPostTurn(pokemon: Pokemon, passive: boolean, args: any[]): boolean | Promise<boolean> {
-    if (this.effects.includes(pokemon.status?.effect)) {
+    if (pokemon.status && this.effects.includes(pokemon.status.effect)) {
       if (!pokemon.isFullHp()) {
         const scene = pokemon.scene;
         const abilityName = (!passive ? pokemon.getAbility() : pokemon.getPassiveAbility()).name;
@@ -3335,7 +3336,7 @@ export class FetchBallAbAttr extends PostTurnAbAttr {
    */
   applyPostTurn(pokemon: Pokemon, passive: boolean, args: any[]): boolean {
     const lastUsed = pokemon.scene.currentBattle.lastUsedPokeball;
-    if (lastUsed !== null && pokemon.isPlayer) {
+    if (lastUsed !== null && !!pokemon.isPlayer) {
       pokemon.scene.pokeballCounts[lastUsed]++;
       pokemon.scene.currentBattle.lastUsedPokeball = null;
       pokemon.scene.queueMessage(i18next.t("abilityTriggers:fetchBall", { pokemonNameWithAffix: getPokemonNameWithAffix(pokemon), pokeballName: getPokeballName(lastUsed) }));
@@ -3616,7 +3617,8 @@ export class PostBattleLootAbAttr extends PostBattleAbAttr {
     const postBattleLoot = pokemon.scene.currentBattle.postBattleLoot;
     if (postBattleLoot.length) {
       const randItem = Utils.randSeedItem(postBattleLoot);
-      if (pokemon.scene.tryTransferHeldItemModifier(randItem, pokemon, true, 1, true)) {
+      //@ts-ignore - TODO see below
+      if (pokemon.scene.tryTransferHeldItemModifier(randItem, pokemon, true, 1, true)) { // TODO: fix. This is a promise!?
         postBattleLoot.splice(postBattleLoot.indexOf(randItem), 1);
         pokemon.scene.queueMessage(i18next.t("abilityTriggers:postBattleLoot", { pokemonNameWithAffix: getPokemonNameWithAffix(pokemon), itemName: randItem.type.name }));
         return true;
@@ -3648,7 +3650,7 @@ export class PostFaintClearWeatherAbAttr extends PostFaintAbAttr {
    * @returns {boolean} Returns true if the weather clears, otherwise false.
    */
   applyPostFaint(pokemon: Pokemon, passive: boolean, attacker: Pokemon, move: Move, hitResult: HitResult, args: any[]): boolean {
-    const weatherType = pokemon.scene.arena.weather.weatherType;
+    const weatherType = pokemon.scene.arena.weather?.weatherType;
     let turnOffWeather = false;
 
     // Clear weather only if user's ability matches the weather and no other pokemon has the ability.
@@ -4120,7 +4122,7 @@ export class BypassSpeedChanceAbAttr extends AbAttr {
       const turnCommand =
         pokemon.scene.currentBattle.turnCommands[pokemon.getBattlerIndex()];
       const isCommandFight = turnCommand?.command === Command.FIGHT;
-      const move = allMoves[turnCommand.move?.move];
+      const move = turnCommand?.move?.move ?allMoves[turnCommand.move.move] : null;
       const isDamageMove = move?.category === MoveCategory.PHYSICAL || move?.category === MoveCategory.SPECIAL;
 
       if (isCommandFight && isDamageMove) {
@@ -4139,14 +4141,14 @@ export class BypassSpeedChanceAbAttr extends AbAttr {
 
 async function applyAbAttrsInternal<TAttr extends AbAttr>(
   attrType: Constructor<TAttr>,
-  pokemon: Pokemon,
+  pokemon: Pokemon | null,
   applyFunc: AbAttrApplyFunc<TAttr>,
   args: any[],
   showAbilityInstant: boolean = false,
   quiet: boolean = false,
 ) {
   for (const passive of [false, true]) {
-    if (!pokemon.canApplyAbility(passive)) {
+    if (!pokemon?.canApplyAbility(passive)) {
       continue;
     }
 
@@ -4194,7 +4196,7 @@ async function applyAbAttrsInternal<TAttr extends AbAttr>(
   }
 }
 
-export function applyAbAttrs(attrType: Constructor<AbAttr>, pokemon: Pokemon, cancelled: Utils.BooleanHolder, ...args: any[]): Promise<void> {
+export function applyAbAttrs(attrType: Constructor<AbAttr>, pokemon: Pokemon, cancelled: Utils.BooleanHolder | null, ...args: any[]): Promise<void> {
   return applyAbAttrsInternal<AbAttr>(attrType, pokemon, (attr, passive) => attr.apply(pokemon, passive, cancelled, args), args);
 }
 
@@ -4204,13 +4206,13 @@ export function applyPostBattleInitAbAttrs(attrType: Constructor<PostBattleInitA
 }
 
 export function applyPreDefendAbAttrs(attrType: Constructor<PreDefendAbAttr>,
-  pokemon: Pokemon, attacker: Pokemon, move: Move, cancelled: Utils.BooleanHolder, ...args: any[]): Promise<void> {
+  pokemon: Pokemon, attacker: Pokemon, move: Move | null, cancelled: Utils.BooleanHolder | null, ...args: any[]): Promise<void> {
   const simulated = args.length > 1 && args[1];
   return applyAbAttrsInternal<PreDefendAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPreDefend(pokemon, passive, attacker, move, cancelled, args), args, false, simulated);
 }
 
 export function applyPostDefendAbAttrs(attrType: Constructor<PostDefendAbAttr>,
-  pokemon: Pokemon, attacker: Pokemon, move: Move, hitResult: HitResult, ...args: any[]): Promise<void> {
+  pokemon: Pokemon, attacker: Pokemon, move: Move, hitResult: HitResult | null, ...args: any[]): Promise<void> {
   return applyAbAttrsInternal<PostDefendAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPostDefend(pokemon, passive, attacker, move, hitResult, args), args);
 }
 
@@ -4240,12 +4242,12 @@ export function applyFieldBattleStatMultiplierAbAttrs(attrType: Constructor<Fiel
 }
 
 export function applyPreAttackAbAttrs(attrType: Constructor<PreAttackAbAttr>,
-  pokemon: Pokemon, defender: Pokemon, move: Move, ...args: any[]): Promise<void> {
+  pokemon: Pokemon, defender: Pokemon | null, move: Move, ...args: any[]): Promise<void> {
   return applyAbAttrsInternal<PreAttackAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPreAttack(pokemon, passive, defender, move, args), args);
 }
 
 export function applyPostAttackAbAttrs(attrType: Constructor<PostAttackAbAttr>,
-  pokemon: Pokemon, defender: Pokemon, move: Move, hitResult: HitResult, ...args: any[]): Promise<void> {
+  pokemon: Pokemon, defender: Pokemon, move: Move, hitResult: HitResult | null, ...args: any[]): Promise<void> {
   return applyAbAttrsInternal<PostAttackAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPostAttack(pokemon, passive, defender, move, hitResult, args), args);
 }
 
@@ -4270,7 +4272,7 @@ export function applyPreSwitchOutAbAttrs(attrType: Constructor<PreSwitchOutAbAtt
 }
 
 export function applyPreStatChangeAbAttrs(attrType: Constructor<PreStatChangeAbAttr>,
-  pokemon: Pokemon, stat: BattleStat, cancelled: Utils.BooleanHolder, ...args: any[]): Promise<void> {
+  pokemon: Pokemon | null, stat: BattleStat, cancelled: Utils.BooleanHolder, ...args: any[]): Promise<void> {
   return applyAbAttrsInternal<PreStatChangeAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPreStatChange(pokemon, passive, stat, cancelled, args), args);
 }
 
@@ -4280,7 +4282,7 @@ export function applyPostStatChangeAbAttrs(attrType: Constructor<PostStatChangeA
 }
 
 export function applyPreSetStatusAbAttrs(attrType: Constructor<PreSetStatusAbAttr>,
-  pokemon: Pokemon, effect: StatusEffect, cancelled: Utils.BooleanHolder, ...args: any[]): Promise<void> {
+  pokemon: Pokemon, effect: StatusEffect | undefined, cancelled: Utils.BooleanHolder, ...args: any[]): Promise<void> {
   const simulated = args.length > 1 && args[1];
   return applyAbAttrsInternal<PreSetStatusAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPreSetStatus(pokemon, passive, effect, cancelled, args), args, false, !simulated);
 }
@@ -4291,7 +4293,7 @@ export function applyPreApplyBattlerTagAbAttrs(attrType: Constructor<PreApplyBat
 }
 
 export function applyPreWeatherEffectAbAttrs(attrType: Constructor<PreWeatherEffectAbAttr>,
-  pokemon: Pokemon, weather: Weather, cancelled: Utils.BooleanHolder, ...args: any[]): Promise<void> {
+  pokemon: Pokemon, weather: Weather | null, cancelled: Utils.BooleanHolder, ...args: any[]): Promise<void> {
   return applyAbAttrsInternal<PreWeatherDamageAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPreWeatherEffect(pokemon, passive, weather, cancelled, args), args, true);
 }
 
@@ -4306,7 +4308,7 @@ export function applyPostWeatherChangeAbAttrs(attrType: Constructor<PostWeatherC
 }
 
 export function applyPostWeatherLapseAbAttrs(attrType: Constructor<PostWeatherLapseAbAttr>,
-  pokemon: Pokemon, weather: Weather, ...args: any[]): Promise<void> {
+  pokemon: Pokemon, weather: Weather | null, ...args: any[]): Promise<void> {
   return applyAbAttrsInternal<PostWeatherLapseAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPostWeatherLapse(pokemon, passive, weather, args), args);
 }
 
@@ -4595,8 +4597,8 @@ export function initAbilities() {
       .attr(TypeImmunityStatChangeAbAttr, Type.ELECTRIC, BattleStat.SPD, 1)
       .ignorable(),
     new Ability(Abilities.RIVALRY, 4)
-      .attr(MovePowerBoostAbAttr, (user, target, move) => user.gender !== Gender.GENDERLESS && target.gender !== Gender.GENDERLESS && user.gender === target.gender, 1.25, true)
-      .attr(MovePowerBoostAbAttr, (user, target, move) => user.gender !== Gender.GENDERLESS && target.gender !== Gender.GENDERLESS && user.gender !== target.gender, 0.75),
+      .attr(MovePowerBoostAbAttr, (user, target, move) => user?.gender !== Gender.GENDERLESS && target?.gender !== Gender.GENDERLESS && user?.gender === target?.gender, 1.25, true)
+      .attr(MovePowerBoostAbAttr, (user, target, move) => user?.gender !== Gender.GENDERLESS && target?.gender !== Gender.GENDERLESS && user?.gender !== target?.gender, 0.75),
     new Ability(Abilities.STEADFAST, 4)
       .attr(FlinchStatChangeAbAttr, BattleStat.SPD, 1),
     new Ability(Abilities.SNOW_CLOAK, 4)
@@ -4686,7 +4688,8 @@ export function initAbilities() {
       .attr(IgnoreOpponentStatChangesAbAttr)
       .ignorable(),
     new Ability(Abilities.TINTED_LENS, 4)
-      .attr(DamageBoostAbAttr, 2, (user, target, move) => target.getAttackTypeEffectiveness(move.type, user) <= 0.5),
+      //@ts-ignore
+      .attr(DamageBoostAbAttr, 2, (user, target, move) => target.getAttackTypeEffectiveness(move.type, user) <= 0.5), // TODO: fix TS issues
     new Ability(Abilities.FILTER, 4)
       .attr(ReceivedMoveDamageMultiplierAbAttr,(target, user, move) => target.getAttackTypeEffectiveness(move.type, user) >= 2, 0.75)
       .ignorable(),
@@ -4768,9 +4771,9 @@ export function initAbilities() {
       .attr(ReceivedMoveDamageMultiplierAbAttr,(target, user, move) => target.isFullHp(), 0.5)
       .ignorable(),
     new Ability(Abilities.TOXIC_BOOST, 5)
-      .attr(MovePowerBoostAbAttr, (user, target, move) => move.category === MoveCategory.PHYSICAL && (user.status?.effect === StatusEffect.POISON || user.status?.effect === StatusEffect.TOXIC), 1.5),
+      .attr(MovePowerBoostAbAttr, (user, target, move) => move.category === MoveCategory.PHYSICAL && (user?.status?.effect === StatusEffect.POISON || user?.status?.effect === StatusEffect.TOXIC), 1.5),
     new Ability(Abilities.FLARE_BOOST, 5)
-      .attr(MovePowerBoostAbAttr, (user, target, move) => move.category === MoveCategory.SPECIAL && user.status?.effect === StatusEffect.BURN, 1.5),
+      .attr(MovePowerBoostAbAttr, (user, target, move) => move.category === MoveCategory.SPECIAL && user?.status?.effect === StatusEffect.BURN, 1.5),
     new Ability(Abilities.HARVEST, 5)
       .attr(
         PostTurnLootAbAttr,
@@ -4803,7 +4806,8 @@ export function initAbilities() {
       .attr(WonderSkinAbAttr)
       .ignorable(),
     new Ability(Abilities.ANALYTIC, 5)
-      .attr(MovePowerBoostAbAttr, (user, target, move) => !!target.getLastXMoves(1).find(m => m.turn === target.scene.currentBattle.turn) || user.scene.currentBattle.turnCommands[target.getBattlerIndex()].command !== Command.FIGHT, 1.3),
+    //@ts-ignore
+      .attr(MovePowerBoostAbAttr, (user, target, move) => !!target?.getLastXMoves(1).find(m => m.turn === target?.scene.currentBattle.turn) || user.scene.currentBattle.turnCommands[target.getBattlerIndex()].command !== Command.FIGHT, 1.3), // TODO fix TS issues
     new Ability(Abilities.ILLUSION, 5)
       .attr(UncopiableAbilityAbAttr)
       .attr(UnswappableAbilityAbAttr)
@@ -4953,7 +4957,7 @@ export function initAbilities() {
     new Ability(Abilities.WATER_COMPACTION, 7)
       .attr(PostDefendStatChangeAbAttr, (target, user, move) => move.type === Type.WATER && move.category !== MoveCategory.STATUS, BattleStat.DEF, 2),
     new Ability(Abilities.MERCILESS, 7)
-      .attr(ConditionalCritAbAttr, (user, target, move) => target.status?.effect === StatusEffect.TOXIC || target.status?.effect === StatusEffect.POISON),
+      .attr(ConditionalCritAbAttr, (user, target, move) => target?.status?.effect === StatusEffect.TOXIC || target?.status?.effect === StatusEffect.POISON),
     new Ability(Abilities.SHIELDS_DOWN, 7)
       .attr(PostBattleInitFormChangeAbAttr, () => 0)
       .attr(PostSummonFormChangeAbAttr, p => p.formIndex % 7 + (p.getHpRatio() <= 0.5 ? 7 : 0))
@@ -4965,7 +4969,8 @@ export function initAbilities() {
       .bypassFaint()
       .partial(),
     new Ability(Abilities.STAKEOUT, 7)
-      .attr(MovePowerBoostAbAttr, (user, target, move) => user.scene.currentBattle.turnCommands[target.getBattlerIndex()].command === Command.POKEMON, 2),
+      //@ts-ignore
+      .attr(MovePowerBoostAbAttr, (user, target, move) => user.scene.currentBattle.turnCommands[target.getBattlerIndex()].command === Command.POKEMON, 2), // TODO: fix TS issues
     new Ability(Abilities.WATER_BUBBLE, 7)
       .attr(ReceivedTypeDamageMultiplierAbAttr, Type.FIRE, 0.5)
       .attr(MoveTypePowerBoostAbAttr, Type.WATER, 2)
@@ -5105,7 +5110,8 @@ export function initAbilities() {
     new Ability(Abilities.PRISM_ARMOR, 7)
       .attr(ReceivedMoveDamageMultiplierAbAttr,(target, user, move) => target.getAttackTypeEffectiveness(move.type, user) >= 2, 0.75),
     new Ability(Abilities.NEUROFORCE, 7)
-      .attr(MovePowerBoostAbAttr, (user, target, move) => target.getAttackTypeEffectiveness(move.type, user) >= 2, 1.25),
+      //@ts-ignore
+      .attr(MovePowerBoostAbAttr, (user, target, move) => target.getAttackTypeEffectiveness(move.type, user) >= 2, 1.25), // TODO: fix TS issues
     new Ability(Abilities.INTREPID_SWORD, 8)
       .attr(PostSummonStatChangeAbAttr, BattleStat.ATK, 1, true)
       .condition(getOncePerBattleCondition(Abilities.INTREPID_SWORD)),
@@ -5192,8 +5198,10 @@ export function initAbilities() {
       .attr(UserFieldStatusEffectImmunityAbAttr, StatusEffect.POISON, StatusEffect.TOXIC)
       .ignorable(),
     new Ability(Abilities.HUNGER_SWITCH, 8)
-      .attr(PostTurnFormChangeAbAttr, p => p.getFormKey ? 0 : 1)
-      .attr(PostTurnFormChangeAbAttr, p => p.getFormKey ? 1 : 0)
+      //@ts-ignore
+      .attr(PostTurnFormChangeAbAttr, p => p.getFormKey ? 0 : 1) // TODO: fix ts-ignore
+      //@ts-ignore
+      .attr(PostTurnFormChangeAbAttr, p => p.getFormKey ? 1 : 0) // TODO: fix ts-ignore
       .attr(UncopiableAbilityAbAttr)
       .attr(UnswappableAbilityAbAttr)
       .attr(NoTransformAbilityAbAttr)
diff --git a/src/data/arena-tag.ts b/src/data/arena-tag.ts
index 9c846d2f3cb..7c67271b0dc 100644
--- a/src/data/arena-tag.ts
+++ b/src/data/arena-tag.ts
@@ -25,12 +25,12 @@ export enum ArenaTagSide {
 export abstract class ArenaTag {
   public tagType: ArenaTagType;
   public turnCount: integer;
-  public sourceMove: Moves;
-  public sourceId: integer;
+  public sourceMove?: Moves;
+  public sourceId?: integer;
   public side: ArenaTagSide;
 
 
-  constructor(tagType: ArenaTagType, turnCount: integer, sourceMove: Moves, sourceId?: integer, side: ArenaTagSide = ArenaTagSide.BOTH) {
+  constructor(tagType: ArenaTagType, turnCount: integer, sourceMove: Moves | undefined, sourceId?: integer, side: ArenaTagSide = ArenaTagSide.BOTH) {
     this.tagType = tagType;
     this.turnCount = turnCount;
     this.sourceMove = sourceMove;
@@ -56,7 +56,7 @@ export abstract class ArenaTag {
     return this.turnCount < 1 || !!(--this.turnCount);
   }
 
-  getMoveName(): string {
+  getMoveName(): string | null {
     return this.sourceMove
       ? allMoves[this.sourceMove].name
       : null;
@@ -75,9 +75,14 @@ export class MistTag extends ArenaTag {
   onAdd(arena: Arena, quiet: boolean = false): void {
     super.onAdd(arena);
 
-    const source = arena.scene.getPokemonById(this.sourceId);
-    if (!quiet) {
-      arena.scene.queueMessage(i18next.t("arenaTag:mistOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(source) }));
+    if (this.sourceId) {
+      const source = arena.scene.getPokemonById(this.sourceId);
+
+      if (!quiet && source) {
+        arena.scene.queueMessage(i18next.t("arenaTag:mistOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(source) }));
+      } else if (!quiet) {
+        console.warn("Failed to get source for MistTag onAdd");
+      }
     }
   }
 
@@ -280,8 +285,14 @@ class MatBlockTag extends ConditionalProtectTag {
   }
 
   onAdd(arena: Arena) {
-    const source = arena.scene.getPokemonById(this.sourceId);
-    arena.scene.queueMessage(i18next.t("arenaTag:matBlockOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(source) }));
+    if (this.sourceId) {
+      const source = arena.scene.getPokemonById(this.sourceId);
+      if (source) {
+        arena.scene.queueMessage(i18next.t("arenaTag:matBlockOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(source) }));
+      } else {
+        console.warn("Failed to get source for MatBlockTag onAdd");
+      }
+    }
   }
 }
 
@@ -328,9 +339,9 @@ export class NoCritTag extends ArenaTag {
 
   /** Queues a message upon removing this effect from the field */
   onRemove(arena: Arena): void {
-    const source = arena.scene.getPokemonById(this.sourceId);
+    const source = arena.scene.getPokemonById(this.sourceId!); // TODO: is this bang correct?
     arena.scene.queueMessage(i18next.t("arenaTag:noCritOnRemove", {
-      pokemonNameWithAffix: getPokemonNameWithAffix(source),
+      pokemonNameWithAffix: getPokemonNameWithAffix(source ?? undefined),
       moveName: this.getMoveName()
     }));
   }
@@ -350,10 +361,16 @@ class WishTag extends ArenaTag {
   }
 
   onAdd(arena: Arena): void {
-    const user = arena.scene.getPokemonById(this.sourceId);
-    this.battlerIndex = user.getBattlerIndex();
-    this.triggerMessage = i18next.t("arenaTag:wishTagOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(user) });
-    this.healHp = Math.max(Math.floor(user.getMaxHp() / 2), 1);
+    if (this.sourceId) {
+      const user = arena.scene.getPokemonById(this.sourceId);
+      if (user) {
+        this.battlerIndex = user.getBattlerIndex();
+        this.triggerMessage = i18next.t("arenaTag:wishTagOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(user) });
+        this.healHp = Math.max(Math.floor(user.getMaxHp() / 2), 1);
+      } else {
+        console.warn("Failed to get source for WishTag onAdd");
+      }
+    }
   }
 
   onRemove(arena: Arena): void {
@@ -494,8 +511,8 @@ class SpikesTag extends ArenaTrapTag {
   onAdd(arena: Arena, quiet: boolean = false): void {
     super.onAdd(arena);
 
-    const source = arena.scene.getPokemonById(this.sourceId);
-    if (!quiet) {
+    const source = this.sourceId ? arena.scene.getPokemonById(this.sourceId) : null;
+    if (!quiet && source) {
       arena.scene.queueMessage(i18next.t("arenaTag:spikesOnAdd", { moveName: this.getMoveName(), opponentDesc: source.getOpponentDescriptor() }));
     }
   }
@@ -539,8 +556,8 @@ class ToxicSpikesTag extends ArenaTrapTag {
   onAdd(arena: Arena, quiet: boolean = false): void {
     super.onAdd(arena);
 
-    const source = arena.scene.getPokemonById(this.sourceId);
-    if (!quiet) {
+    const source = this.sourceId ? arena.scene.getPokemonById(this.sourceId) : null;
+    if (!quiet && source) {
       arena.scene.queueMessage(i18next.t("arenaTag:toxicSpikesOnAdd", { moveName: this.getMoveName(), opponentDesc: source.getOpponentDescriptor() }));
     }
   }
@@ -589,7 +606,7 @@ class ToxicSpikesTag extends ArenaTrapTag {
 class DelayedAttackTag extends ArenaTag {
   public targetIndex: BattlerIndex;
 
-  constructor(tagType: ArenaTagType, sourceMove: Moves, sourceId: integer, targetIndex: BattlerIndex) {
+  constructor(tagType: ArenaTagType, sourceMove: Moves | undefined, sourceId: integer, targetIndex: BattlerIndex) {
     super(tagType, 3, sourceMove, sourceId);
 
     this.targetIndex = targetIndex;
@@ -599,7 +616,7 @@ class DelayedAttackTag extends ArenaTag {
     const ret = super.lapse(arena);
 
     if (!ret) {
-      arena.scene.unshiftPhase(new MoveEffectPhase(arena.scene, this.sourceId, [ this.targetIndex ], new PokemonMove(this.sourceMove, 0, 0, true)));
+      arena.scene.unshiftPhase(new MoveEffectPhase(arena.scene, this.sourceId!, [ this.targetIndex ], new PokemonMove(this.sourceMove!, 0, 0, true))); // TODO: are those bangs correct?
     }
 
     return ret;
@@ -621,8 +638,8 @@ class StealthRockTag extends ArenaTrapTag {
   onAdd(arena: Arena, quiet: boolean = false): void {
     super.onAdd(arena);
 
-    const source = arena.scene.getPokemonById(this.sourceId);
-    if (!quiet) {
+    const source = this.sourceId ? arena.scene.getPokemonById(this.sourceId) : null;
+    if (!quiet && source) {
       arena.scene.queueMessage(i18next.t("arenaTag:stealthRockOnAdd", { opponentDesc: source.getOpponentDescriptor() }));
     }
   }
@@ -630,7 +647,7 @@ class StealthRockTag extends ArenaTrapTag {
   getDamageHpRatio(pokemon: Pokemon): number {
     const effectiveness = pokemon.getAttackTypeEffectiveness(Type.ROCK, undefined, true);
 
-    let damageHpRatio: number;
+    let damageHpRatio: number = 0;
 
     switch (effectiveness) {
     case 0:
@@ -696,8 +713,8 @@ class StickyWebTag extends ArenaTrapTag {
 
   onAdd(arena: Arena, quiet: boolean = false): void {
     super.onAdd(arena);
-    const source = arena.scene.getPokemonById(this.sourceId);
-    if (!quiet) {
+    const source = this.sourceId ? arena.scene.getPokemonById(this.sourceId) : null;
+    if (!quiet && source) {
       arena.scene.queueMessage(i18next.t("arenaTag:stickyWebOnAdd", { moveName: this.getMoveName(), opponentDesc: source.getOpponentDescriptor() }));
     }
   }
@@ -735,7 +752,10 @@ export class TrickRoomTag extends ArenaTag {
   }
 
   onAdd(arena: Arena): void {
-    arena.scene.queueMessage(i18next.t("arenaTag:trickRoomOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(arena.scene.getPokemonById(this.sourceId)) }));
+    const source = this.sourceId ? arena.scene.getPokemonById(this.sourceId) : null;
+    if (source) {
+      arena.scene.queueMessage(i18next.t("arenaTag:trickRoomOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(source) }));
+    }
   }
 
   onRemove(arena: Arena): void {
@@ -782,8 +802,8 @@ class TailwindTag extends ArenaTag {
       arena.scene.queueMessage(i18next.t(`arenaTag:tailwindOnAdd${this.side === ArenaTagSide.PLAYER ? "Player" : this.side === ArenaTagSide.ENEMY ? "Enemy" : ""}`));
     }
 
-    const source = arena.scene.getPokemonById(this.sourceId);
-    const party = source.isPlayer() ? source.scene.getPlayerField() : source.scene.getEnemyField();
+    const source = arena.scene.getPokemonById(this.sourceId!); //TODO: this bang is questionable!
+    const party = (source?.isPlayer() ? source.scene.getPlayerField() : source?.scene.getEnemyField()) ?? [];
 
     for (const pokemon of party) {
       // Apply the CHARGED tag to party members with the WIND_POWER ability
@@ -824,7 +844,7 @@ class HappyHourTag extends ArenaTag {
   }
 }
 
-export function getArenaTag(tagType: ArenaTagType, turnCount: integer, sourceMove: Moves, sourceId: integer, targetIndex?: BattlerIndex, side: ArenaTagSide = ArenaTagSide.BOTH): ArenaTag {
+export function getArenaTag(tagType: ArenaTagType, turnCount: integer, sourceMove: Moves | undefined, sourceId: integer, targetIndex?: BattlerIndex, side: ArenaTagSide = ArenaTagSide.BOTH): ArenaTag | null {
   switch (tagType) {
   case ArenaTagType.MIST:
     return new MistTag(turnCount, sourceId, side);
@@ -837,7 +857,7 @@ export function getArenaTag(tagType: ArenaTagType, turnCount: integer, sourceMov
   case ArenaTagType.CRAFTY_SHIELD:
     return new CraftyShieldTag(sourceId, side);
   case ArenaTagType.NO_CRIT:
-    return new NoCritTag(turnCount, sourceMove, sourceId, side);
+    return new NoCritTag(turnCount, sourceMove!, sourceId, side); // TODO: is this bang correct?
   case ArenaTagType.MUD_SPORT:
     return new MudSportTag(turnCount, sourceId);
   case ArenaTagType.WATER_SPORT:
@@ -848,7 +868,7 @@ export function getArenaTag(tagType: ArenaTagType, turnCount: integer, sourceMov
     return new ToxicSpikesTag(sourceId, side);
   case ArenaTagType.FUTURE_SIGHT:
   case ArenaTagType.DOOM_DESIRE:
-    return new DelayedAttackTag(tagType, sourceMove, sourceId, targetIndex);
+    return new DelayedAttackTag(tagType, sourceMove, sourceId, targetIndex!); // TODO:questionable bang
   case ArenaTagType.WISH:
     return new WishTag(turnCount, sourceId, side);
   case ArenaTagType.STEALTH_ROCK:
@@ -869,5 +889,7 @@ export function getArenaTag(tagType: ArenaTagType, turnCount: integer, sourceMov
     return new TailwindTag(turnCount, sourceId, side);
   case ArenaTagType.HAPPY_HOUR:
     return new HappyHourTag(turnCount, sourceId, side);
+  default:
+    return null;
   }
 }
diff --git a/src/data/battle-anims.ts b/src/data/battle-anims.ts
index d4dbb8ec350..d9fc87c67c7 100644
--- a/src/data/battle-anims.ts
+++ b/src/data/battle-anims.ts
@@ -128,7 +128,7 @@ export class AnimConfig {
       for (const fte of Object.keys(frameTimedEvents)) {
         const timedEvents: AnimTimedEvent[] = [];
         for (const te of frameTimedEvents[fte]) {
-          let timedEvent: AnimTimedEvent;
+          let timedEvent: AnimTimedEvent | undefined;
           switch (te.eventType) {
           case "AnimTimedSoundEvent":
             timedEvent = new AnimTimedSoundEvent(te.frameIndex, te.resourceName, te);
@@ -140,7 +140,8 @@ export class AnimConfig {
             timedEvent = new AnimTimedUpdateBgEvent(te.frameIndex, te.resourceName, te);
             break;
           }
-          timedEvents.push(timedEvent);
+
+          timedEvent && timedEvents.push(timedEvent);
         }
         this.frameTimedEvents.set(parseInt(fte), timedEvents);
       }
@@ -330,7 +331,7 @@ class AnimTimedSoundEvent extends AnimTimedEvent {
       }
       return Math.ceil((scene.sound.get(this.resourceName).totalDuration * 1000) / 33.33);
     } else {
-      return Math.ceil((battleAnim.user.cry(soundConfig).totalDuration * 1000) / 33.33);
+      return Math.ceil((battleAnim.user!.cry(soundConfig).totalDuration * 1000) / 33.33); // TODO: is the bang behind user correct?
     }
   }
 
@@ -441,15 +442,15 @@ class AnimTimedAddBgEvent extends AnimTimedBgEvent {
   }
 }
 
-export const moveAnims = new Map<Moves, AnimConfig | [AnimConfig, AnimConfig]>();
-export const chargeAnims = new Map<ChargeAnim, AnimConfig | [AnimConfig, AnimConfig]>();
+export const moveAnims = new Map<Moves, AnimConfig | [AnimConfig, AnimConfig] | null>();
+export const chargeAnims = new Map<ChargeAnim, AnimConfig | [AnimConfig, AnimConfig] | null>();
 export const commonAnims = new Map<CommonAnim, AnimConfig>();
 
 export function initCommonAnims(scene: BattleScene): Promise<void> {
   return new Promise(resolve => {
     const commonAnimNames = Utils.getEnumKeys(CommonAnim);
     const commonAnimIds = Utils.getEnumValues(CommonAnim);
-    const commonAnimFetches = [];
+    const commonAnimFetches: Promise<Map<CommonAnim, AnimConfig>>[] = [];
     for (let ca = 0; ca < commonAnimIds.length; ca++) {
       const commonAnimId = commonAnimIds[ca];
       commonAnimFetches.push(scene.cachedFetch(`./battle-anims/common-${commonAnimNames[ca].toLowerCase().replace(/\_/g, "-")}.json`)
@@ -572,7 +573,7 @@ export function loadMoveAnimAssets(scene: BattleScene, moveIds: Moves[], startLo
       const chargeAttr = allMoves[moveId].getAttrs(ChargeAttr)[0] || allMoves[moveId].getAttrs(DelayedAttackAttr)[0];
       if (chargeAttr) {
         const moveChargeAnims = chargeAnims.get(chargeAttr.chargeAnim);
-        moveAnimations.push(moveChargeAnims instanceof AnimConfig ? moveChargeAnims : moveChargeAnims[0]);
+        moveAnimations.push(moveChargeAnims instanceof AnimConfig ? moveChargeAnims : moveChargeAnims![0]); // TODO: is the bang correct?
         if (Array.isArray(moveChargeAnims)) {
           moveAnimations.push(moveChargeAnims[1]);
         }
@@ -668,21 +669,21 @@ interface SpriteCache {
 }
 
 export abstract class BattleAnim {
-  public user: Pokemon;
-  public target: Pokemon;
+  public user: Pokemon | null;
+  public target: Pokemon | null;
   public sprites: Phaser.GameObjects.Sprite[];
   public bgSprite: Phaser.GameObjects.TileSprite | Phaser.GameObjects.Rectangle;
 
   private srcLine: number[];
   private dstLine: number[];
 
-  constructor(user: Pokemon, target: Pokemon) {
-    this.user = user;
-    this.target = target;
+  constructor(user?: Pokemon, target?: Pokemon) {
+    this.user = user!; // TODO: is this bang correct?
+    this.target = target!; // TODO: is this bang correct?
     this.sprites = [];
   }
 
-    abstract getAnim(): AnimConfig;
+    abstract getAnim(): AnimConfig | null;
 
     abstract isOppAnim(): boolean;
 
@@ -705,12 +706,12 @@ export abstract class BattleAnim {
       const user = !isOppAnim ? this.user : this.target;
       const target = !isOppAnim ? this.target : this.user;
 
-      const userInitialX = user.x;
-      const userInitialY = user.y;
-      const userHalfHeight = user.getSprite().displayHeight / 2;
-      const targetInitialX = target.x;
-      const targetInitialY = target.y;
-      const targetHalfHeight = target.getSprite().displayHeight / 2;
+      const userInitialX = user!.x; // TODO: is this bang correct?
+      const userInitialY = user!.y; // TODO: is this bang correct?
+      const userHalfHeight = user!.getSprite().displayHeight! / 2; // TODO: is this bang correct?
+      const targetInitialX = target!.x; // TODO: is this bang correct?
+      const targetInitialY = target!.y; // TODO: is this bang correct?
+      const targetHalfHeight = target!.getSprite().displayHeight! / 2; // TODO: is this bang correct?
 
       let g = 0;
       let u = 0;
@@ -742,7 +743,7 @@ export abstract class BattleAnim {
         }
         const angle = -frame.angle;
         const key = frame.target === AnimFrameTarget.GRAPHIC ? g++ : frame.target === AnimFrameTarget.USER ? u++ : t++;
-        ret.get(frame.target).set(key, { x: x, y: y, scaleX: scaleX, scaleY: scaleY, angle: angle });
+        ret.get(frame.target)!.set(key, { x: x, y: y, scaleX: scaleX, scaleY: scaleY, angle: angle }); // TODO: is the bang correct?
       }
 
       return ret;
@@ -750,10 +751,10 @@ export abstract class BattleAnim {
 
     play(scene: BattleScene, callback?: Function) {
       const isOppAnim = this.isOppAnim();
-      const user = !isOppAnim ? this.user : this.target;
+      const user = !isOppAnim ? this.user! : this.target!; // TODO: are those bangs correct?
       const target = !isOppAnim ? this.target : this.user;
 
-      if (!target.isOnField()) {
+      if (!target?.isOnField()) {
         if (callback) {
           callback();
         }
@@ -781,7 +782,7 @@ export abstract class BattleAnim {
         targetSprite.setAlpha(1);
         targetSprite.pipelineData["tone"] = [ 0.0, 0.0, 0.0, 0.0 ];
         targetSprite.setAngle(0);
-        if (!this.isHideUser()) {
+        if (!this.isHideUser() && userSprite) {
           userSprite.setVisible(true);
         }
         if (!this.isHideTarget() && (targetSprite !== userSprite || !this.isHideUser())) {
@@ -814,20 +815,20 @@ export abstract class BattleAnim {
       this.srcLine = [ userFocusX, userFocusY, targetFocusX, targetFocusY ];
       this.dstLine = [ userInitialX, userInitialY, targetInitialX, targetInitialY ];
 
-      let r = anim.frames.length;
+      let r = anim!.frames.length; // TODO: is this bang correct?
       let f = 0;
 
       scene.tweens.addCounter({
         duration: Utils.getFrameMs(3),
-        repeat: anim.frames.length,
+        repeat: anim!.frames.length, // TODO: is this bang correct?
         onRepeat: () => {
           if (!f) {
             userSprite.setVisible(false);
             targetSprite.setVisible(false);
           }
 
-          const spriteFrames = anim.frames[f];
-          const frameData = this.getGraphicFrameData(scene, anim.frames[f]);
+          const spriteFrames = anim!.frames[f]; // TODO: is the bang correcT?
+          const frameData = this.getGraphicFrameData(scene, anim!.frames[f]); // TODO: is the bang correct?
           let u = 0;
           let t = 0;
           let g = 0;
@@ -840,9 +841,9 @@ export abstract class BattleAnim {
               const sprites = spriteCache[isUser ? AnimFrameTarget.USER : AnimFrameTarget.TARGET];
               const spriteSource = isUser ? userSprite : targetSprite;
               if ((isUser ? u : t) === sprites.length) {
-                const sprite = scene.addPokemonSprite(isUser ? user : target, 0, 0, spriteSource.texture, spriteSource.frame.name, true);
-                [ "spriteColors", "fusionSpriteColors" ].map(k => sprite.pipelineData[k] = (isUser ? user : target).getSprite().pipelineData[k]);
-                sprite.setPipelineData("spriteKey", (isUser ? user : target).getBattleSpriteKey());
+                const sprite = scene.addPokemonSprite(isUser ? user! : target, 0, 0, spriteSource!.texture, spriteSource!.frame.name, true); // TODO: are those bangs correct?
+                [ "spriteColors", "fusionSpriteColors" ].map(k => sprite.pipelineData[k] = (isUser ? user! : target).getSprite().pipelineData[k]); // TODO: are those bangs correct?
+                sprite.setPipelineData("spriteKey", (isUser ? user! : target).getBattleSpriteKey());
                 sprite.setPipelineData("shiny", (isUser ? user : target).shiny);
                 sprite.setPipelineData("variant", (isUser ? user : target).variant);
                 sprite.setPipelineData("ignoreFieldPos", true);
@@ -853,7 +854,7 @@ export abstract class BattleAnim {
 
               const spriteIndex = isUser ? u++ : t++;
               const pokemonSprite = sprites[spriteIndex];
-              const graphicFrameData = frameData.get(frame.target).get(spriteIndex);
+              const graphicFrameData = frameData.get(frame.target)!.get(spriteIndex)!; // TODO: are the bangs correct?
               pokemonSprite.setPosition(graphicFrameData.x, graphicFrameData.y - ((spriteSource.height / 2) * (spriteSource.parentContainer.scale - 1)));
 
               pokemonSprite.setAngle(graphicFrameData.angle);
@@ -868,7 +869,7 @@ export abstract class BattleAnim {
             } else {
               const sprites = spriteCache[AnimFrameTarget.GRAPHIC];
               if (g === sprites.length) {
-                const newSprite: Phaser.GameObjects.Sprite = scene.addFieldSprite(0, 0, anim.graphic, 1);
+                const newSprite: Phaser.GameObjects.Sprite = scene.addFieldSprite(0, 0, anim!.graphic, 1); // TODO: is the bang correct?
                 sprites.push(newSprite);
                 scene.field.add(newSprite);
                 spritePriorities.push(1);
@@ -881,7 +882,7 @@ export abstract class BattleAnim {
                 const setSpritePriority = (priority: integer) => {
                   switch (priority) {
                   case 0:
-                    scene.field.moveBelow(moveSprite as Phaser.GameObjects.GameObject, scene.getEnemyPokemon() || scene.getPlayerPokemon());
+                    scene.field.moveBelow(moveSprite as Phaser.GameObjects.GameObject, scene.getEnemyPokemon() || scene.getPlayerPokemon()!); // TODO: is this bang correct?
                     break;
                   case 1:
                     scene.field.moveTo(moveSprite, scene.field.getAll().length - 1);
@@ -892,11 +893,11 @@ export abstract class BattleAnim {
                       if (this.bgSprite) {
                         scene.field.moveAbove(moveSprite as Phaser.GameObjects.GameObject, this.bgSprite);
                       } else {
-                        scene.field.moveBelow(moveSprite as Phaser.GameObjects.GameObject, this.user);
+                        scene.field.moveBelow(moveSprite as Phaser.GameObjects.GameObject, this.user!); // TODO: is this bang correct?
                       }
                       break;
                     case AnimFocus.TARGET:
-                      scene.field.moveBelow(moveSprite as Phaser.GameObjects.GameObject, this.target);
+                      scene.field.moveBelow(moveSprite as Phaser.GameObjects.GameObject, this.target!); // TODO: is this bang correct?
                       break;
                     default:
                       setSpritePriority(1);
@@ -906,10 +907,10 @@ export abstract class BattleAnim {
                   case 3:
                     switch (frame.focus) {
                     case AnimFocus.USER:
-                      scene.field.moveAbove(moveSprite as Phaser.GameObjects.GameObject, this.user);
+                      scene.field.moveAbove(moveSprite as Phaser.GameObjects.GameObject, this.user!); // TODO: is this bang correct?
                       break;
                     case AnimFocus.TARGET:
-                      scene.field.moveAbove(moveSprite as Phaser.GameObjects.GameObject, this.target);
+                      scene.field.moveAbove(moveSprite as Phaser.GameObjects.GameObject, this.target!); // TODO: is this bang correct?
                       break;
                     default:
                       setSpritePriority(1);
@@ -925,7 +926,7 @@ export abstract class BattleAnim {
               moveSprite.setFrame(frame.graphicFrame);
               //console.log(AnimFocus[frame.focus]);
 
-              const graphicFrameData = frameData.get(frame.target).get(graphicIndex);
+              const graphicFrameData = frameData.get(frame.target)!.get(graphicIndex)!; // TODO: are those bangs correct?
               moveSprite.setPosition(graphicFrameData.x, graphicFrameData.y);
               moveSprite.setAngle(graphicFrameData.angle);
               moveSprite.setScale(graphicFrameData.scaleX,  graphicFrameData.scaleY);
@@ -935,8 +936,8 @@ export abstract class BattleAnim {
               moveSprite.setBlendMode(frame.blendType === AnimBlendType.NORMAL ? Phaser.BlendModes.NORMAL : frame.blendType === AnimBlendType.ADD ? Phaser.BlendModes.ADD : Phaser.BlendModes.DIFFERENCE);
             }
           }
-          if (anim.frameTimedEvents.has(f)) {
-            for (const event of anim.frameTimedEvents.get(f)) {
+          if (anim?.frameTimedEvents.has(f)) {
+            for (const event of anim.frameTimedEvents.get(f)!) { // TODO: is this bang correct?
               r = Math.max((anim.frames.length - f) + event.execute(scene, this), r);
             }
           }
@@ -980,16 +981,16 @@ export abstract class BattleAnim {
 }
 
 export class CommonBattleAnim extends BattleAnim {
-  public commonAnim: CommonAnim;
+  public commonAnim: CommonAnim | null;
 
-  constructor(commonAnim: CommonAnim, user: Pokemon, target?: Pokemon) {
+  constructor(commonAnim: CommonAnim | null, user: Pokemon, target?: Pokemon) {
     super(user, target || user);
 
     this.commonAnim = commonAnim;
   }
 
-  getAnim(): AnimConfig {
-    return commonAnims.get(this.commonAnim);
+  getAnim(): AnimConfig | null {
+    return this.commonAnim ? commonAnims.get(this.commonAnim)! : null; // TODO: is this bang correct?
   }
 
   isOppAnim(): boolean {
@@ -1009,11 +1010,11 @@ export class MoveAnim extends BattleAnim {
   getAnim(): AnimConfig {
     return moveAnims.get(this.move) instanceof AnimConfig
       ? moveAnims.get(this.move) as AnimConfig
-      : moveAnims.get(this.move)[this.user.isPlayer() ? 0 : 1] as AnimConfig;
+      : moveAnims.get(this.move)![this.user?.isPlayer() ? 0 : 1] as AnimConfig; // TODO: is this bang correct?
   }
 
   isOppAnim(): boolean {
-    return !this.user.isPlayer() && Array.isArray(moveAnims.get(this.move));
+    return !this.user?.isPlayer() && Array.isArray(moveAnims.get(this.move));
   }
 
   protected isHideUser(): boolean {
@@ -1035,13 +1036,13 @@ export class MoveChargeAnim extends MoveAnim {
   }
 
   isOppAnim(): boolean {
-    return !this.user.isPlayer() && Array.isArray(chargeAnims.get(this.chargeAnim));
+    return !this.user?.isPlayer() && Array.isArray(chargeAnims.get(this.chargeAnim));
   }
 
   getAnim(): AnimConfig {
     return chargeAnims.get(this.chargeAnim) instanceof AnimConfig
       ? chargeAnims.get(this.chargeAnim) as AnimConfig
-      : chargeAnims.get(this.chargeAnim)[this.user.isPlayer() ? 0 : 1] as AnimConfig;
+      : chargeAnims.get(this.chargeAnim)![this.user?.isPlayer() ? 0 : 1] as AnimConfig; // TODO: is this bang correct?
   }
 }
 
@@ -1059,19 +1060,19 @@ export async function populateAnims() {
     moveNameToId[moveName] = move;
   }
 
-  const seNames = [];//(await fs.readdir('./public/audio/se/battle_anims/')).map(se => se.toString());
+  const seNames: string[] = [];//(await fs.readdir('./public/audio/se/battle_anims/')).map(se => se.toString());
 
-  const animsData = [];//battleAnimRawData.split('!ruby/array:PBAnimation').slice(1);
+  const animsData : any[] = [];//battleAnimRawData.split('!ruby/array:PBAnimation').slice(1); // TODO: add a proper type
   for (let a = 0; a < animsData.length; a++) {
     const fields = animsData[a].split("@").slice(1);
 
     const nameField = fields.find(f => f.startsWith("name: "));
 
-    let isOppMove: boolean;
-    let commonAnimId: CommonAnim;
-    let chargeAnimId: ChargeAnim;
+    let isOppMove: boolean | undefined;
+    let commonAnimId: CommonAnim | undefined;
+    let chargeAnimId: ChargeAnim | undefined;
     if (!nameField.startsWith("name: Move:") && !(isOppMove = nameField.startsWith("name: OppMove:"))) {
-      const nameMatch = commonNamePattern.exec(nameField);
+      const nameMatch = commonNamePattern.exec(nameField)!; // TODO: is this bang correct?
       const name = nameMatch[2].toLowerCase();
       if (commonAnimMatchNames.indexOf(name) > -1) {
         commonAnimId = commonAnimIds[commonAnimMatchNames.indexOf(name)];
@@ -1128,14 +1129,14 @@ export async function populateAnims() {
         for (let t = 0; t < timingEntries.length; t++) {
           const timingData = timingEntries[t].replace(/\n/g, " ").replace(/[ ]{2,}/g, " ").replace(/[a-z]+: ! '', /ig, "").replace(/name: (.*?),/, "name: \"$1\",")
             .replace(/flashColor: !ruby\/object:Color { alpha: ([\d\.]+), blue: ([\d\.]+), green: ([\d\.]+), red: ([\d\.]+)}/, "flashRed: $4, flashGreen: $3, flashBlue: $2, flashAlpha: $1");
-          const frameIndex = parseInt(/frame: (\d+)/.exec(timingData)[1]);
-          let resourceName = /name: "(.*?)"/.exec(timingData)[1].replace("''", "");
-          const timingType = parseInt(/timingType: (\d)/.exec(timingData)[1]);
-          let timedEvent: AnimTimedEvent;
+          const frameIndex = parseInt(/frame: (\d+)/.exec(timingData)![1]); // TODO: is the bang correct?
+          let resourceName = /name: "(.*?)"/.exec(timingData)![1].replace("''", ""); // TODO: is the bang correct?
+          const timingType = parseInt(/timingType: (\d)/.exec(timingData)![1]); // TODO: is the bang correct?
+          let timedEvent: AnimTimedEvent | undefined;
           switch (timingType) {
           case 0:
             if (resourceName && resourceName.indexOf(".") === -1) {
-              let ext: string;
+              let ext: string | undefined;
               [ "wav", "mp3", "m4a" ].every(e => {
                 if (seNames.indexOf(`${resourceName}.${e}`) > -1) {
                   ext = e;
@@ -1162,7 +1163,7 @@ export async function populateAnims() {
           }
           const propPattern = /([a-z]+): (.*?)(?:,|\})/ig;
           let propMatch: RegExpExecArray;
-          while ((propMatch = propPattern.exec(timingData))) {
+          while ((propMatch = propPattern.exec(timingData)!)) { // TODO: is this bang correct?
             const prop = propMatch[1];
             let value: any = propMatch[2];
             switch (prop) {
@@ -1194,7 +1195,7 @@ export async function populateAnims() {
           if (!anim.frameTimedEvents.has(frameIndex)) {
             anim.frameTimedEvents.set(frameIndex, []);
           }
-          anim.frameTimedEvents.get(frameIndex).push(timedEvent);
+          anim.frameTimedEvents.get(frameIndex)!.push(timedEvent); // TODO: is this bang correct?
         }
         break;
       case "position":
diff --git a/src/data/battler-tags.ts b/src/data/battler-tags.ts
index dd5ab8938ae..c25407d0599 100644
--- a/src/data/battler-tags.ts
+++ b/src/data/battler-tags.ts
@@ -36,11 +36,11 @@ export class BattlerTag {
   public sourceMove: Moves;
   public sourceId?: number;
 
-  constructor(tagType: BattlerTagType, lapseType: BattlerTagLapseType | BattlerTagLapseType[], turnCount: number, sourceMove: Moves, sourceId?: number) {
+  constructor(tagType: BattlerTagType, lapseType: BattlerTagLapseType | BattlerTagLapseType[], turnCount: number, sourceMove?: Moves, sourceId?: number) {
     this.tagType = tagType;
     this.lapseTypes = Array.isArray(lapseType) ? lapseType : [ lapseType ];
     this.turnCount = turnCount;
-    this.sourceMove = sourceMove;
+    this.sourceMove = sourceMove!; // TODO: is this bang correct?
     this.sourceId = sourceId;
   }
 
@@ -66,7 +66,7 @@ export class BattlerTag {
     return false;
   }
 
-  getMoveName(): string {
+  getMoveName(): string | null {
     return this.sourceMove
       ? allMoves[this.sourceMove].name
       : null;
@@ -299,12 +299,12 @@ export class DestinyBondTag extends BattlerTag {
     if (lapseType !== BattlerTagLapseType.CUSTOM) {
       return super.lapse(pokemon, lapseType);
     }
-    const source = pokemon.scene.getPokemonById(this.sourceId);
-    if (!source.isFainted()) {
+    const source = this.sourceId ? pokemon.scene.getPokemonById(this.sourceId) : null;
+    if (!source?.isFainted()) {
       return true;
     }
 
-    if (source.getAlly() === pokemon) {
+    if (source?.getAlly() === pokemon) {
       return false;
     }
 
@@ -330,7 +330,19 @@ export class InfatuatedTag extends BattlerTag {
   }
 
   canAdd(pokemon: Pokemon): boolean {
-    return pokemon.isOppositeGender(pokemon.scene.getPokemonById(this.sourceId));
+    if (this.sourceId) {
+      const pkm = pokemon.scene.getPokemonById(this.sourceId);
+
+      if (pkm) {
+        return pokemon.isOppositeGender(pkm);
+      } else  {
+        console.warn("canAdd: this.sourceId is not a valid pokemon id!", this.sourceId);
+        return false;
+      }
+    } else {
+      console.warn("canAdd: this.sourceId is undefined");
+      return false;
+    }
   }
 
   onAdd(pokemon: Pokemon): void {
@@ -339,7 +351,7 @@ export class InfatuatedTag extends BattlerTag {
     pokemon.scene.queueMessage(
       i18next.t("battle:battlerTagsInfatuatedOnAdd", {
         pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-        sourcePokemonName: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId))
+        sourcePokemonName: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId!) ?? undefined) // TODO: is that bang correct?
       })
     );
   }
@@ -357,7 +369,7 @@ export class InfatuatedTag extends BattlerTag {
       pokemon.scene.queueMessage(
         i18next.t("battle:battlerTagsInfatuatedLapse", {
           pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-          sourcePokemonName: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId))
+          sourcePokemonName: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId!) ?? undefined) // TODO: is that bang correct?
         })
       );
       pokemon.scene.unshiftPhase(new CommonAnimPhase(pokemon.scene, pokemon.getBattlerIndex(), undefined, CommonAnim.ATTRACT));
@@ -410,7 +422,7 @@ export class SeedTag extends BattlerTag {
     super.onAdd(pokemon);
 
     pokemon.scene.queueMessage(i18next.t("battle:battlerTagsSeededOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(pokemon) }));
-    this.sourceIndex = pokemon.scene.getPokemonById(this.sourceId).getBattlerIndex();
+    this.sourceIndex = pokemon.scene.getPokemonById(this.sourceId!)!.getBattlerIndex(); // TODO: are those bangs correct?
   }
 
   lapse(pokemon: Pokemon, lapseType: BattlerTagLapseType): boolean {
@@ -556,11 +568,11 @@ export class EncoreTag extends BattlerTag {
 
     const movePhase = pokemon.scene.findPhase(m => m instanceof MovePhase && m.pokemon === pokemon);
     if (movePhase) {
-      const movesetMove = pokemon.getMoveset().find(m => m.moveId === this.moveId);
+      const movesetMove = pokemon.getMoveset().find(m => m!.moveId === this.moveId); // TODO: is this bang correct?
       if (movesetMove) {
         const lastMove = pokemon.getLastXMoves(1)[0];
         pokemon.scene.tryReplacePhase((m => m instanceof MovePhase && m.pokemon === pokemon),
-          new MovePhase(pokemon.scene, pokemon, lastMove.targets, movesetMove));
+          new MovePhase(pokemon.scene, pokemon, lastMove.targets!, movesetMove)); // TODO: is this bang correct?
       }
     }
   }
@@ -580,7 +592,7 @@ export class HelpingHandTag extends BattlerTag {
   onAdd(pokemon: Pokemon): void {
     pokemon.scene.queueMessage(
       i18next.t("battle:battlerTagsHelpingHandOnAdd", {
-        pokemonNameWithAffix: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId)),
+        pokemonNameWithAffix: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
         pokemonName: getPokemonNameWithAffix(pokemon)
       })
     );
@@ -800,7 +812,7 @@ export class BindTag extends DamagingTrapTag {
   getTrapMessage(pokemon: Pokemon): string {
     return i18next.t("battle:battlerTagsBindOnTrap", {
       pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-      sourcePokemonName: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId)),
+      sourcePokemonName: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
       moveName: this.getMoveName()
     });
   }
@@ -814,7 +826,7 @@ export class WrapTag extends DamagingTrapTag {
   getTrapMessage(pokemon: Pokemon): string {
     return i18next.t("battle:battlerTagsWrapOnTrap", {
       pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-      sourcePokemonName: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId))
+      sourcePokemonName: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
     });
   }
 }
@@ -848,7 +860,7 @@ export class ClampTag extends DamagingTrapTag {
 
   getTrapMessage(pokemon: Pokemon): string {
     return i18next.t("battle:battlerTagsClampOnTrap", {
-      sourcePokemonNameWithAffix: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId)),
+      sourcePokemonNameWithAffix: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
       pokemonName: getPokemonNameWithAffix(pokemon),
     });
   }
@@ -895,7 +907,7 @@ export class ThunderCageTag extends DamagingTrapTag {
   getTrapMessage(pokemon: Pokemon): string {
     return i18next.t("battle:battlerTagsThunderCageOnTrap", {
       pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-      sourcePokemonNameWithAffix: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId))
+      sourcePokemonNameWithAffix: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
     });
   }
 }
@@ -908,7 +920,7 @@ export class InfestationTag extends DamagingTrapTag {
   getTrapMessage(pokemon: Pokemon): string {
     return i18next.t("battle:battlerTagsInfestationOnTrap", {
       pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-      sourcePokemonNameWithAffix: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId))
+      sourcePokemonNameWithAffix: getPokemonNameWithAffix(pokemon.scene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
     });
   }
 }
@@ -1242,6 +1254,7 @@ export class HighestStatBoostTag extends AbilityBattlerTag {
       return highestValue;
     }, 0);
 
+    highestStat = highestStat!; // tell TS compiler it's defined!
     this.stat = highestStat;
 
     switch (this.stat) {
@@ -1427,7 +1440,7 @@ export class SaltCuredTag extends BattlerTag {
     super.onAdd(pokemon);
 
     pokemon.scene.queueMessage(i18next.t("battle:battlerTagsSaltCuredOnAdd", { pokemonNameWithAffix: getPokemonNameWithAffix(pokemon) }));
-    this.sourceIndex = pokemon.scene.getPokemonById(this.sourceId).getBattlerIndex();
+    this.sourceIndex = pokemon.scene.getPokemonById(this.sourceId!)!.getBattlerIndex(); // TODO: are those bangs correct?
   }
 
   lapse(pokemon: Pokemon, lapseType: BattlerTagLapseType): boolean {
@@ -1474,7 +1487,7 @@ export class CursedTag extends BattlerTag {
 
   onAdd(pokemon: Pokemon): void {
     super.onAdd(pokemon);
-    this.sourceIndex = pokemon.scene.getPokemonById(this.sourceId).getBattlerIndex();
+    this.sourceIndex = pokemon.scene.getPokemonById(this.sourceId!)!.getBattlerIndex(); // TODO: are those bangs correct?
   }
 
   lapse(pokemon: Pokemon, lapseType: BattlerTagLapseType): boolean {
diff --git a/src/data/berry.ts b/src/data/berry.ts
index 5ca64544544..30b89848452 100644
--- a/src/data/berry.ts
+++ b/src/data/berry.ts
@@ -54,7 +54,7 @@ export function getBerryPredicate(berryType: BerryType): BerryPredicate {
     return (pokemon: Pokemon) => {
       const threshold = new Utils.NumberHolder(0.25);
       applyAbAttrs(ReduceBerryUseThresholdAbAttr, pokemon, null, threshold);
-      return !!pokemon.getMoveset().find(m => !m.getPpRatio());
+      return !!pokemon.getMoveset().find(m => !m?.getPpRatio());
     };
   }
 }
@@ -120,10 +120,10 @@ export function getBerryEffectFunc(berryType: BerryType): BerryEffectFunc {
       if (pokemon.battleData) {
         pokemon.battleData.berriesEaten.push(berryType);
       }
-      const ppRestoreMove = pokemon.getMoveset().find(m => !m.getPpRatio()) ? pokemon.getMoveset().find(m => !m.getPpRatio()) : pokemon.getMoveset().find(m => m.getPpRatio() < 1);
+      const ppRestoreMove = pokemon.getMoveset().find(m => !m?.getPpRatio()) ? pokemon.getMoveset().find(m => !m?.getPpRatio()) : pokemon.getMoveset().find(m => m!.getPpRatio() < 1); // TODO: is this bang correct?
       if (ppRestoreMove !== undefined) {
-        ppRestoreMove.ppUsed = Math.max(ppRestoreMove.ppUsed - 10, 0);
-        pokemon.scene.queueMessage(i18next.t("battle:ppHealBerry", { pokemonNameWithAffix: getPokemonNameWithAffix(pokemon), moveName: ppRestoreMove.getName(), berryName: getBerryName(berryType) }));
+        ppRestoreMove!.ppUsed = Math.max(ppRestoreMove!.ppUsed - 10, 0);
+        pokemon.scene.queueMessage(i18next.t("battle:ppHealBerry", { pokemonNameWithAffix: getPokemonNameWithAffix(pokemon), moveName: ppRestoreMove!.getName(), berryName: getBerryName(berryType) }));
       }
     };
   }
diff --git a/src/data/biomes.ts b/src/data/biomes.ts
index 479e0994cb6..ed579112249 100644
--- a/src/data/biomes.ts
+++ b/src/data/biomes.ts
@@ -7705,7 +7705,7 @@ export function initBiomes() {
       ? pokemonEvolutions[speciesId]
       : [];
 
-    if (!biomeEntries.filter(b => b[0] !== Biome.END).length && !speciesEvolutions.filter(es => !!((pokemonBiomes.find(p => p[0] === es.speciesId))[3] as any[]).filter(b => b[0] !== Biome.END).length).length) {
+    if (!biomeEntries.filter(b => b[0] !== Biome.END).length && !speciesEvolutions.filter(es => !!((pokemonBiomes.find(p => p[0] === es.speciesId)!)[3] as any[]).filter(b => b[0] !== Biome.END).length).length) { // TODO: is the bang on the `find()` correct?
       uncatchableSpecies.push(speciesId);
     }
 
diff --git a/src/data/challenge.ts b/src/data/challenge.ts
index 7bea68e36c7..5f17fdedb78 100644
--- a/src/data/challenge.ts
+++ b/src/data/challenge.ts
@@ -412,7 +412,7 @@ export class SingleGenerationChallenge extends Challenge {
       const speciesToCheck = [pokemon.speciesId];
       while (speciesToCheck.length) {
         const checking = speciesToCheck.pop();
-        if (pokemonEvolutions.hasOwnProperty(checking) && checkPokemonEvolutions) {
+        if (checking && pokemonEvolutions.hasOwnProperty(checking) && checkPokemonEvolutions) {
           pokemonEvolutions[checking].forEach(e => {
             speciesToCheck.push(e.speciesId);
             generations.push(getPokemonSpecies(e.speciesId).generation);
@@ -430,7 +430,7 @@ export class SingleGenerationChallenge extends Challenge {
 
   applyPokemonInBattle(pokemon: Pokemon, valid: Utils.BooleanHolder): boolean {
     const baseGeneration = pokemon.species.speciesId === Species.VICTINI ? 5 : getPokemonSpecies(pokemon.species.speciesId).generation;
-    const fusionGeneration = pokemon.isFusion() ? pokemon.fusionSpecies.speciesId === Species.VICTINI ? 5 : getPokemonSpecies(pokemon.fusionSpecies.speciesId).generation : 0;
+    const fusionGeneration = pokemon.isFusion() ? pokemon.fusionSpecies?.speciesId === Species.VICTINI ? 5 : getPokemonSpecies(pokemon.fusionSpecies!.speciesId).generation : 0; // TODO: is the bang on fusionSpecies correct?
     if (pokemon.isPlayer() && (baseGeneration !== this.value || (pokemon.isFusion() && fusionGeneration !== this.value))) {
       valid.value = false;
       return true;
@@ -542,13 +542,13 @@ export class SingleTypeChallenge extends Challenge {
       const speciesToCheck = [pokemon.speciesId];
       while (speciesToCheck.length) {
         const checking = speciesToCheck.pop();
-        if (pokemonEvolutions.hasOwnProperty(checking) && checkPokemonEvolutions) {
+        if (checking && pokemonEvolutions.hasOwnProperty(checking) && checkPokemonEvolutions) {
           pokemonEvolutions[checking].forEach(e => {
             speciesToCheck.push(e.speciesId);
             types.push(getPokemonSpecies(e.speciesId).type1, getPokemonSpecies(e.speciesId).type2);
           });
         }
-        if (pokemonFormChanges.hasOwnProperty(checking) && checkPokemonForms) {
+        if (checking && pokemonFormChanges.hasOwnProperty(checking) && checkPokemonForms) {
           pokemonFormChanges[checking].forEach(f1 => {
             getPokemonSpecies(checking).forms.forEach(f2 => {
               if (f1.formKey === f2.formKey) {
@@ -568,10 +568,11 @@ export class SingleTypeChallenge extends Challenge {
 
   applyPokemonInBattle(pokemon: Pokemon, valid: Utils.BooleanHolder): boolean {
     if (pokemon.isPlayer() && !pokemon.isOfType(this.value - 1, false, false, true)
-      && !SingleTypeChallenge.TYPE_OVERRIDES.some(o => o.type === (this.value - 1) && (pokemon.isFusion() && o.fusion ? pokemon.fusionSpecies : pokemon.species).speciesId === o.species)) {
+      && !SingleTypeChallenge.TYPE_OVERRIDES.some(o => o.type === (this.value - 1) && (pokemon.isFusion() && o.fusion ? pokemon.fusionSpecies! : pokemon.species).speciesId === o.species)) { // TODO: is the bang on fusionSpecies correct?
       valid.value = false;
       return true;
     }
+    return false;
   }
 
   /**
diff --git a/src/data/daily-run.ts b/src/data/daily-run.ts
index 4b741b6f473..b7e03b4b189 100644
--- a/src/data/daily-run.ts
+++ b/src/data/daily-run.ts
@@ -11,15 +11,15 @@ export interface DailyRunConfig {
   starters: Starter;
 }
 
-export function fetchDailyRunSeed(): Promise<string> {
-  return new Promise<string>((resolve, reject) => {
+export function fetchDailyRunSeed(): Promise<string | null> {
+  return new Promise<string | null>((resolve, reject) => {
     Utils.apiFetch("daily/seed").then(response => {
       if (!response.ok) {
         resolve(null);
         return;
       }
       return response.text();
-    }).then(seed => resolve(seed))
+    }).then(seed => resolve(seed!)) // TODO: is this bang correct?
       .catch(err => reject(err));
   });
 }
diff --git a/src/data/egg.ts b/src/data/egg.ts
index cb889951488..9c76591f01b 100644
--- a/src/data/egg.ts
+++ b/src/data/egg.ts
@@ -140,30 +140,30 @@ export class Egg {
   constructor(eggOptions?: IEggOptions) {
     //if (eggOptions.tier && eggOptions.species) throw Error("Error egg can't have species and tier as option. only choose one of them.")
 
-    this._sourceType = eggOptions.sourceType ?? undefined;
+    this._sourceType = eggOptions?.sourceType!; // TODO: is this bang correct?
     // Ensure _sourceType is defined before invoking rollEggTier(), as it is referenced
-    this._tier = eggOptions.tier ?? (Overrides.EGG_TIER_OVERRIDE ?? this.rollEggTier());
+    this._tier = eggOptions?.tier ?? (Overrides.EGG_TIER_OVERRIDE ?? this.rollEggTier());
     // If egg was pulled, check if egg pity needs to override the egg tier
-    if (eggOptions.pulled) {
+    if (eggOptions?.pulled) {
       // Needs this._tier and this._sourceType to work
-      this.checkForPityTierOverrides(eggOptions.scene);
+      this.checkForPityTierOverrides(eggOptions.scene!); // TODO: is this bang correct?
     }
 
-    this._id = eggOptions.id ?? Utils.randInt(EGG_SEED, EGG_SEED * this._tier);
+    this._id = eggOptions?.id ?? Utils.randInt(EGG_SEED, EGG_SEED * this._tier);
 
-    this._sourceType = eggOptions.sourceType ?? undefined;
-    this._hatchWaves = eggOptions.hatchWaves ?? this.getEggTierDefaultHatchWaves();
-    this._timestamp = eggOptions.timestamp ?? new Date().getTime();
+    this._sourceType = eggOptions?.sourceType ?? undefined;
+    this._hatchWaves = eggOptions?.hatchWaves ?? this.getEggTierDefaultHatchWaves();
+    this._timestamp = eggOptions?.timestamp ?? new Date().getTime();
 
     // First roll shiny and variant so we can filter if species with an variant exist
-    this._isShiny = eggOptions.isShiny ?? (Overrides.EGG_SHINY_OVERRIDE || this.rollShiny());
-    this._variantTier = eggOptions.variantTier ?? (Overrides.EGG_VARIANT_OVERRIDE ?? this.rollVariant());
-    this._species = eggOptions.species ?? this.rollSpecies(eggOptions.scene);
+    this._isShiny = eggOptions?.isShiny ?? (Overrides.EGG_SHINY_OVERRIDE || this.rollShiny());
+    this._variantTier = eggOptions?.variantTier ?? (Overrides.EGG_VARIANT_OVERRIDE ?? this.rollVariant());
+    this._species = eggOptions?.species ?? this.rollSpecies(eggOptions!.scene!)!; // TODO: Are those bangs correct?
 
-    this._overrideHiddenAbility = eggOptions.overrideHiddenAbility ?? false;
+    this._overrideHiddenAbility = eggOptions?.overrideHiddenAbility ?? false;
 
     // Override egg tier and hatchwaves if species was given
-    if (eggOptions.species) {
+    if (eggOptions?.species) {
       this._tier = this.getEggTierFromSpeciesStarterValue();
       this._hatchWaves = eggOptions.hatchWaves ?? this.getEggTierDefaultHatchWaves();
     }
@@ -174,10 +174,10 @@ export class Egg {
       this._variantTier = VariantTier.COMMON;
     }
     // Needs this._tier so it needs to be generated afer the tier override if bought from same species
-    this._eggMoveIndex = eggOptions.eggMoveIndex ?? this.rollEggMoveIndex();
-    if (eggOptions.pulled) {
-      this.increasePullStatistic(eggOptions.scene);
-      this.addEggToGameData(eggOptions.scene);
+    this._eggMoveIndex = eggOptions?.eggMoveIndex ?? this.rollEggMoveIndex();
+    if (eggOptions?.pulled) {
+      this.increasePullStatistic(eggOptions.scene!); // TODO: is this bang correct?
+      this.addEggToGameData(eggOptions.scene!); // TODO: is this bang correct?
     }
   }
 
@@ -202,7 +202,7 @@ export class Egg {
     // Legacy egg wants to hatch. Generate missing properties
     if (!this._species) {
       this._isShiny = this.rollShiny();
-      this._species = this.rollSpecies(scene);
+      this._species = this.rollSpecies(scene!)!; // TODO: are these bangs correct?
     }
 
     let pokemonSpecies = getPokemonSpecies(this._species);
@@ -213,7 +213,7 @@ export class Egg {
 
     // Sets the hidden ability if a hidden ability exists and the override is set
     // or if the same species egg hits the chance
-    let abilityIndex = undefined;
+    let abilityIndex: number | undefined = undefined;
     if (pokemonSpecies.abilityHidden && (this._overrideHiddenAbility
       || (this._sourceType === EggSourceType.SAME_SPECIES_EGG && !Utils.randSeedInt(SAME_SPECIES_EGG_HA_RATE)))) {
       abilityIndex = 2;
@@ -277,6 +277,9 @@ export class Egg {
       return i18next.t("egg:gachaTypeShiny");
     case EggSourceType.GACHA_MOVE:
       return i18next.t("egg:gachaTypeMove");
+    default:
+      console.warn("getEggTypeDescriptor case not defined. Returning default empty string");
+      return "";
     }
   }
 
@@ -326,9 +329,9 @@ export class Egg {
     return tierValue >= 52 + tierValueOffset ? EggTier.COMMON : tierValue >= 8 + tierValueOffset ? EggTier.GREAT : tierValue >= 1 + tierValueOffset ? EggTier.ULTRA : EggTier.MASTER;
   }
 
-  private rollSpecies(scene: BattleScene): Species {
+  private rollSpecies(scene: BattleScene): Species | null {
     if (!scene) {
-      return undefined;
+      return null;
     }
     /**
      * Manaphy eggs have a 1/8 chance of being Manaphy and 7/8 chance of being Phione
@@ -400,7 +403,7 @@ export class Egg {
      * and being the same each time
      */
     let totalWeight = 0;
-    const speciesWeights = [];
+    const speciesWeights : number[] = [];
     for (const speciesId of speciesPool) {
       let weight = Math.floor((((maxStarterValue - speciesStarters[speciesId]) / ((maxStarterValue - minStarterValue) + 1)) * 1.5 + 1) * 100);
       const species = getPokemonSpecies(speciesId);
@@ -420,6 +423,7 @@ export class Egg {
         break;
       }
     }
+    species = species!; // tell TS compiled it's defined now!
 
     if (!!scene.gameData.dexData[species].caughtAttr || scene.gameData.eggs.some(e => e.species === species)) {
       scene.gameData.unlockPity[this.tier] = Math.min(scene.gameData.unlockPity[this.tier] + 1, 10);
@@ -517,6 +521,8 @@ export class Egg {
     if (speciesStartValue >= 8) {
       return EggTier.MASTER;
     }
+
+    return EggTier.COMMON;
   }
 
   ////
@@ -541,6 +547,7 @@ export function getLegendaryGachaSpeciesForTimestamp(scene: BattleScene, timesta
   scene.executeWithSeedOffset(() => {
     ret = Phaser.Math.RND.shuffle(legendarySpecies)[index];
   }, offset, EGG_SEED.toString());
+  ret = ret!; // tell TS compiler it's
 
   return ret;
 }
diff --git a/src/data/move.ts b/src/data/move.ts
index 589c169805d..b5ca217a73e 100644
--- a/src/data/move.ts
+++ b/src/data/move.ts
@@ -180,7 +180,7 @@ export default class Move implements Localizable {
    * @returns the first {@linkcode MoveAttr} element in attrs that makes the input function return true
    */
   findAttr(attrPredicate: (attr: MoveAttr) => boolean): MoveAttr {
-    return this.attrs.find(attrPredicate);
+    return this.attrs.find(attrPredicate)!; // TODO: is the bang correct?
   }
 
   /**
@@ -361,7 +361,7 @@ export default class Move implements Localizable {
    * @param makesContact The value (boolean) to set the flag to
    * @returns The {@linkcode Move} that called this function
    */
-  makesContact(makesContact?: boolean): this {
+  makesContact(makesContact: boolean = true): this { // TODO: is true the correct default?
     this.setFlag(MoveFlags.MAKES_CONTACT, makesContact);
     return this;
   }
@@ -372,7 +372,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.CURSE}
    * @returns The {@linkcode Move} that called this function
    */
-  ignoresProtect(ignoresProtect?: boolean): this {
+  ignoresProtect(ignoresProtect: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.IGNORE_PROTECT, ignoresProtect);
     return this;
   }
@@ -383,7 +383,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.NATURE_POWER}
    * @returns The {@linkcode Move} that called this function
    */
-  ignoresVirtual(ignoresVirtual?: boolean): this {
+  ignoresVirtual(ignoresVirtual: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.IGNORE_VIRTUAL, ignoresVirtual);
     return this;
   }
@@ -394,7 +394,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.UPROAR}
    * @returns The {@linkcode Move} that called this function
    */
-  soundBased(soundBased?: boolean): this {
+  soundBased(soundBased: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.SOUND_BASED, soundBased);
     return this;
   }
@@ -405,7 +405,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.TELEPORT}
    * @returns The {@linkcode Move} that called this function
    */
-  hidesUser(hidesUser?: boolean): this {
+  hidesUser(hidesUser: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.HIDE_USER, hidesUser);
     return this;
   }
@@ -416,7 +416,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.WHIRLWIND}
    * @returns The {@linkcode Move} that called this function
    */
-  hidesTarget(hidesTarget?: boolean): this {
+  hidesTarget(hidesTarget: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.HIDE_TARGET, hidesTarget);
     return this;
   }
@@ -427,7 +427,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.BITE}
    * @returns The {@linkcode Move} that called this function
    */
-  bitingMove(bitingMove?: boolean): this {
+  bitingMove(bitingMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.BITING_MOVE, bitingMove);
     return this;
   }
@@ -438,7 +438,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.WATER_PULSE}
    * @returns The {@linkcode Move} that called this function
    */
-  pulseMove(pulseMove?: boolean): this {
+  pulseMove(pulseMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.PULSE_MOVE, pulseMove);
     return this;
   }
@@ -449,7 +449,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.DRAIN_PUNCH}
    * @returns The {@linkcode Move} that called this function
    */
-  punchingMove(punchingMove?: boolean): this {
+  punchingMove(punchingMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.PUNCHING_MOVE, punchingMove);
     return this;
   }
@@ -460,7 +460,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.X_SCISSOR}
    * @returns The {@linkcode Move} that called this function
    */
-  slicingMove(slicingMove?: boolean): this {
+  slicingMove(slicingMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.SLICING_MOVE, slicingMove);
     return this;
   }
@@ -471,7 +471,7 @@ export default class Move implements Localizable {
    * @param recklessMove The value to set the flag to
    * @returns The {@linkcode Move} that called this function
    */
-  recklessMove(recklessMove?: boolean): this {
+  recklessMove(recklessMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.RECKLESS_MOVE, recklessMove);
     return this;
   }
@@ -482,7 +482,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.ELECTRO_BALL}
    * @returns The {@linkcode Move} that called this function
    */
-  ballBombMove(ballBombMove?: boolean): this {
+  ballBombMove(ballBombMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.BALLBOMB_MOVE, ballBombMove);
     return this;
   }
@@ -493,7 +493,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.STUN_SPORE}
    * @returns The {@linkcode Move} that called this function
    */
-  powderMove(powderMove?: boolean): this {
+  powderMove(powderMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.POWDER_MOVE, powderMove);
     return this;
   }
@@ -504,7 +504,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.PETAL_DANCE}
    * @returns The {@linkcode Move} that called this function
    */
-  danceMove(danceMove?: boolean): this {
+  danceMove(danceMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.DANCE_MOVE, danceMove);
     return this;
   }
@@ -515,7 +515,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.HURRICANE}
    * @returns The {@linkcode Move} that called this function
    */
-  windMove(windMove?: boolean): this {
+  windMove(windMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.WIND_MOVE, windMove);
     return this;
   }
@@ -526,7 +526,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.ABSORB}
    * @returns The {@linkcode Move} that called this function
    */
-  triageMove(triageMove?: boolean): this {
+  triageMove(triageMove: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.TRIAGE_MOVE, triageMove);
     return this;
   }
@@ -537,7 +537,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.SUNSTEEL_STRIKE}
    * @returns The {@linkcode Move} that called this function
    */
-  ignoresAbilities(ignoresAbilities?: boolean): this {
+  ignoresAbilities(ignoresAbilities: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.IGNORE_ABILITIES, ignoresAbilities);
     return this;
   }
@@ -548,7 +548,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.TRIPLE_AXEL}
    * @returns The {@linkcode Move} that called this function
    */
-  checkAllHits(checkAllHits?: boolean): this {
+  checkAllHits(checkAllHits: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.CHECK_ALL_HITS, checkAllHits);
     return this;
   }
@@ -559,7 +559,7 @@ export default class Move implements Localizable {
    * example: @see {@linkcode Moves.METAL_BURST}
    * @returns The {@linkcode Move} that called this function
    */
-  redirectCounter(redirectCounter?: boolean): this {
+  redirectCounter(redirectCounter: boolean = true): this { // TODO: is `true` the correct default?
     this.setFlag(MoveFlags.REDIRECT_COUNTER, redirectCounter);
     return this;
   }
@@ -571,7 +571,7 @@ export default class Move implements Localizable {
    * @param target {@linkcode Pokemon} the Pokemon receiving the move
    * @returns boolean
    */
-  checkFlag(flag: MoveFlags, user: Pokemon, target: Pokemon): boolean {
+  checkFlag(flag: MoveFlags, user: Pokemon, target: Pokemon | null): boolean {
     // special cases below, eg: if the move flag is MAKES_CONTACT, and the user pokemon has an ability that ignores contact (like "Long Reach"), then overrides and move does not make contact
     switch (flag) {
     case MoveFlags.MAKES_CONTACT:
@@ -870,7 +870,7 @@ export abstract class MoveAttr {
    * @param args Set of unique arguments needed by this attribute
    * @returns true if application of the ability succeeds
    */
-  apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean | Promise<boolean> {
+  apply(user: Pokemon | null, target: Pokemon | null, move: Move, args: any[]): boolean | Promise<boolean> {
     return true;
   }
 
@@ -878,7 +878,7 @@ export abstract class MoveAttr {
    * @virtual
    * @returns the {@linkcode MoveCondition} or {@linkcode MoveConditionFunc} for this {@linkcode Move}
    */
-  getCondition(): MoveCondition | MoveConditionFunc {
+  getCondition(): MoveCondition | MoveConditionFunc | null {
     return null;
   }
 
@@ -954,14 +954,14 @@ export class MoveEffectAttr extends MoveAttr {
    * @param args Set of unique arguments needed by this attribute
    * @returns true if basic application of the ability attribute should be possible
    */
-  canApply(user: Pokemon, target: Pokemon, move: Move, args: any[]) {
+  canApply(user: Pokemon, target: Pokemon, move: Move, args?: any[]) {
     return !! (this.selfTarget ? user.hp && !user.getTag(BattlerTagType.FRENZY) : target.hp)
            && (this.selfTarget || !target.getTag(BattlerTagType.PROTECTED) ||
                 move.checkFlag(MoveFlags.IGNORE_PROTECT, user, target));
   }
 
   /** Applies move effects so long as they are able based on {@linkcode canApply} */
-  apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean | Promise<boolean> {
+  apply(user: Pokemon, target: Pokemon, move: Move, args?: any[]): boolean | Promise<boolean> {
     return this.canApply(user, target, move, args);
   }
 
@@ -1408,10 +1408,10 @@ export class PartyStatusCureAttr extends MoveEffectAttr {
   /** Skips mons with this ability, ie. Soundproof */
   private abilityCondition: Abilities;
 
-  constructor(message: string, abilityCondition: Abilities) {
+  constructor(message: string | null, abilityCondition: Abilities) {
     super();
 
-    this.message = message;
+    this.message = message!; // TODO: is this bang correct?
     this.abilityCondition = abilityCondition;
   }
 
@@ -1428,6 +1428,7 @@ export class PartyStatusCureAttr extends MoveEffectAttr {
       return false;
     }
     this.addPartyCurePhase(user);
+    return true;
   }
 
   addPartyCurePhase(user: Pokemon) {
@@ -1583,16 +1584,16 @@ export class SandHealAttr extends WeatherHealAttr {
  */
 export class BoostHealAttr extends HealAttr {
   /** Healing received when {@linkcode condition} is false */
-  private normalHealRatio?: number;
+  private normalHealRatio: number;
   /** Healing received when {@linkcode condition} is true */
-  private boostedHealRatio?: number;
+  private boostedHealRatio: number;
   /** The lambda expression to check against when boosting the healing value */
   private condition?: MoveConditionFunc;
 
   constructor(normalHealRatio?: number, boostedHealRatio?: number, showAnim?: boolean, selfTarget?: boolean, condition?: MoveConditionFunc) {
     super(normalHealRatio, showAnim, selfTarget);
-    this.normalHealRatio = normalHealRatio;
-    this.boostedHealRatio = boostedHealRatio;
+    this.normalHealRatio = normalHealRatio!; // TODO: is this bang correct?
+    this.boostedHealRatio = boostedHealRatio!; // TODO: is this bang correct?
     this.condition = condition;
   }
 
@@ -1604,7 +1605,7 @@ export class BoostHealAttr extends HealAttr {
    * @returns true if the move was successful
    */
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
-    const healRatio = this.condition(user, target, move) ? this.boostedHealRatio : this.normalHealRatio;
+    const healRatio: number = (this.condition ? this.condition(user, target, move) : false) ? this.boostedHealRatio : this.normalHealRatio;
     this.addHealPhase(target, healRatio);
     return true;
   }
@@ -1643,13 +1644,13 @@ export class HealOnAllyAttr extends HealAttr {
 export class HitHealAttr extends MoveEffectAttr {
   private healRatio: number;
   private message: string;
-  private healStat: Stat;
+  private healStat: Stat | null;
 
-  constructor(healRatio?: number, healStat?: Stat) {
+  constructor(healRatio?: number | null, healStat?: Stat) {
     super(true, MoveEffectTrigger.HIT);
 
-    this.healRatio = healRatio || 0.5;
-    this.healStat = healStat || null;
+    this.healRatio = healRatio!; // TODO: is this bang correct?
+    this.healStat = healStat!; // TODO: is this bang correct?
   }
   /**
    * Heals the user the determined amount and possibly displays a message about regaining health.
@@ -1665,7 +1666,7 @@ export class HitHealAttr extends MoveEffectAttr {
     let healAmount = 0;
     let message = "";
     const reverseDrain = target.hasAbilityWithAttr(ReverseDrainAbAttr, false);
-    if (this.healStat) {
+    if (this.healStat !== null) {
       // Strength Sap formula
       healAmount = target.getBattleStat(this.healStat);
       message = i18next.t("battle:drainMessage", {pokemonName: getPokemonNameWithAffix(target)});
@@ -1677,11 +1678,11 @@ export class HitHealAttr extends MoveEffectAttr {
     if (reverseDrain) {
       if (user.hasAbilityWithAttr(BlockNonDirectDamageAbAttr)) {
         healAmount = 0;
-        message = null;
+        message = "";
       } else {
         user.turnData.damageTaken += healAmount;
         healAmount = healAmount * -1;
-        message = null;
+        message = "";
       }
     }
     user.scene.unshiftPhase(new PokemonHealPhase(user.scene, user.getBattlerIndex(), healAmount, message, false, true));
@@ -1850,14 +1851,14 @@ export class WaterShurikenMultiHitTypeAttr extends ChangeMultiHitTypeAttr {
 
 export class StatusEffectAttr extends MoveEffectAttr {
   public effect: StatusEffect;
-  public cureTurn: integer;
+  public cureTurn: integer | null;
   public overrideStatus: boolean;
 
   constructor(effect: StatusEffect, selfTarget?: boolean, cureTurn?: integer, overrideStatus?: boolean) {
     super(selfTarget, MoveEffectTrigger.HIT);
 
     this.effect = effect;
-    this.cureTurn = cureTurn;
+    this.cureTurn = cureTurn!; // TODO: is this bang correct?
     this.overrideStatus = !!overrideStatus;
   }
 
@@ -1875,7 +1876,7 @@ export class StatusEffectAttr extends MoveEffectAttr {
       }
       if ((!pokemon.status || (pokemon.status.effect === this.effect && moveChance < 0))
         && pokemon.trySetStatus(this.effect, true, user, this.cureTurn)) {
-        applyPostAttackAbAttrs(ConfusionOnStatusEffectAbAttr, user, target, move, null,this.effect);
+        applyPostAttackAbAttrs(ConfusionOnStatusEffectAbAttr, user, target, move, null, this.effect);
         return true;
       }
     }
@@ -1914,12 +1915,13 @@ export class PsychoShiftEffectAttr extends MoveEffectAttr {
   }
 
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
-    const statusToApply: StatusEffect = user.status?.effect ?? (user.hasAbility(Abilities.COMATOSE) ? StatusEffect.SLEEP : undefined);
+    const statusToApply: StatusEffect | undefined = user.status?.effect ?? (user.hasAbility(Abilities.COMATOSE) ? StatusEffect.SLEEP : undefined);
 
     if (target.status) {
       return false;
     }
-    if (!target.status || (target.status.effect === statusToApply && move.chance < 0)) {
+    //@ts-ignore - how can target.status.effect be checked when we return `false` before when it's defined?
+    if (!target.status || (target.status.effect === statusToApply && move.chance < 0)) { // TODO: resolve ts-ignore
       const statusAfflictResult = target.trySetStatus(statusToApply, true, user);
       if (statusAfflictResult) {
         if (user.status) {
@@ -1960,7 +1962,7 @@ export class StealHeldItemChanceAttr extends MoveEffectAttr {
       const heldItems = this.getTargetHeldItems(target).filter(i => i.isTransferrable);
       if (heldItems.length) {
         const poolType = target.isPlayer() ? ModifierPoolType.PLAYER : target.hasTrainer() ? ModifierPoolType.TRAINER : ModifierPoolType.WILD;
-        const highestItemTier = heldItems.map(m => m.type.getOrInferTier(poolType)).reduce((highestTier, tier) => Math.max(tier, highestTier), 0);
+        const highestItemTier = heldItems.map(m => m.type.getOrInferTier(poolType)).reduce((highestTier, tier) => Math.max(tier!, highestTier), 0); // TODO: is the bang after tier correct?
         const tierHeldItems = heldItems.filter(m => m.type.getOrInferTier(poolType) === highestItemTier);
         const stolenItem = tierHeldItems[user.randSeedInt(tierHeldItems.length)];
         user.scene.tryTransferHeldItemModifier(stolenItem, user, false).then(success => {
@@ -2073,10 +2075,9 @@ export class RemoveHeldItemAttr extends MoveEffectAttr {
  * Attribute that causes targets of the move to eat a berry. Used for Teatime, Stuff Cheeks
  */
 export class EatBerryAttr extends MoveEffectAttr {
-  protected chosenBerry: BerryModifier;
+  protected chosenBerry: BerryModifier | undefined;
   constructor() {
     super(true, MoveEffectTrigger.HIT);
-    this.chosenBerry = undefined;
   }
   /**
    * Causes the target to eat a berry.
@@ -2111,16 +2112,16 @@ export class EatBerryAttr extends MoveEffectAttr {
   }
 
   reduceBerryModifier(target: Pokemon) {
-    if (this.chosenBerry.stackCount === 1) {
+    if (this.chosenBerry?.stackCount === 1) {
       target.scene.removeModifier(this.chosenBerry, !target.isPlayer());
-    } else {
+    } else if (this.chosenBerry !== undefined && this.chosenBerry.stackCount > 1) {
       this.chosenBerry.stackCount--;
     }
     target.scene.updateModifiers(target.isPlayer());
   }
 
   eatBerry(consumer: Pokemon) {
-    getBerryEffectFunc(this.chosenBerry.berryType)(consumer); // consumer eats the berry
+    getBerryEffectFunc(this.chosenBerry!.berryType)(consumer); // consumer eats the berry
     applyAbAttrs(HealFromBerryUseAbAttr, consumer, new Utils.BooleanHolder(false));
   }
 }
@@ -2351,20 +2352,20 @@ export class OverrideMoveEffectAttr extends MoveAttr {
 export class ChargeAttr extends OverrideMoveEffectAttr {
   public chargeAnim: ChargeAnim;
   private chargeText: string;
-  private tagType: BattlerTagType;
+  private tagType: BattlerTagType | null;
   private chargeEffect: boolean;
   public sameTurn: boolean;
-  public followUpPriority: integer;
+  public followUpPriority: integer | null;
 
-  constructor(chargeAnim: ChargeAnim, chargeText: string, tagType?: BattlerTagType, chargeEffect: boolean = false, sameTurn: boolean = false, followUpPriority?: integer) {
+  constructor(chargeAnim: ChargeAnim, chargeText: string, tagType?: BattlerTagType | null, chargeEffect: boolean = false, sameTurn: boolean = false, followUpPriority?: integer) {
     super();
 
     this.chargeAnim = chargeAnim;
     this.chargeText = chargeText;
-    this.tagType = tagType;
+    this.tagType = tagType!; // TODO: is this bang correct?
     this.chargeEffect = chargeEffect;
     this.sameTurn = sameTurn;
-    this.followUpPriority = followUpPriority;
+    this.followUpPriority = followUpPriority!; // TODO: is this bang correct?
   }
 
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): Promise<boolean> {
@@ -2383,11 +2384,11 @@ export class ChargeAttr extends OverrideMoveEffectAttr {
           user.pushMoveHistory({ move: move.id, targets: [ target.getBattlerIndex() ], result: MoveResult.OTHER });
           user.getMoveQueue().push({ move: move.id, targets: [ target.getBattlerIndex() ], ignorePP: true });
           if (this.sameTurn) {
-            let movesetMove = user.moveset.find(m => m.moveId === move.id);
+            let movesetMove = user.moveset.find(m => m?.moveId === move.id);
             if (!movesetMove) { // account for any move that calls a ChargeAttr move when the ChargeAttr move does not exist in moveset
               movesetMove = new PokemonMove(move.id, 0, 0, true);
             }
-            user.scene.pushMovePhase(new MovePhase(user.scene, user, [ target.getBattlerIndex() ], movesetMove, true), this.followUpPriority);
+            user.scene.pushMovePhase(new MovePhase(user.scene, user, [ target.getBattlerIndex() ], movesetMove, true), this.followUpPriority!); // TODO: is this bang correct?
           }
           user.addTag(BattlerTagType.CHARGING, 1, move.id, user.id);
           resolve(true);
@@ -2399,7 +2400,7 @@ export class ChargeAttr extends OverrideMoveEffectAttr {
     });
   }
 
-  usedChargeEffect(user: Pokemon, target: Pokemon, move: Move): boolean {
+  usedChargeEffect(user: Pokemon, target: Pokemon | null, move: Move): boolean {
     if (!this.chargeEffect) {
       return false;
     }
@@ -2488,7 +2489,7 @@ export class DelayedAttackAttr extends OverrideMoveEffectAttr {
           resolve(true);
         });
       } else {
-        user.scene.ui.showText(i18next.t("moveTriggers:tookMoveAttack", {pokemonName: getPokemonNameWithAffix(user.scene.getPokemonById(target.id)), moveName: move.name}), null, () => resolve(true));
+        user.scene.ui.showText(i18next.t("moveTriggers:tookMoveAttack", {pokemonName: getPokemonNameWithAffix(user.scene.getPokemonById(target.id) ?? undefined), moveName: move.name}), null, () => resolve(true));
       }
     });
   }
@@ -2497,20 +2498,20 @@ export class DelayedAttackAttr extends OverrideMoveEffectAttr {
 export class StatChangeAttr extends MoveEffectAttr {
   public stats: BattleStat[];
   public levels: integer;
-  private condition: MoveConditionFunc;
+  private condition: MoveConditionFunc | null;
   private showMessage: boolean;
 
-  constructor(stats: BattleStat | BattleStat[], levels: integer, selfTarget?: boolean, condition?: MoveConditionFunc, showMessage: boolean = true, firstHitOnly: boolean = false, moveEffectTrigger: MoveEffectTrigger = MoveEffectTrigger.HIT, firstTargetOnly: boolean = false) {
+  constructor(stats: BattleStat | BattleStat[], levels: integer, selfTarget?: boolean, condition?: MoveConditionFunc | null, showMessage: boolean = true, firstHitOnly: boolean = false, moveEffectTrigger: MoveEffectTrigger = MoveEffectTrigger.HIT, firstTargetOnly: boolean = false) {
     super(selfTarget, moveEffectTrigger, firstHitOnly, false, firstTargetOnly);
     this.stats = typeof(stats) === "number"
       ? [ stats as BattleStat ]
       : stats as BattleStat[];
     this.levels = levels;
-    this.condition = condition || null;
+    this.condition = condition!; // TODO: is this bang correct?
     this.showMessage = showMessage;
   }
 
-  apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean | Promise<boolean> {
+  apply(user: Pokemon, target: Pokemon, move: Move, args?: any[]): boolean | Promise<boolean> {
     if (!super.apply(user, target, move, args) || (this.condition && !this.condition(user, target, move))) {
       return false;
     }
@@ -2574,7 +2575,7 @@ export class StatChangeAttr extends MoveEffectAttr {
 export class PostVictoryStatChangeAttr extends MoveAttr {
   private stats: BattleStat[];
   private levels: integer;
-  private condition: MoveConditionFunc;
+  private condition: MoveConditionFunc | null;
   private showMessage: boolean;
 
   constructor(stats: BattleStat | BattleStat[], levels: integer, selfTarget?: boolean, condition?: MoveConditionFunc, showMessage: boolean = true, firstHitOnly: boolean = false) {
@@ -2583,7 +2584,7 @@ export class PostVictoryStatChangeAttr extends MoveAttr {
       ? [ stats as BattleStat ]
       : stats as BattleStat[];
     this.levels = levels;
-    this.condition = condition || null;
+    this.condition = condition!; // TODO: is this bang correct?
     this.showMessage = showMessage;
   }
   applyPostVictory(user: Pokemon, target: Pokemon, move: Move): void {
@@ -2591,7 +2592,7 @@ export class PostVictoryStatChangeAttr extends MoveAttr {
       return;
     }
     const statChangeAttr = new StatChangeAttr(this.stats, this.levels, this.showMessage);
-    statChangeAttr.apply(user, target, move, undefined);
+    statChangeAttr.apply(user, target, move);
   }
 }
 
@@ -2751,7 +2752,7 @@ export class HpSplitAttr extends MoveEffectAttr {
         return resolve(false);
       }
 
-      const infoUpdates = [];
+      const infoUpdates: Promise<void>[] = [];
 
       const hpValue = Math.floor((target.hp + user.hp) / 2);
       if (user.hp < hpValue) {
@@ -2803,7 +2804,7 @@ export class LessPPMorePowerAttr extends VariablePowerAttr {
    */
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     const ppMax = move.pp;
-    const ppUsed = user.moveset.find((m) => m.moveId === move.id).ppUsed;
+    const ppUsed = user.moveset.find((m) => m?.moveId === move.id)?.ppUsed!; // TODO: is the bang correct?
 
     let ppRemains = ppMax - ppUsed;
     /** Reduce to 0 to avoid negative numbers if user has 1PP before attack and target has Ability.PRESSURE */
@@ -2870,6 +2871,7 @@ const beatUpFunc = (user: Pokemon, allyIndex: number): number => {
     }
     return (pokemon.species.getBaseStat(Stat.ATK) / 10) + 5;
   }
+  return 0;
 };
 
 export class BeatUpAttr extends VariablePowerAttr {
@@ -2896,7 +2898,7 @@ export class BeatUpAttr extends VariablePowerAttr {
 }
 
 const doublePowerChanceMessageFunc = (user: Pokemon, target: Pokemon, move: Move) => {
-  let message: string = null;
+  let message: string = "";
   user.scene.executeWithSeedOffset(() => {
     const rand = Utils.randSeedInt(100);
     if (rand < move.chance) {
@@ -2910,7 +2912,7 @@ export class DoublePowerChanceAttr extends VariablePowerAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     let rand: integer;
     user.scene.executeWithSeedOffset(() => rand = Utils.randSeedInt(100), user.scene.currentBattle.turn << 6, user.scene.waveSeed);
-    if (rand < move.chance) {
+    if (rand! < move.chance) {
       const power = args[0] as Utils.NumberHolder;
       power.value *= 2;
       return true;
@@ -2926,9 +2928,9 @@ export abstract class ConsecutiveUsePowerMultiplierAttr extends MovePowerMultipl
       const moveHistory = user.getLastXMoves(limit + 1).slice(1);
 
       let count = 0;
-      let turnMove: TurnMove;
+      let turnMove: TurnMove | undefined;
 
-      while (((turnMove = moveHistory.shift())?.move === move.id || (comboMoves.length && comboMoves.includes(turnMove?.move))) && (!resetOnFail || turnMove.result === MoveResult.SUCCESS)) {
+      while (((turnMove = moveHistory.shift())?.move === move.id || (comboMoves.length && comboMoves.includes(turnMove?.move!))) && (!resetOnFail || turnMove?.result === MoveResult.SUCCESS)) { // TODO: is this bang correct?
         if (count < (limit - 1)) {
           count++;
         } else if (resetOnLimit) {
@@ -3181,7 +3183,7 @@ const magnitudeMessageFunc = (user: Pokemon, target: Pokemon, move: Move) => {
 
     message = i18next.t("moveTriggers:magnitudeMessage", {magnitude: m + 4});
   }, user.scene.currentBattle.turn << 6, user.scene.waveSeed);
-  return message;
+  return message!;
 };
 
 export class MagnitudePowerAttr extends VariablePowerAttr {
@@ -3197,7 +3199,7 @@ export class MagnitudePowerAttr extends VariablePowerAttr {
 
     let m = 0;
     for (; m < magnitudeThresholds.length; m++) {
-      if (rand < magnitudeThresholds[m]) {
+      if (rand! < magnitudeThresholds[m]) {
         break;
       }
     }
@@ -3360,7 +3362,7 @@ export class SpitUpPowerAttr extends VariablePowerAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     const stockpilingTag = user.getTag(StockpilingTag);
 
-    if (stockpilingTag?.stockpiledCount > 0) {
+    if (stockpilingTag !== null && stockpilingTag.stockpiledCount > 0) {
       const power = args[0] as Utils.IntegerHolder;
       power.value = this.multiplier * stockpilingTag.stockpiledCount;
       return true;
@@ -3378,7 +3380,7 @@ export class SwallowHealAttr extends HealAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     const stockpilingTag = user.getTag(StockpilingTag);
 
-    if (stockpilingTag?.stockpiledCount > 0) {
+    if (stockpilingTag !== null && stockpilingTag?.stockpiledCount > 0) {
       const stockpiled = stockpilingTag.stockpiledCount;
       let healRatio: number;
 
@@ -3400,7 +3402,10 @@ export class SwallowHealAttr extends HealAttr {
   }
 }
 
-const hasStockpileStacksCondition: MoveConditionFunc = (user) => user.getTag(StockpilingTag)?.stockpiledCount > 0;
+const hasStockpileStacksCondition: MoveConditionFunc = (user) => {
+  const hasStockpilingTag = user.getTag(StockpilingTag);
+  return !!hasStockpilingTag && hasStockpilingTag.stockpiledCount > 0;
+};
 
 /**
  * Attribute used for multi-hit moves that increase power in increments of the
@@ -3471,13 +3476,13 @@ export class LastMoveDoublePowerAttr extends VariablePowerAttr {
     const enemy = user.getOpponent(0);
     const pokemonActed: Pokemon[] = [];
 
-    if (enemy.turnData.acted) {
+    if (enemy?.turnData.acted) {
       pokemonActed.push(enemy);
     }
 
     if (user.scene.currentBattle.double) {
       const userAlly = user.getAlly();
-      const enemyAlly = enemy.getAlly();
+      const enemyAlly = enemy?.getAlly();
 
       if (userAlly && userAlly.turnData.acted) {
         pokemonActed.push(userAlly);
@@ -3751,7 +3756,7 @@ export class VariableMoveTypeAttr extends MoveAttr {
 export class FormChangeItemTypeAttr extends VariableMoveTypeAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     if ([user.species.speciesId, user.fusionSpecies?.speciesId].includes(Species.ARCEUS) || [user.species.speciesId, user.fusionSpecies?.speciesId].includes(Species.SILVALLY)) {
-      const form = user.species.speciesId === Species.ARCEUS || user.species.speciesId === Species.SILVALLY ? user.formIndex : user.fusionSpecies.formIndex;
+      const form = user.species.speciesId === Species.ARCEUS || user.species.speciesId === Species.SILVALLY ? user.formIndex : user.fusionSpecies?.formIndex!; // TODO: is this bang correct?
 
       move.type = Type[Type[form]];
       return true;
@@ -3764,7 +3769,7 @@ export class FormChangeItemTypeAttr extends VariableMoveTypeAttr {
 export class TechnoBlastTypeAttr extends VariableMoveTypeAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     if ([user.species.speciesId, user.fusionSpecies?.speciesId].includes(Species.GENESECT)) {
-      const form = user.species.speciesId === Species.GENESECT ? user.formIndex : user.fusionSpecies.formIndex;
+      const form = user.species.speciesId === Species.GENESECT ? user.formIndex : user.fusionSpecies?.formIndex;
 
       switch (form) {
       case 1: // Shock Drive
@@ -3793,7 +3798,7 @@ export class TechnoBlastTypeAttr extends VariableMoveTypeAttr {
 export class AuraWheelTypeAttr extends VariableMoveTypeAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     if ([user.species.speciesId, user.fusionSpecies?.speciesId].includes(Species.MORPEKO)) {
-      const form = user.species.speciesId === Species.MORPEKO ? user.formIndex : user.fusionSpecies.formIndex;
+      const form = user.species.speciesId === Species.MORPEKO ? user.formIndex : user.fusionSpecies?.formIndex;
 
       switch (form) {
       case 1: // Hangry Mode
@@ -3813,7 +3818,7 @@ export class AuraWheelTypeAttr extends VariableMoveTypeAttr {
 export class RagingBullTypeAttr extends VariableMoveTypeAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     if ([user.species.speciesId, user.fusionSpecies?.speciesId].includes(Species.PALDEA_TAUROS)) {
-      const form = user.species.speciesId === Species.PALDEA_TAUROS ? user.formIndex : user.fusionSpecies.formIndex;
+      const form = user.species.speciesId === Species.PALDEA_TAUROS ? user.formIndex : user.fusionSpecies?.formIndex;
 
       switch (form) {
       case 1: // Blaze breed
@@ -3836,7 +3841,7 @@ export class RagingBullTypeAttr extends VariableMoveTypeAttr {
 export class IvyCudgelTypeAttr extends VariableMoveTypeAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     if ([user.species.speciesId, user.fusionSpecies?.speciesId].includes(Species.OGERPON)) {
-      const form = user.species.speciesId === Species.OGERPON ? user.formIndex : user.fusionSpecies.formIndex;
+      const form = user.species.speciesId === Species.OGERPON ? user.formIndex : user.fusionSpecies?.formIndex;
 
       switch (form) {
       case 1: // Wellspring Mask
@@ -4125,23 +4130,23 @@ export class DisableMoveAttr extends MoveEffectAttr {
     }
 
     const moveQueue = target.getLastXMoves();
-    let turnMove: TurnMove;
+    let turnMove: TurnMove | undefined;
     while (moveQueue.length) {
       turnMove = moveQueue.shift();
-      if (turnMove.virtual) {
+      if (turnMove?.virtual) {
         continue;
       }
 
-      const moveIndex = target.getMoveset().findIndex(m => m.moveId === turnMove.move);
+      const moveIndex = target.getMoveset().findIndex(m => m?.moveId === turnMove?.move);
       if (moveIndex === -1) {
         return false;
       }
 
       const disabledMove = target.getMoveset()[moveIndex];
-      target.summonData.disabledMove = disabledMove.moveId;
+      target.summonData.disabledMove = disabledMove?.moveId!; // TODO: is this bang correct?
       target.summonData.disabledTurns = 4;
 
-      user.scene.queueMessage(i18next.t("abilityTriggers:postDefendMoveDisable", { pokemonNameWithAffix: getPokemonNameWithAffix(target), moveName: disabledMove.getName()}));
+      user.scene.queueMessage(i18next.t("abilityTriggers:postDefendMoveDisable", { pokemonNameWithAffix: getPokemonNameWithAffix(target), moveName: disabledMove?.getName()}));
 
       return true;
     }
@@ -4150,26 +4155,28 @@ export class DisableMoveAttr extends MoveEffectAttr {
   }
 
   getCondition(): MoveConditionFunc {
-    return (user, target, move) => {
+    return (user, target, move): boolean => { // TODO: Not sure what to do here
       if (target.summonData.disabledMove || target.isMax()) {
         return false;
       }
 
       const moveQueue = target.getLastXMoves();
-      let turnMove: TurnMove;
+      let turnMove: TurnMove | undefined;
       while (moveQueue.length) {
         turnMove = moveQueue.shift();
-        if (turnMove.virtual) {
+        if (turnMove?.virtual) {
           continue;
         }
 
-        const move = target.getMoveset().find(m => m.moveId === turnMove.move);
+        const move = target.getMoveset().find(m => m?.moveId === turnMove?.move);
         if (!move) {
           continue;
         }
 
         return true;
       }
+
+      return false;
     };
   }
 
@@ -4242,13 +4249,13 @@ export class AddBattlerTagAttr extends MoveEffectAttr {
     return false;
   }
 
-  getCondition(): MoveConditionFunc {
+  getCondition(): MoveConditionFunc | null {
     return this.failOnOverlap
       ? (user, target, move) => !(this.selfTarget ? user : target).getTag(this.tagType)
       : null;
   }
 
-  getTagTargetBenefitScore(user: Pokemon, target: Pokemon, move: Move): integer {
+  getTagTargetBenefitScore(user: Pokemon, target: Pokemon, move: Move): integer | void {
     switch (this.tagType) {
     case BattlerTagType.RECHARGING:
     case BattlerTagType.PERISH_SONG:
@@ -4296,7 +4303,7 @@ export class AddBattlerTagAttr extends MoveEffectAttr {
     if (moveChance < 0) {
       moveChance = 100;
     }
-    return Math.floor(this.getTagTargetBenefitScore(user, target, move) * (moveChance / 100));
+    return Math.floor(this.getTagTargetBenefitScore(user, target, move)! * (moveChance / 100)); // TODO: is the bang correct?
   }
 }
 
@@ -4444,11 +4451,11 @@ export class ProtectAttr extends AddBattlerTagAttr {
     return ((user, target, move): boolean => {
       let timesUsed = 0;
       const moveHistory = user.getLastXMoves();
-      let turnMove: TurnMove;
+      let turnMove: TurnMove | undefined;
 
       while (moveHistory.length) {
         turnMove = moveHistory.shift();
-        if (!allMoves[turnMove.move].hasAttr(ProtectAttr) || turnMove.result !== MoveResult.SUCCESS) {
+        if (!allMoves[turnMove?.move!].hasAttr(ProtectAttr) || turnMove?.result !== MoveResult.SUCCESS) { // TODO: is the bang correct?
           break;
         }
         timesUsed++;
@@ -4521,11 +4528,11 @@ export class AddArenaTagAttr extends MoveEffectAttr {
   private failOnOverlap: boolean;
   public selfSideTarget: boolean;
 
-  constructor(tagType: ArenaTagType, turnCount?: integer, failOnOverlap: boolean = false, selfSideTarget: boolean = false) {
+  constructor(tagType: ArenaTagType, turnCount?: integer | null, failOnOverlap: boolean = false, selfSideTarget: boolean = false) {
     super(true, MoveEffectTrigger.POST_APPLY);
 
     this.tagType = tagType;
-    this.turnCount = turnCount;
+    this.turnCount = turnCount!; // TODO: is the bang correct?
     this.failOnOverlap = failOnOverlap;
     this.selfSideTarget = selfSideTarget;
   }
@@ -4543,7 +4550,7 @@ export class AddArenaTagAttr extends MoveEffectAttr {
     return false;
   }
 
-  getCondition(): MoveConditionFunc {
+  getCondition(): MoveConditionFunc | null {
     return this.failOnOverlap
       ? (user, target, move) => !user.scene.arena.getTagOnSide(this.tagType, target.isPlayer() ? ArenaTagSide.PLAYER : ArenaTagSide.ENEMY)
       : null;
@@ -4716,13 +4723,13 @@ export class SwapArenaTagsAttr extends MoveEffectAttr {
     if (tagPlayerTemp) {
       for (const swapTagsType of tagPlayerTemp) {
         user.scene.arena.removeTagOnSide(swapTagsType.tagType, ArenaTagSide.PLAYER, true);
-        user.scene.arena.addTag(swapTagsType.tagType, swapTagsType.turnCount, swapTagsType.sourceMove, swapTagsType.sourceId, ArenaTagSide.ENEMY, true);
+        user.scene.arena.addTag(swapTagsType.tagType, swapTagsType.turnCount, swapTagsType.sourceMove, swapTagsType.sourceId!, ArenaTagSide.ENEMY, true); // TODO: is the bang correct?
       }
     }
     if (tagEnemyTemp) {
       for (const swapTagsType of tagEnemyTemp) {
         user.scene.arena.removeTagOnSide(swapTagsType.tagType, ArenaTagSide.ENEMY, true);
-        user.scene.arena.addTag(swapTagsType.tagType, swapTagsType.turnCount, swapTagsType.sourceMove, swapTagsType.sourceId, ArenaTagSide.PLAYER, true);
+        user.scene.arena.addTag(swapTagsType.tagType, swapTagsType.turnCount, swapTagsType.sourceMove, swapTagsType.sourceId!, ArenaTagSide.PLAYER, true); // TODO: is the bang correct?
       }
     }
 
@@ -4836,7 +4843,7 @@ export class ForceSwitchOutAttr extends MoveEffectAttr {
 
 	  	if (switchOutTarget.hp > 0) {
         // for opponent switching out
-          user.scene.prependToPhase(new SwitchSummonPhase(user.scene, switchOutTarget.getFieldIndex(), user.scene.currentBattle.trainer.getNextSummonIndex((switchOutTarget as EnemyPokemon).trainerSlot), false, this.batonPass, false), MoveEndPhase);
+          user.scene.prependToPhase(new SwitchSummonPhase(user.scene, switchOutTarget.getFieldIndex(), (user.scene.currentBattle.trainer ? user.scene.currentBattle.trainer.getNextSummonIndex((switchOutTarget as EnemyPokemon).trainerSlot) : 0), false, this.batonPass, false), MoveEndPhase);
         }
 	  } else {
 	    // Switch out logic for everything else
@@ -4926,7 +4933,7 @@ export class RemoveTypeAttr extends MoveEffectAttr {
       return false;
     }
 
-    if (user.isTerastallized && user.getTeraType() === this.removedType) { // active tera types cannot be removed
+    if (user.isTerastallized() && user.getTeraType() === this.removedType) { // active tera types cannot be removed
       return false;
     }
 
@@ -5048,7 +5055,7 @@ export class FirstMoveTypeAttr extends MoveEffectAttr {
       return false;
     }
 
-    const firstMoveType = target.getMoveset()[0].getMove().type;
+    const firstMoveType = target.getMoveset()[0]?.getMove().type!; // TODO: is this bang correct?
     user.summonData.types = [ firstMoveType ];
     user.scene.queueMessage(i18next.t("battle:transformedIntoType", {pokemonName: getPokemonNameWithAffix(user), type: i18next.t(`pokemonInfo:Type.${Type[firstMoveType]}`)}));
 
@@ -5057,21 +5064,21 @@ export class FirstMoveTypeAttr extends MoveEffectAttr {
 }
 
 export class RandomMovesetMoveAttr extends OverrideMoveEffectAttr {
-  private enemyMoveset: boolean;
+  private enemyMoveset: boolean | null;
 
   constructor(enemyMoveset?: boolean) {
     super();
 
-    this.enemyMoveset = enemyMoveset;
+    this.enemyMoveset = enemyMoveset!; // TODO: is this bang correct?
   }
 
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     const moveset = (!this.enemyMoveset ? user : target).getMoveset();
-    const moves = moveset.filter(m => !m.getMove().hasFlag(MoveFlags.IGNORE_VIRTUAL));
+    const moves = moveset.filter(m => !m?.getMove().hasFlag(MoveFlags.IGNORE_VIRTUAL));
     if (moves.length) {
       const move = moves[user.randSeedInt(moves.length)];
-      const moveIndex = moveset.findIndex(m => m.moveId === move.moveId);
-      const moveTargets = getMoveTargets(user, move.moveId);
+      const moveIndex = moveset.findIndex(m => m?.moveId === move?.moveId);
+      const moveTargets = getMoveTargets(user, move?.moveId!); // TODO: is this bang correct?
       if (!moveTargets.targets.length) {
         return false;
       }
@@ -5092,8 +5099,8 @@ export class RandomMovesetMoveAttr extends OverrideMoveEffectAttr {
       }
       }
       const targets = selectTargets;
-      user.getMoveQueue().push({ move: move.moveId, targets: targets, ignorePP: true });
-      user.scene.unshiftPhase(new MovePhase(user.scene, user, targets, moveset[moveIndex], true));
+      user.getMoveQueue().push({ move: move?.moveId!, targets: targets, ignorePP: true }); // TODO: is this bang correct?
+      user.scene.unshiftPhase(new MovePhase(user.scene, user, targets, moveset[moveIndex]!, true)); // There's a PR to re-do the move(s) that use this Attr, gonna put `!` for now
       return true;
     }
 
@@ -5335,12 +5342,12 @@ export class ReducePpMoveAttr extends MoveEffectAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     // Null checks can be skipped due to condition function
     const lastMove = target.getLastXMoves().find(() => true);
-    const movesetMove = target.getMoveset().find(m => m.moveId === lastMove.move);
-    const lastPpUsed = movesetMove.ppUsed;
-    movesetMove.ppUsed = Math.min(movesetMove.ppUsed + this.reduction, movesetMove.getMovePp());
+    const movesetMove = target.getMoveset().find(m => m?.moveId === lastMove?.move);
+    const lastPpUsed = movesetMove?.ppUsed!; // TODO: is the bang correct?
+    movesetMove!.ppUsed = Math.min((movesetMove?.ppUsed!) + this.reduction, movesetMove?.getMovePp()!); // TODO: is the bang correct?
 
-    const message = i18next.t("battle:ppReduced", {targetName: getPokemonNameWithAffix(target), moveName: movesetMove.getName(), reduction: movesetMove.ppUsed - lastPpUsed});
-    user.scene.eventTarget.dispatchEvent(new MoveUsedEvent(target?.id, movesetMove.getMove(), movesetMove.ppUsed));
+    const message = i18next.t("battle:ppReduced", {targetName: getPokemonNameWithAffix(target), moveName: movesetMove?.getName(), reduction: (movesetMove?.ppUsed!) - lastPpUsed}); // TODO: is the bang correct?
+    user.scene.eventTarget.dispatchEvent(new MoveUsedEvent(target?.id, movesetMove?.getMove()!, movesetMove?.ppUsed!)); // TODO: are these bangs correct?
     user.scene.queueMessage(message);
 
     return true;
@@ -5350,7 +5357,7 @@ export class ReducePpMoveAttr extends MoveEffectAttr {
     return (user, target, move) => {
       const lastMove = target.getLastXMoves().find(() => true);
       if (lastMove) {
-        const movesetMove = target.getMoveset().find(m => m.moveId === lastMove.move);
+        const movesetMove = target.getMoveset().find(m => m?.moveId === lastMove.move);
         return !!movesetMove?.getPpRatio();
       }
       return false;
@@ -5360,7 +5367,7 @@ export class ReducePpMoveAttr extends MoveEffectAttr {
   getTargetBenefitScore(user: Pokemon, target: Pokemon, move: Move): number {
     const lastMove = target.getLastXMoves().find(() => true);
     if (lastMove) {
-      const movesetMove = target.getMoveset().find(m => m.moveId === lastMove.move);
+      const movesetMove = target.getMoveset().find(m => m?.moveId === lastMove.move);
       if (movesetMove) {
         const maxPp = movesetMove.getMovePp();
         const ppLeft = maxPp - movesetMove.ppUsed;
@@ -5397,7 +5404,7 @@ export class AttackReducePpMoveAttr extends ReducePpMoveAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     const lastMove = target.getLastXMoves().find(() => true);
     if (lastMove) {
-      const movesetMove = target.getMoveset().find(m => m.moveId === lastMove.move);
+      const movesetMove = target.getMoveset().find(m => m?.moveId === lastMove.move);
       if (Boolean(movesetMove?.getPpRatio())) {
         super.apply(user, target, move, args);
       }
@@ -5443,7 +5450,7 @@ export class MovesetCopyMoveAttr extends OverrideMoveEffectAttr {
 
     const copiedMove = allMoves[targetMoves[0].move];
 
-    const thisMoveIndex = user.getMoveset().findIndex(m => m.moveId === move.id);
+    const thisMoveIndex = user.getMoveset().findIndex(m => m?.moveId === move.id);
 
     if (thisMoveIndex === -1) {
       return false;
@@ -5494,7 +5501,7 @@ export class SketchAttr extends MoveEffectAttr {
     }
 
     const sketchedMove = allMoves[targetMove.move];
-    const sketchIndex = user.getMoveset().findIndex(m => m.moveId === move.id);
+    const sketchIndex = user.getMoveset().findIndex(m => m?.moveId === move.id);
     if (sketchIndex === -1) {
       return false;
     }
@@ -5533,7 +5540,7 @@ export class SketchAttr extends MoveEffectAttr {
         return false;
       }
 
-      if (user.getMoveset().find(m => m.moveId === targetMove.move)) {
+      if (user.getMoveset().find(m => m?.moveId === targetMove.move)) {
         return false;
       }
 
@@ -5722,7 +5729,7 @@ export class TransformAttr extends MoveEffectAttr {
       user.summonData.fusionGender = target.getFusionGender();
       user.summonData.stats = [ user.stats[Stat.HP] ].concat(target.stats.slice(1));
       user.summonData.battleStats = target.summonData.battleStats.slice(0);
-      user.summonData.moveset = target.getMoveset().map(m => new PokemonMove(m.moveId, m.ppUsed, m.ppUp));
+      user.summonData.moveset = target.getMoveset().map(m => new PokemonMove(m?.moveId!, m?.ppUsed, m?.ppUp)); // TODO: is this bang correct?
       user.summonData.types = target.getTypes();
 
       user.scene.queueMessage(i18next.t("moveTriggers:transformedIntoTarget", {pokemonName: getPokemonNameWithAffix(user), targetName: getPokemonNameWithAffix(target)}));
@@ -5790,7 +5797,7 @@ export class LastResortAttr extends MoveAttr {
   getCondition(): MoveConditionFunc {
     return (user: Pokemon, target: Pokemon, move: Move) => {
       const uniqueUsedMoveIds = new Set<Moves>();
-      const movesetMoveIds = user.getMoveset().map(m => m.moveId);
+      const movesetMoveIds = user.getMoveset().map(m => m?.moveId);
       user.getMoveHistory().map(m => {
         if (m.move !== move.id && movesetMoveIds.find(mm => mm === m.move)) {
           uniqueUsedMoveIds.add(m.move);
@@ -5864,7 +5871,7 @@ const targetSleptOrComatoseCondition: MoveConditionFunc = (user: Pokemon, target
 
 export type MoveAttrFilter = (attr: MoveAttr) => boolean;
 
-function applyMoveAttrsInternal(attrFilter: MoveAttrFilter, user: Pokemon, target: Pokemon, move: Move, args: any[]): Promise<void> {
+function applyMoveAttrsInternal(attrFilter: MoveAttrFilter, user: Pokemon | null, target: Pokemon | null, move: Move, args: any[]): Promise<void> {
   return new Promise(resolve => {
     const attrPromises: Promise<boolean>[] = [];
     const moveAttrs = move.attrs.filter(a => attrFilter(a));
@@ -5878,11 +5885,11 @@ function applyMoveAttrsInternal(attrFilter: MoveAttrFilter, user: Pokemon, targe
   });
 }
 
-export function applyMoveAttrs(attrType: Constructor<MoveAttr>, user: Pokemon, target: Pokemon, move: Move, ...args: any[]): Promise<void> {
+export function applyMoveAttrs(attrType: Constructor<MoveAttr>, user: Pokemon | null, target: Pokemon | null, move: Move, ...args: any[]): Promise<void> {
   return applyMoveAttrsInternal((attr: MoveAttr) => attr instanceof attrType, user, target, move, args);
 }
 
-export function applyFilteredMoveAttrs(attrFilter: MoveAttrFilter, user: Pokemon, target: Pokemon, move: Move, ...args: any[]): Promise<void> {
+export function applyFilteredMoveAttrs(attrFilter: MoveAttrFilter, user: Pokemon, target: Pokemon | null, move: Move, ...args: any[]): Promise<void> {
   return applyMoveAttrsInternal(attrFilter, user, target, move, args);
 }
 
@@ -6889,7 +6896,7 @@ export function initMoves() {
       .unimplemented(),
     new SelfStatusMove(Moves.REFRESH, Type.NORMAL, -1, 20, -1, 0, 3)
       .attr(HealStatusEffectAttr, true, StatusEffect.PARALYSIS, StatusEffect.POISON, StatusEffect.TOXIC, StatusEffect.BURN)
-      .condition((user, target, move) => user.status && (user.status.effect === StatusEffect.PARALYSIS || user.status.effect === StatusEffect.POISON || user.status.effect === StatusEffect.TOXIC || user.status.effect === StatusEffect.BURN)),
+      .condition((user, target, move) => !!user.status && (user.status.effect === StatusEffect.PARALYSIS || user.status.effect === StatusEffect.POISON || user.status.effect === StatusEffect.TOXIC || user.status.effect === StatusEffect.BURN)),
     new SelfStatusMove(Moves.GRUDGE, Type.GHOST, -1, 5, -1, 0, 3)
       .unimplemented(),
     new SelfStatusMove(Moves.SNATCH, Type.DARK, -1, 10, -1, 4, 3)
@@ -6952,7 +6959,7 @@ export function initMoves() {
       .attr(FlinchAttr),
     new AttackMove(Moves.WEATHER_BALL, Type.NORMAL, MoveCategory.SPECIAL, 50, 100, 10, -1, 0, 3)
       .attr(WeatherBallTypeAttr)
-      .attr(MovePowerMultiplierAttr, (user, target, move) => [WeatherType.SUNNY, WeatherType.RAIN, WeatherType.SANDSTORM, WeatherType.HAIL, WeatherType.SNOW, WeatherType.FOG, WeatherType.HEAVY_RAIN, WeatherType.HARSH_SUN].includes(user.scene.arena.weather?.weatherType) && !user.scene.arena.weather?.isEffectSuppressed(user.scene) ? 2 : 1)
+      .attr(MovePowerMultiplierAttr, (user, target, move) => [WeatherType.SUNNY, WeatherType.RAIN, WeatherType.SANDSTORM, WeatherType.HAIL, WeatherType.SNOW, WeatherType.FOG, WeatherType.HEAVY_RAIN, WeatherType.HARSH_SUN].includes(user.scene.arena.weather?.weatherType!) && !user.scene.arena.weather?.isEffectSuppressed(user.scene) ? 2 : 1) // TODO: is this bang correct?
       .ballBombMove(),
     new StatusMove(Moves.AROMATHERAPY, Type.GRASS, -1, 5, -1, 0, 3)
       .attr(PartyStatusCureAttr, i18next.t("moveTriggers:soothingAromaWaftedThroughArea"), Abilities.SAP_SIPPER)
@@ -7120,7 +7127,7 @@ export function initMoves() {
     new AttackMove(Moves.CLOSE_COMBAT, Type.FIGHTING, MoveCategory.PHYSICAL, 120, 100, 5, -1, 0, 4)
       .attr(StatChangeAttr, [ BattleStat.DEF, BattleStat.SPDEF ], -1, true),
     new AttackMove(Moves.PAYBACK, Type.DARK, MoveCategory.PHYSICAL, 50, 100, 10, -1, 0, 4)
-      .attr(MovePowerMultiplierAttr, (user, target, move) => target.getLastXMoves(1).find(m => m.turn === target.scene.currentBattle.turn) || user.scene.currentBattle.turnCommands[target.getBattlerIndex()].command === Command.BALL ? 2 : 1),
+      .attr(MovePowerMultiplierAttr, (user, target, move) => target.getLastXMoves(1).find(m => m.turn === target.scene.currentBattle.turn) || user.scene.currentBattle.turnCommands[target.getBattlerIndex()]?.command === Command.BALL ? 2 : 1),
     new AttackMove(Moves.ASSURANCE, Type.DARK, MoveCategory.PHYSICAL, 60, 100, 10, -1, 0, 4)
       .attr(MovePowerMultiplierAttr, (user, target, move) => target.turnData.damageTaken > 0 ? 2 : 1),
     new StatusMove(Moves.EMBARGO, Type.DARK, 100, 15, -1, 0, 4)
@@ -7135,7 +7142,7 @@ export function initMoves() {
         if (user.status?.effect && isNonVolatileStatusEffect(user.status.effect)) {
           statusToApply = user.status.effect;
         }
-        return statusToApply && target.canSetStatus(statusToApply, false, false, user);
+        return !!statusToApply && target.canSetStatus(statusToApply, false, false, user);
       }
       ),
     new AttackMove(Moves.TRUMP_CARD, Type.NORMAL, MoveCategory.SPECIAL, -1, -1, 5, -1, 0, 4)
@@ -7173,7 +7180,7 @@ export function initMoves() {
     new StatusMove(Moves.WORRY_SEED, Type.GRASS, 100, 10, -1, 0, 4)
       .attr(AbilityChangeAttr, Abilities.INSOMNIA),
     new AttackMove(Moves.SUCKER_PUNCH, Type.DARK, MoveCategory.PHYSICAL, 70, 100, 5, -1, 1, 4)
-      .condition((user, target, move) => user.scene.currentBattle.turnCommands[target.getBattlerIndex()].command === Command.FIGHT && !target.turnData.acted && allMoves[user.scene.currentBattle.turnCommands[target.getBattlerIndex()].move.move].category !== MoveCategory.STATUS),
+      .condition((user, target, move) => user.scene.currentBattle.turnCommands[target.getBattlerIndex()]?.command === Command.FIGHT && !target.turnData.acted && allMoves[user.scene.currentBattle.turnCommands[target.getBattlerIndex()]?.move?.move!].category !== MoveCategory.STATUS), // TODO: is this bang correct?
     new StatusMove(Moves.TOXIC_SPIKES, Type.POISON, -1, 20, -1, 0, 4)
       .attr(AddArenaTrapTagAttr, ArenaTagType.TOXIC_SPIKES)
       .target(MoveTarget.ENEMY_SIDE),
@@ -8016,7 +8023,7 @@ export function initMoves() {
     new AttackMove(Moves.SMART_STRIKE, Type.STEEL, MoveCategory.PHYSICAL, 70, -1, 10, -1, 0, 7),
     new StatusMove(Moves.PURIFY, Type.POISON, -1, 20, -1, 0, 7)
       .condition(
-        (user: Pokemon, target: Pokemon, move: Move) => isNonVolatileStatusEffect(target.status?.effect))
+        (user: Pokemon, target: Pokemon, move: Move) => isNonVolatileStatusEffect(target.status?.effect!)) // TODO: is this bang correct?
       .attr(HealAttr, 0.5)
       .attr(HealStatusEffectAttr, false, ...getNonVolatileStatusEffects())
       .triageMove(),
@@ -8738,7 +8745,7 @@ export function initMoves() {
       .slicingMove(),
     new AttackMove(Moves.HYDRO_STEAM, Type.WATER, MoveCategory.SPECIAL, 80, 100, 15, -1, 0, 9)
       .attr(IgnoreWeatherTypeDebuffAttr, WeatherType.SUNNY)
-      .attr(MovePowerMultiplierAttr, (user, target, move) => [WeatherType.SUNNY, WeatherType.HARSH_SUN].includes(user.scene.arena.weather?.weatherType) && !user.scene.arena.weather?.isEffectSuppressed(user.scene) ? 1.5 : 1),
+      .attr(MovePowerMultiplierAttr, (user, target, move) => [WeatherType.SUNNY, WeatherType.HARSH_SUN].includes(user.scene.arena.weather?.weatherType!) && !user.scene.arena.weather?.isEffectSuppressed(user.scene) ? 1.5 : 1), // TODO: is this bang correct?
     new AttackMove(Moves.RUINATION, Type.DARK, MoveCategory.SPECIAL, -1, 90, 10, -1, 0, 9)
       .attr(TargetHalfHpDamageAttr),
     new AttackMove(Moves.COLLISION_COURSE, Type.FIGHTING, MoveCategory.PHYSICAL, 100, 100, 5, -1, 0, 9)
@@ -8846,7 +8853,7 @@ export function initMoves() {
     new SelfStatusMove(Moves.BURNING_BULWARK, Type.FIRE, -1, 10, -1, 4, 9)
       .attr(ProtectAttr, BattlerTagType.BURNING_BULWARK),
     new AttackMove(Moves.THUNDERCLAP, Type.ELECTRIC, MoveCategory.SPECIAL, 70, 100, 5, -1, 1, 9)
-      .condition((user, target, move) => user.scene.currentBattle.turnCommands[target.getBattlerIndex()].command === Command.FIGHT && !target.turnData.acted && allMoves[user.scene.currentBattle.turnCommands[target.getBattlerIndex()].move.move].category !== MoveCategory.STATUS),
+      .condition((user, target, move) => user.scene.currentBattle.turnCommands[target.getBattlerIndex()]?.command === Command.FIGHT && !target.turnData.acted && allMoves[user.scene.currentBattle.turnCommands[target.getBattlerIndex()]?.move?.move!].category !== MoveCategory.STATUS), // TODO: is this bang correct?
     new AttackMove(Moves.MIGHTY_CLEAVE, Type.ROCK, MoveCategory.PHYSICAL, 95, 100, 5, -1, 0, 9)
       .slicingMove()
       .ignoresProtect(),
@@ -8873,7 +8880,7 @@ export function initMoves() {
       .partial(),
     new AttackMove(Moves.UPPER_HAND, Type.FIGHTING, MoveCategory.PHYSICAL, 65, 100, 15, 100, 3, 9)
       .attr(FlinchAttr)
-      .condition((user, target, move) => user.scene.currentBattle.turnCommands[target.getBattlerIndex()].command === Command.FIGHT && !target.turnData.acted && allMoves[user.scene.currentBattle.turnCommands[target.getBattlerIndex()].move.move].category !== MoveCategory.STATUS && allMoves[user.scene.currentBattle.turnCommands[target.getBattlerIndex()].move.move].priority > 0 )
+      .condition((user, target, move) => user.scene.currentBattle.turnCommands[target.getBattlerIndex()]?.command === Command.FIGHT && !target.turnData.acted && allMoves[user.scene.currentBattle.turnCommands[target.getBattlerIndex()]?.move?.move!].category !== MoveCategory.STATUS && allMoves[user.scene.currentBattle.turnCommands[target.getBattlerIndex()]?.move?.move!].priority > 0 ) // TODO: is this bang correct?
       //TODO: Should also apply when target move priority increased by ability ex. gale wings
       .partial(),
     new AttackMove(Moves.MALIGNANT_CHAIN, Type.POISON, MoveCategory.SPECIAL, 100, 100, 5, 50, 0, 9)
diff --git a/src/data/nature.ts b/src/data/nature.ts
index 1ae3b76a6b6..72e5bb7863c 100644
--- a/src/data/nature.ts
+++ b/src/data/nature.ts
@@ -15,8 +15,8 @@ export function getNatureName(nature: Nature, includeStatEffects: boolean = fals
   }
   if (includeStatEffects) {
     const stats = Utils.getEnumValues(Stat).slice(1);
-    let increasedStat: Stat = null;
-    let decreasedStat: Stat = null;
+    let increasedStat: Stat | null = null;
+    let decreasedStat: Stat | null = null;
     for (const stat of stats) {
       const multiplier = getNatureStatMultiplier(nature, stat);
       if (multiplier > 1) {
diff --git a/src/data/pokemon-evolutions.ts b/src/data/pokemon-evolutions.ts
index 236d174492f..e7baf608b97 100644
--- a/src/data/pokemon-evolutions.ts
+++ b/src/data/pokemon-evolutions.ts
@@ -59,26 +59,26 @@ export type EvolutionConditionEnforceFunc = (p: Pokemon) => void;
 
 export class SpeciesFormEvolution {
   public speciesId: Species;
-  public preFormKey: string;
-  public evoFormKey: string;
+  public preFormKey: string | null;
+  public evoFormKey: string | null;
   public level: integer;
-  public item: EvolutionItem;
-  public condition: SpeciesEvolutionCondition;
-  public wildDelay: SpeciesWildEvolutionDelay;
+  public item: EvolutionItem | null;
+  public condition: SpeciesEvolutionCondition | null;
+  public wildDelay: SpeciesWildEvolutionDelay | null;
 
-  constructor(speciesId: Species, preFormKey: string, evoFormKey: string, level: integer, item: EvolutionItem, condition: SpeciesEvolutionCondition, wildDelay?: SpeciesWildEvolutionDelay) {
+  constructor(speciesId: Species, preFormKey: string | null, evoFormKey: string | null, level: integer, item: EvolutionItem | null, condition: SpeciesEvolutionCondition | null, wildDelay?: SpeciesWildEvolutionDelay | null) {
     this.speciesId = speciesId;
     this.preFormKey = preFormKey;
     this.evoFormKey = evoFormKey;
     this.level = level;
     this.item = item || EvolutionItem.NONE;
     this.condition = condition;
-    this.wildDelay = wildDelay || SpeciesWildEvolutionDelay.NONE;
+    this.wildDelay = wildDelay!; // TODO: is this bang correct?
   }
 }
 
 export class SpeciesEvolution extends SpeciesFormEvolution {
-  constructor(speciesId: Species, level: integer, item: EvolutionItem, condition: SpeciesEvolutionCondition, wildDelay?: SpeciesWildEvolutionDelay) {
+  constructor(speciesId: Species, level: integer, item: EvolutionItem | null, condition: SpeciesEvolutionCondition | null, wildDelay?: SpeciesWildEvolutionDelay | null) {
     super(speciesId, null, null, level, item, condition, wildDelay);
   }
 }
@@ -95,7 +95,7 @@ export class FusionSpeciesFormEvolution extends SpeciesFormEvolution {
 
 export class SpeciesEvolutionCondition {
   public predicate: EvolutionConditionPredicate;
-  public enforceFunc: EvolutionConditionEnforceFunc;
+  public enforceFunc: EvolutionConditionEnforceFunc | undefined;
 
   constructor(predicate: EvolutionConditionPredicate, enforceFunc?: EvolutionConditionEnforceFunc) {
     this.predicate = predicate;
@@ -1264,17 +1264,17 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesEvolution(Species.EXEGGUTOR, 1, EvolutionItem.LEAF_STONE, null, SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.TANGELA]: [
-    new SpeciesEvolution(Species.TANGROWTH, 34, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.ANCIENT_POWER).length > 0), SpeciesWildEvolutionDelay.LONG)
+    new SpeciesEvolution(Species.TANGROWTH, 34, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.ANCIENT_POWER).length > 0), SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.LICKITUNG]: [
-    new SpeciesEvolution(Species.LICKILICKY, 32, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.ROLLOUT).length > 0), SpeciesWildEvolutionDelay.LONG)
+    new SpeciesEvolution(Species.LICKILICKY, 32, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.ROLLOUT).length > 0), SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.STARYU]: [
     new SpeciesEvolution(Species.STARMIE, 1, EvolutionItem.WATER_STONE, null, SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.EEVEE]: [
-    new SpeciesFormEvolution(Species.SYLVEON, "", "", 1, null, new SpeciesFriendshipEvolutionCondition(70, p => !!p.getMoveset().find(m => m.getMove().type === Type.FAIRY)), SpeciesWildEvolutionDelay.LONG),
-    new SpeciesFormEvolution(Species.SYLVEON, "partner", "", 1, null, new SpeciesFriendshipEvolutionCondition(70, p => !!p.getMoveset().find(m => m.getMove().type === Type.FAIRY)), SpeciesWildEvolutionDelay.LONG),
+    new SpeciesFormEvolution(Species.SYLVEON, "", "", 1, null, new SpeciesFriendshipEvolutionCondition(70, p => !!p.getMoveset().find(m => m?.getMove().type === Type.FAIRY)), SpeciesWildEvolutionDelay.LONG),
+    new SpeciesFormEvolution(Species.SYLVEON, "partner", "", 1, null, new SpeciesFriendshipEvolutionCondition(70, p => !!p.getMoveset().find(m => m?.getMove().type === Type.FAIRY)), SpeciesWildEvolutionDelay.LONG),
     new SpeciesFormEvolution(Species.ESPEON, "", "", 1, null, new SpeciesFriendshipEvolutionCondition(70, p => p.scene.arena.getTimeOfDay() === TimeOfDay.DAY), SpeciesWildEvolutionDelay.LONG),
     new SpeciesFormEvolution(Species.ESPEON, "partner", "", 1, null, new SpeciesFriendshipEvolutionCondition(70, p => p.scene.arena.getTimeOfDay() === TimeOfDay.DAY), SpeciesWildEvolutionDelay.LONG),
     new SpeciesFormEvolution(Species.UMBREON, "", "", 1, null, new SpeciesFriendshipEvolutionCondition(70, p => p.scene.arena.getTimeOfDay() === TimeOfDay.NIGHT), SpeciesWildEvolutionDelay.LONG),
@@ -1294,13 +1294,13 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesEvolution(Species.TOGEKISS, 1, EvolutionItem.SHINY_STONE, null, SpeciesWildEvolutionDelay.VERY_LONG)
   ],
   [Species.AIPOM]: [
-    new SpeciesEvolution(Species.AMBIPOM, 32, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.DOUBLE_HIT).length > 0), SpeciesWildEvolutionDelay.LONG)
+    new SpeciesEvolution(Species.AMBIPOM, 32, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.DOUBLE_HIT).length > 0), SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.SUNKERN]: [
     new SpeciesEvolution(Species.SUNFLORA, 1, EvolutionItem.SUN_STONE, null, SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.YANMA]: [
-    new SpeciesEvolution(Species.YANMEGA, 33, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.ANCIENT_POWER).length > 0), SpeciesWildEvolutionDelay.LONG)
+    new SpeciesEvolution(Species.YANMEGA, 33, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.ANCIENT_POWER).length > 0), SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.MURKROW]: [
     new SpeciesEvolution(Species.HONCHKROW, 1, EvolutionItem.DUSK_STONE, null, SpeciesWildEvolutionDelay.VERY_LONG)
@@ -1309,17 +1309,17 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesEvolution(Species.MISMAGIUS, 1, EvolutionItem.DUSK_STONE, null, SpeciesWildEvolutionDelay.VERY_LONG)
   ],
   [Species.GIRAFARIG]: [
-    new SpeciesEvolution(Species.FARIGIRAF, 32, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.TWIN_BEAM).length > 0), SpeciesWildEvolutionDelay.LONG)
+    new SpeciesEvolution(Species.FARIGIRAF, 32, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.TWIN_BEAM).length > 0), SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.DUNSPARCE]: [
     new SpeciesFormEvolution(Species.DUDUNSPARCE, "", "three-segment", 32, null, new SpeciesEvolutionCondition(p => {
       let ret = false;
-      if (p.moveset.filter(m => m.moveId === Moves.HYPER_DRILL).length > 0) {
+      if (p.moveset.filter(m => m?.moveId === Moves.HYPER_DRILL).length > 0) {
         p.scene.executeWithSeedOffset(() => ret = !Utils.randSeedInt(4), p.id);
       }
       return ret;
     }), SpeciesWildEvolutionDelay.LONG),
-    new SpeciesEvolution(Species.DUDUNSPARCE, 32, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.HYPER_DRILL).length > 0), SpeciesWildEvolutionDelay.LONG)
+    new SpeciesEvolution(Species.DUDUNSPARCE, 32, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.HYPER_DRILL).length > 0), SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.GLIGAR]: [
     new SpeciesEvolution(Species.GLISCOR, 1, null, new SpeciesEvolutionCondition(p => p.scene.arena.getTimeOfDay() === TimeOfDay.NIGHT /* Razor fang at night*/), SpeciesWildEvolutionDelay.LONG)
@@ -1331,10 +1331,10 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesEvolution(Species.URSALUNA, 1, EvolutionItem.PEAT_BLOCK, null, SpeciesWildEvolutionDelay.VERY_LONG) //Ursaring does not evolve into Bloodmoon Ursaluna
   ],
   [Species.PILOSWINE]: [
-    new SpeciesEvolution(Species.MAMOSWINE, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.ANCIENT_POWER).length > 0), SpeciesWildEvolutionDelay.VERY_LONG)
+    new SpeciesEvolution(Species.MAMOSWINE, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.ANCIENT_POWER).length > 0), SpeciesWildEvolutionDelay.VERY_LONG)
   ],
   [Species.STANTLER]: [
-    new SpeciesEvolution(Species.WYRDEER, 25, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.PSYSHIELD_BASH).length > 0), SpeciesWildEvolutionDelay.VERY_LONG)
+    new SpeciesEvolution(Species.WYRDEER, 25, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.PSYSHIELD_BASH).length > 0), SpeciesWildEvolutionDelay.VERY_LONG)
   ],
   [Species.LOMBRE]: [
     new SpeciesEvolution(Species.LUDICOLO, 1, EvolutionItem.WATER_STONE, null, SpeciesWildEvolutionDelay.LONG)
@@ -1352,11 +1352,11 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesEvolution(Species.ROSERADE, 1, EvolutionItem.SHINY_STONE, null, SpeciesWildEvolutionDelay.VERY_LONG)
   ],
   [Species.BONSLY]: [
-    new SpeciesEvolution(Species.SUDOWOODO, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.MIMIC).length > 0), SpeciesWildEvolutionDelay.MEDIUM)
+    new SpeciesEvolution(Species.SUDOWOODO, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.MIMIC).length > 0), SpeciesWildEvolutionDelay.MEDIUM)
   ],
   [Species.MIME_JR]: [
-    new SpeciesEvolution(Species.GALAR_MR_MIME, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.MIMIC).length > 0 && (p.scene.arena.biomeType === Biome.ICE_CAVE || p.scene.arena.biomeType === Biome.SNOWY_FOREST)), SpeciesWildEvolutionDelay.MEDIUM),
-    new SpeciesEvolution(Species.MR_MIME, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.MIMIC).length > 0), SpeciesWildEvolutionDelay.MEDIUM)
+    new SpeciesEvolution(Species.GALAR_MR_MIME, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.MIMIC).length > 0 && (p.scene.arena.biomeType === Biome.ICE_CAVE || p.scene.arena.biomeType === Biome.SNOWY_FOREST)), SpeciesWildEvolutionDelay.MEDIUM),
+    new SpeciesEvolution(Species.MR_MIME, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.MIMIC).length > 0), SpeciesWildEvolutionDelay.MEDIUM)
   ],
   [Species.PANSAGE]: [
     new SpeciesEvolution(Species.SIMISAGE, 1, EvolutionItem.LEAF_STONE, null, SpeciesWildEvolutionDelay.LONG)
@@ -1411,10 +1411,10 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesFormEvolution(Species.LYCANROC, "", "midnight", 25, null, new SpeciesEvolutionCondition(p => (p.scene.arena.getTimeOfDay() === TimeOfDay.DUSK || p.scene.arena.getTimeOfDay() === TimeOfDay.NIGHT) && (p.formIndex === 0)), null)
   ],
   [Species.STEENEE]: [
-    new SpeciesEvolution(Species.TSAREENA, 28, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.STOMP).length > 0), SpeciesWildEvolutionDelay.LONG)
+    new SpeciesEvolution(Species.TSAREENA, 28, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.STOMP).length > 0), SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.POIPOLE]: [
-    new SpeciesEvolution(Species.NAGANADEL, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.DRAGON_PULSE).length > 0), SpeciesWildEvolutionDelay.LONG)
+    new SpeciesEvolution(Species.NAGANADEL, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.DRAGON_PULSE).length > 0), SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.ALOLA_SANDSHREW]: [
     new SpeciesEvolution(Species.ALOLA_SANDSLASH, 1, EvolutionItem.ICE_STONE, null, SpeciesWildEvolutionDelay.LONG)
@@ -1428,7 +1428,7 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesEvolution(Species.APPLETUN, 1, EvolutionItem.SWEET_APPLE, null, SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.CLOBBOPUS]: [
-    new SpeciesEvolution(Species.GRAPPLOCT, 35, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.TAUNT).length > 0), SpeciesWildEvolutionDelay.MEDIUM)
+    new SpeciesEvolution(Species.GRAPPLOCT, 35, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.TAUNT).length > 0), SpeciesWildEvolutionDelay.MEDIUM)
   ],
   [Species.SINISTEA]: [
     new SpeciesFormEvolution(Species.POLTEAGEIST, "phony", "phony", 1, EvolutionItem.CRACKED_POT, null, SpeciesWildEvolutionDelay.LONG),
@@ -1462,7 +1462,7 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesEvolution(Species.HISUI_ELECTRODE, 1, EvolutionItem.LEAF_STONE, null, SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.HISUI_QWILFISH]: [
-    new SpeciesEvolution(Species.OVERQWIL, 28, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.BARB_BARRAGE).length > 0), SpeciesWildEvolutionDelay.LONG)
+    new SpeciesEvolution(Species.OVERQWIL, 28, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.BARB_BARRAGE).length > 0), SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.HISUI_SNEASEL]: [
     new SpeciesEvolution(Species.SNEASLER, 1, null, new SpeciesEvolutionCondition(p => p.scene.arena.getTimeOfDay() === TimeOfDay.DAY /* Razor claw at day*/), SpeciesWildEvolutionDelay.LONG)
@@ -1485,7 +1485,7 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesFormEvolution(Species.SINISTCHA, "artisan", "masterpiece", 1, EvolutionItem.MASTERPIECE_TEACUP, null, SpeciesWildEvolutionDelay.LONG)
   ],
   [Species.DIPPLIN]: [
-    new SpeciesEvolution(Species.HYDRAPPLE, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.DRAGON_CHEER).length > 0), SpeciesWildEvolutionDelay.VERY_LONG)
+    new SpeciesEvolution(Species.HYDRAPPLE, 1, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.DRAGON_CHEER).length > 0), SpeciesWildEvolutionDelay.VERY_LONG)
   ],
   [Species.KADABRA]: [
     new SpeciesEvolution(Species.ALAKAZAM, 1, EvolutionItem.LINKING_CORD, null, SpeciesWildEvolutionDelay.VERY_LONG)
@@ -1501,7 +1501,7 @@ export const pokemonEvolutions: PokemonEvolutions = {
   ],
   [Species.ONIX]: [
     new SpeciesEvolution(Species.STEELIX, 1, EvolutionItem.LINKING_CORD, new SpeciesEvolutionCondition(
-      p => p.moveset.filter(m => m.getMove().type === Type.STEEL).length > 0),
+      p => p.moveset.filter(m => m?.getMove().type === Type.STEEL).length > 0),
     SpeciesWildEvolutionDelay.VERY_LONG)
   ],
   [Species.RHYDON]: [
@@ -1512,7 +1512,7 @@ export const pokemonEvolutions: PokemonEvolutions = {
   ],
   [Species.SCYTHER]: [
     new SpeciesEvolution(Species.SCIZOR, 1, EvolutionItem.LINKING_CORD, new SpeciesEvolutionCondition(
-      p => p.moveset.filter(m => m.getMove().type === Type.STEEL).length > 0),
+      p => p.moveset.filter(m => m?.getMove().type === Type.STEEL).length > 0),
     SpeciesWildEvolutionDelay.VERY_LONG),
     new SpeciesEvolution(Species.KLEAVOR, 1, EvolutionItem.BLACK_AUGURITE, null, SpeciesWildEvolutionDelay.VERY_LONG)
   ],
@@ -1566,7 +1566,7 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesEvolution(Species.ALOLA_GOLEM, 1, EvolutionItem.LINKING_CORD, null, SpeciesWildEvolutionDelay.VERY_LONG)
   ],
   [Species.PRIMEAPE]: [
-    new SpeciesEvolution(Species.ANNIHILAPE, 35, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m.moveId === Moves.RAGE_FIST).length > 0), SpeciesWildEvolutionDelay.VERY_LONG)
+    new SpeciesEvolution(Species.ANNIHILAPE, 35, null, new SpeciesEvolutionCondition(p => p.moveset.filter(m => m?.moveId === Moves.RAGE_FIST).length > 0), SpeciesWildEvolutionDelay.VERY_LONG)
   ],
   [Species.GOLBAT]: [
     new SpeciesEvolution(Species.CROBAT, 1, null, new SpeciesFriendshipEvolutionCondition(110), SpeciesWildEvolutionDelay.VERY_LONG)
diff --git a/src/data/pokemon-forms.ts b/src/data/pokemon-forms.ts
index 7e29ea994e9..a55b9186839 100644
--- a/src/data/pokemon-forms.ts
+++ b/src/data/pokemon-forms.ts
@@ -181,7 +181,7 @@ export class SpeciesFormChange {
     return true;
   }
 
-  findTrigger(triggerType: Constructor<SpeciesFormChangeTrigger>): SpeciesFormChangeTrigger {
+  findTrigger(triggerType: Constructor<SpeciesFormChangeTrigger>): SpeciesFormChangeTrigger | null {
     if (!this.trigger.hasTriggerType(triggerType)) {
       return null;
     }
@@ -189,7 +189,7 @@ export class SpeciesFormChange {
     const trigger = this.trigger;
 
     if (trigger instanceof SpeciesFormChangeCompoundTrigger) {
-      return trigger.triggers.find(t => t.hasTriggerType(triggerType));
+      return trigger.triggers.find(t => t.hasTriggerType(triggerType))!; // TODO: is this bang correct?
     }
 
     return trigger;
@@ -198,11 +198,11 @@ export class SpeciesFormChange {
 
 export class SpeciesFormChangeCondition {
   public predicate: SpeciesFormChangeConditionPredicate;
-  public enforceFunc: SpeciesFormChangeConditionEnforceFunc;
+  public enforceFunc: SpeciesFormChangeConditionEnforceFunc | null;
 
   constructor(predicate: SpeciesFormChangeConditionPredicate, enforceFunc?: SpeciesFormChangeConditionEnforceFunc) {
     this.predicate = predicate;
-    this.enforceFunc = enforceFunc;
+    this.enforceFunc = enforceFunc!; // TODO: is this bang correct?
   }
 }
 
@@ -314,7 +314,7 @@ export class SpeciesFormChangeMoveLearnedTrigger extends SpeciesFormChangeTrigge
   }
 
   canChange(pokemon: Pokemon): boolean {
-    return (!!pokemon.moveset.filter(m => m.moveId === this.move).length) === this.known;
+    return (!!pokemon.moveset.filter(m => m?.moveId === this.move).length) === this.known;
   }
 }
 
@@ -332,7 +332,7 @@ export abstract class SpeciesFormChangeMoveTrigger extends SpeciesFormChangeTrig
 export class SpeciesFormChangePreMoveTrigger extends SpeciesFormChangeMoveTrigger {
   canChange(pokemon: Pokemon): boolean {
     const command = pokemon.scene.currentBattle.turnCommands[pokemon.getBattlerIndex()];
-    return command?.move && this.movePredicate(command.move.move) === this.used;
+    return !!command?.move && this.movePredicate(command.move.move) === this.used;
   }
 }
 
diff --git a/src/data/pokemon-species.ts b/src/data/pokemon-species.ts
index fa6587145ad..837cad4a0df 100644
--- a/src/data/pokemon-species.ts
+++ b/src/data/pokemon-species.ts
@@ -28,21 +28,21 @@ export enum Region {
   PALDEA
 }
 
-export function getPokemonSpecies(species: Species): PokemonSpecies {
+export function getPokemonSpecies(species: Species | Species[]): PokemonSpecies {
   // If a special pool (named trainers) is used here it CAN happen that they have a array as species (which means choose one of those two). So we catch that with this code block
   if (Array.isArray(species)) {
     // Pick a random species from the list
     species = species[Math.floor(Math.random() * species.length)];
   }
   if (species >= 2000) {
-    return allSpecies.find(s => s.speciesId === species);
+    return allSpecies.find(s => s.speciesId === species)!; // TODO: is this bang correct?
   }
   return allSpecies[species - 1];
 }
 
 export function getPokemonSpeciesForm(species: Species, formIndex: integer): PokemonSpeciesForm {
   const retSpecies: PokemonSpecies = species >= 2000
-    ? allSpecies.find(s => s.speciesId === species)
+    ? allSpecies.find(s => s.speciesId === species)! // TODO: is the bang correct?
     : allSpecies[species - 1];
   if (formIndex < retSpecies.forms?.length) {
     return retSpecies.forms[formIndex];
@@ -97,7 +97,7 @@ export function getFusedSpeciesName(speciesAName: string, speciesBName: string):
           fragB = fragB.slice(1);
         } else {
           const newCharMatch = new RegExp(`[^${lastCharA}]`).exec(fragB);
-          if (newCharMatch?.index > 0) {
+          if (newCharMatch?.index !== undefined && newCharMatch.index > 0) {
             fragB = fragB.slice(newCharMatch.index);
           }
         }
@@ -125,7 +125,7 @@ export abstract class PokemonSpeciesForm {
   public formIndex: integer;
   public generation: integer;
   public type1: Type;
-  public type2: Type;
+  public type2: Type | null;
   public height: number;
   public weight: number;
   public ability1: Abilities;
@@ -139,7 +139,7 @@ export abstract class PokemonSpeciesForm {
   public genderDiffs: boolean;
   public isStarterSelectable: boolean;
 
-  constructor(type1: Type, type2: Type, height: number, weight: number, ability1: Abilities, ability2: Abilities, abilityHidden: Abilities,
+  constructor(type1: Type, type2: Type | null, height: number, weight: number, ability1: Abilities, ability2: Abilities, abilityHidden: Abilities,
     baseTotal: integer, baseHp: integer, baseAtk: integer, baseDef: integer, baseSpatk: integer, baseSpdef: integer, baseSpd: integer,
     catchRate: integer, baseFriendship: integer, baseExp: integer, genderDiffs: boolean, isStarterSelectable: boolean) {
     this.type1 = type1;
@@ -267,7 +267,7 @@ export abstract class PokemonSpeciesForm {
     return `${/_[1-3]$/.test(spriteId) ? "variant/" : ""}${spriteId}`;
   }
 
-  getSpriteId(female: boolean, formIndex?: integer, shiny?: boolean, variant?: integer, back?: boolean): string {
+  getSpriteId(female: boolean, formIndex?: integer, shiny?: boolean, variant: integer = 0, back?: boolean): string {
     if (formIndex === undefined || this instanceof PokemonForm) {
       formIndex = this.formIndex;
     }
@@ -281,7 +281,7 @@ export abstract class PokemonSpeciesForm {
     `${back ? "back__" : ""}${baseSpriteKey}`.split("__").map(p => config ? config = config[p] : null);
     const variantSet = config as VariantSet;
 
-    return `${back ? "back__" : ""}${shiny && (!variantSet || (!variant && !variantSet[variant || 0])) ? "shiny__" : ""}${baseSpriteKey}${shiny && variantSet && variantSet[variant || 0] === 2 ? `_${variant + 1}` : ""}`;
+    return `${back ? "back__" : ""}${shiny && (!variantSet || (!variant && !variantSet[variant || 0])) ? "shiny__" : ""}${baseSpriteKey}${shiny && variantSet && variantSet[variant] === 2 ? `_${variant + 1}` : ""}`;
   }
 
   getSpriteKey(female: boolean, formIndex?: integer, shiny?: boolean, variant?: integer): string {
@@ -297,10 +297,10 @@ export abstract class PokemonSpeciesForm {
    * @returns species id if no additional forms, index with formkey if a pokemon with a form
    */
   getVariantDataIndex(formIndex?: integer) {
-    let formkey = null;
-    let variantDataIndex: integer|string = this.speciesId;
+    let formkey: string | null = null;
+    let variantDataIndex: integer | string = this.speciesId;
     const species = getPokemonSpecies(this.speciesId);
-    if (species.forms.length > 0) {
+    if (species.forms.length > 0 && formIndex !== undefined) {
       formkey = species.forms[formIndex]?.formSpriteKey;
       if (formkey) {
         variantDataIndex = `${this.speciesId}-${formkey}`;
@@ -311,7 +311,7 @@ export abstract class PokemonSpeciesForm {
 
   getIconAtlasKey(formIndex?: integer, shiny?: boolean, variant?: integer): string {
     const variantDataIndex = this.getVariantDataIndex(formIndex);
-    const isVariant = shiny && variantData[variantDataIndex] && variantData[variantDataIndex][variant];
+    const isVariant = shiny && variantData[variantDataIndex] && (variant !== undefined && variantData[variantDataIndex][variant]);
     return `pokemon_icons_${this.generation}${isVariant ? "v" : ""}`;
   }
 
@@ -324,7 +324,7 @@ export abstract class PokemonSpeciesForm {
 
     let ret = this.speciesId.toString();
 
-    const isVariant = shiny && variantData[variantDataIndex] && variantData[variantDataIndex][variant];
+    const isVariant = shiny && variantData[variantDataIndex] && (variant !== undefined && variantData[variantDataIndex][variant]);
 
     if (shiny && !isVariant) {
       ret += "s";
@@ -382,7 +382,7 @@ export abstract class PokemonSpeciesForm {
     let ret = speciesId.toString();
     const forms = getPokemonSpecies(speciesId).forms;
     if (forms.length) {
-      if (formIndex >= forms.length) {
+      if (formIndex !== undefined && formIndex >= forms.length) {
         console.warn(`Attempted accessing form with index ${formIndex} of species ${getPokemonSpecies(speciesId).getName()} with only ${forms.length || 0} forms`);
         formIndex = Math.min(formIndex, forms.length - 1);
       }
@@ -478,7 +478,7 @@ export abstract class PokemonSpeciesForm {
         let config = variantData;
         spritePath.split("/").map(p => config ? config = config[p] : null);
         const variantSet = config as VariantSet;
-        if (variantSet && variantSet[variant] === 1) {
+        if (variantSet && (variant !== undefined && variantSet[variant] === 1)) {
           const populateVariantColors = (key: string): Promise<void> => {
             return new Promise(resolve => {
               if (variantColorCache.hasOwnProperty(key)) {
@@ -507,7 +507,7 @@ export abstract class PokemonSpeciesForm {
 
   cry(scene: BattleScene, soundConfig?: Phaser.Types.Sound.SoundConfig, ignorePlay?: boolean): AnySound {
     const cryKey = this.getCryKey(this.formIndex);
-    let cry = scene.sound.get(cryKey) as AnySound;
+    let cry: AnySound | null = scene.sound.get(cryKey) as AnySound;
     if (cry?.pendingRemove) {
       cry = null;
     }
@@ -532,30 +532,32 @@ export abstract class PokemonSpeciesForm {
     const frame = sourceFrame;
     canvas.width = frame.width;
     canvas.height = frame.height;
-    context.drawImage(sourceImage, frame.cutX, frame.cutY, frame.width, frame.height, 0, 0, frame.width, frame.height);
-    const imageData = context.getImageData(frame.cutX, frame.cutY, frame.width, frame.height);
-    const pixelData = imageData.data;
+    context?.drawImage(sourceImage, frame.cutX, frame.cutY, frame.width, frame.height, 0, 0, frame.width, frame.height);
+    const imageData = context?.getImageData(frame.cutX, frame.cutY, frame.width, frame.height);
+    const pixelData = imageData?.data;
+    const pixelColors: number[] = [];
 
-    for (let i = 0; i < pixelData.length; i += 4) {
-      if (pixelData[i + 3]) {
-        const pixel = pixelData.slice(i, i + 4);
-        const [ r, g, b, a ] = pixel;
-        if (!spriteColors.find(c => c[0] === r && c[1] === g && c[2] === b)) {
-          spriteColors.push([ r, g, b, a ]);
+    if (pixelData?.length !== undefined) {
+      for (let i = 0; i < pixelData.length; i += 4) {
+        if (pixelData[i + 3]) {
+          const pixel = pixelData.slice(i, i + 4);
+          const [ r, g, b, a ] = pixel;
+          if (!spriteColors.find(c => c[0] === r && c[1] === g && c[2] === b)) {
+            spriteColors.push([ r, g, b, a ]);
+          }
         }
       }
-    }
 
-    const pixelColors = [];
-    for (let i = 0; i < pixelData.length; i += 4) {
-      const total = pixelData.slice(i, i + 3).reduce((total: integer, value: integer) => total + value, 0);
-      if (!total) {
-        continue;
+      for (let i = 0; i < pixelData.length; i += 4) {
+        const total = pixelData.slice(i, i + 3).reduce((total: integer, value: integer) => total + value, 0);
+        if (!total) {
+          continue;
+        }
+        pixelColors.push(argbFromRgba({ r: pixelData[i], g: pixelData[i + 1], b: pixelData[i + 2], a: pixelData[i + 3] }));
       }
-      pixelColors.push(argbFromRgba({ r: pixelData[i], g: pixelData[i + 1], b: pixelData[i + 2], a: pixelData[i + 3] }));
     }
 
-    let paletteColors: Map<number, number>;
+    let paletteColors: Map<number, number> = new Map();
 
     const originalRandom = Math.random;
     Math.random = () => Phaser.Math.RND.realInRange(0, 1);
@@ -577,15 +579,15 @@ export default class PokemonSpecies extends PokemonSpeciesForm implements Locali
   public mythical: boolean;
   public species: string;
   public growthRate: GrowthRate;
-  public malePercent: number;
+  public malePercent: number | null;
   public genderDiffs: boolean;
   public canChangeForm: boolean;
   public forms: PokemonForm[];
 
   constructor(id: Species, generation: integer, subLegendary: boolean, legendary: boolean, mythical: boolean, species: string,
-    type1: Type, type2: Type, height: number, weight: number, ability1: Abilities, ability2: Abilities, abilityHidden: Abilities,
+    type1: Type, type2: Type | null, height: number, weight: number, ability1: Abilities, ability2: Abilities, abilityHidden: Abilities,
     baseTotal: integer, baseHp: integer, baseAtk: integer, baseDef: integer, baseSpatk: integer, baseSpdef: integer, baseSpd: integer,
-    catchRate: integer, baseFriendship: integer, baseExp: integer, growthRate: GrowthRate, malePercent: number,
+    catchRate: integer, baseFriendship: integer, baseExp: integer, growthRate: GrowthRate, malePercent: number | null,
     genderDiffs: boolean, canChangeForm?: boolean, ...forms: PokemonForm[]) {
     super(type1, type2, height, weight, ability1, ability2, abilityHidden, baseTotal, baseHp, baseAtk, baseDef, baseSpatk, baseSpdef, baseSpd,
       catchRate, baseFriendship, baseExp, genderDiffs, false);
@@ -614,7 +616,7 @@ export default class PokemonSpecies extends PokemonSpeciesForm implements Locali
   getName(formIndex?: integer): string {
     if (formIndex !== undefined && this.forms.length) {
       const form = this.forms[formIndex];
-      let key: string;
+      let key: string | null;
       switch (form.formKey) {
       case SpeciesFormKey.MEGA:
       case SpeciesFormKey.PRIMAL:
@@ -626,6 +628,8 @@ export default class PokemonSpecies extends PokemonSpeciesForm implements Locali
       default:
         if (form.formKey.indexOf(SpeciesFormKey.GIGANTAMAX) > -1) {
           key = "gigantamax";
+        } else {
+          key = null;
         }
       }
 
@@ -713,11 +717,11 @@ export default class PokemonSpecies extends PokemonSpeciesForm implements Locali
             evolutionChance = Math.min(minChance + easeInFunc(Math.min(level - ev.level, maxLevelDiff) / maxLevelDiff) * (1 - minChance), 1);
           }
         } else {
-          const preferredMinLevel = Math.max((ev.level - 1) + ev.wildDelay * this.getStrengthLevelDiff(strength), 1);
+          const preferredMinLevel = Math.max((ev.level - 1) + (ev.wildDelay!) * this.getStrengthLevelDiff(strength), 1); // TODO: is the bang correct?
           let evolutionLevel = Math.max(ev.level > 1 ? ev.level : Math.floor(preferredMinLevel / 2), 1);
 
           if (ev.level <= 1 && pokemonPrevolutions.hasOwnProperty(this.speciesId)) {
-            const prevolutionLevel = pokemonEvolutions[pokemonPrevolutions[this.speciesId]].find(ev => ev.speciesId === this.speciesId).level;
+            const prevolutionLevel = pokemonEvolutions[pokemonPrevolutions[this.speciesId]].find(ev => ev.speciesId === this.speciesId)!.level; // TODO: is the bang correct?
             if (prevolutionLevel > 1) {
               evolutionLevel = prevolutionLevel;
             }
@@ -750,15 +754,15 @@ export default class PokemonSpecies extends PokemonSpeciesForm implements Locali
 
     for (const weight of evolutionPool.keys()) {
       if (randValue < weight) {
-        return getPokemonSpecies(evolutionPool.get(weight)).getSpeciesForLevel(level, true, forTrainer, strength);
+        return getPokemonSpecies(evolutionPool.get(weight)!).getSpeciesForLevel(level, true, forTrainer, strength); // TODO: is the bang correct?
       }
     }
 
     return this.speciesId;
   }
 
-  getEvolutionLevels() {
-    const evolutionLevels = [];
+  getEvolutionLevels(): [Species, integer][] {
+    const evolutionLevels: [Species, integer][] = [];
 
     //console.log(Species[this.speciesId], pokemonEvolutions[this.speciesId])
 
@@ -778,8 +782,8 @@ export default class PokemonSpecies extends PokemonSpeciesForm implements Locali
     return evolutionLevels;
   }
 
-  getPrevolutionLevels() {
-    const prevolutionLevels = [];
+  getPrevolutionLevels(): [Species, integer][] {
+    const prevolutionLevels: [Species, integer][] = [];
 
     const allEvolvingPokemon = Object.keys(pokemonEvolutions);
     for (const p of allEvolvingPokemon) {
@@ -801,18 +805,18 @@ export default class PokemonSpecies extends PokemonSpeciesForm implements Locali
 
   // This could definitely be written better and more accurate to the getSpeciesForLevel logic, but it is only for generating movesets for evolved Pokemon
   getSimulatedEvolutionChain(currentLevel: integer, forTrainer: boolean = false, isBoss: boolean = false, player: boolean = false): [Species, integer][] {
-    const ret = [];
+    const ret: [Species, integer][] = [];
     if (pokemonPrevolutions.hasOwnProperty(this.speciesId)) {
       const prevolutionLevels = this.getPrevolutionLevels().reverse();
       const levelDiff = player ? 0 : forTrainer || isBoss ? forTrainer && isBoss ? 2.5 : 5 : 10;
       ret.push([ prevolutionLevels[0][0], 1 ]);
       for (let l = 1; l < prevolutionLevels.length; l++) {
         const evolution = pokemonEvolutions[prevolutionLevels[l - 1][0]].find(e => e.speciesId === prevolutionLevels[l][0]);
-        ret.push([ prevolutionLevels[l][0], Math.min(Math.max(evolution.level + Math.round(Utils.randSeedGauss(0.5, 1 + levelDiff * 0.2) * Math.max(evolution.wildDelay, 0.5) * 5) - 1, 2, evolution.level), currentLevel - 1) ]);
+        ret.push([ prevolutionLevels[l][0], Math.min(Math.max((evolution?.level!) + Math.round(Utils.randSeedGauss(0.5, 1 + levelDiff * 0.2) * Math.max((evolution?.wildDelay!), 0.5) * 5) - 1, 2, (evolution?.level!)), currentLevel - 1) ]); // TODO: are those bangs correct?
       }
       const lastPrevolutionLevel = ret[prevolutionLevels.length - 1][1];
       const evolution = pokemonEvolutions[prevolutionLevels[prevolutionLevels.length - 1][0]].find(e => e.speciesId === this.speciesId);
-      ret.push([ this.speciesId, Math.min(Math.max(lastPrevolutionLevel + Math.round(Utils.randSeedGauss(0.5, 1 + levelDiff * 0.2) * Math.max(evolution.wildDelay, 0.5) * 5), lastPrevolutionLevel + 1, evolution.level), currentLevel) ]);
+      ret.push([ this.speciesId, Math.min(Math.max(lastPrevolutionLevel + Math.round(Utils.randSeedGauss(0.5, 1 + levelDiff * 0.2) * Math.max((evolution?.wildDelay!), 0.5) * 5), lastPrevolutionLevel + 1, (evolution?.level!)), currentLevel) ]); // TODO: are those bangs correct?
     } else {
       ret.push([ this.speciesId, 1 ]);
     }
@@ -853,7 +857,7 @@ export default class PokemonSpecies extends PokemonSpeciesForm implements Locali
   }
 
   getFormSpriteKey(formIndex?: integer) {
-    if (this.forms.length && formIndex >= this.forms.length) {
+    if (this.forms.length && (formIndex !== undefined && formIndex >= this.forms.length)) {
       console.warn(`Attempted accessing form with index ${formIndex} of species ${this.getName()} with only ${this.forms.length || 0} forms`);
       formIndex = Math.min(formIndex, this.forms.length - 1);
     }
@@ -866,14 +870,14 @@ export default class PokemonSpecies extends PokemonSpeciesForm implements Locali
 export class PokemonForm extends PokemonSpeciesForm {
   public formName: string;
   public formKey: string;
-  public formSpriteKey: string;
+  public formSpriteKey: string | null;
 
   // This is a collection of form keys that have in-run form changes, but should still be separately selectable from the start screen
   private starterSelectableKeys: string[] = ["10", "50", "10-pc", "50-pc", "red", "orange", "yellow", "green", "blue", "indigo", "violet"];
 
-  constructor(formName: string, formKey: string, type1: Type, type2: Type, height: number, weight: number, ability1: Abilities, ability2: Abilities, abilityHidden: Abilities,
+  constructor(formName: string, formKey: string, type1: Type, type2: Type | null, height: number, weight: number, ability1: Abilities, ability2: Abilities, abilityHidden: Abilities,
     baseTotal: integer, baseHp: integer, baseAtk: integer, baseDef: integer, baseSpatk: integer, baseSpdef: integer, baseSpd: integer,
-    catchRate: integer, baseFriendship: integer, baseExp: integer, genderDiffs?: boolean, formSpriteKey?: string, isStarterSelectable?: boolean, ) {
+    catchRate: integer, baseFriendship: integer, baseExp: integer, genderDiffs?: boolean, formSpriteKey?: string | null, isStarterSelectable?: boolean, ) {
     super(type1, type2, height, weight, ability1, ability2, abilityHidden, baseTotal, baseHp, baseAtk, baseDef, baseSpatk, baseSpdef, baseSpd,
       catchRate, baseFriendship, baseExp, !!genderDiffs, (!!isStarterSelectable || !formKey));
     this.formName = formName;
diff --git a/src/data/status-effect.ts b/src/data/status-effect.ts
index 65caf58ccb9..828c52cae13 100644
--- a/src/data/status-effect.ts
+++ b/src/data/status-effect.ts
@@ -7,12 +7,12 @@ export { StatusEffect };
 export class Status {
   public effect: StatusEffect;
   public turnCount: integer;
-  public cureTurn: integer;
+  public cureTurn: integer | null;
 
   constructor(effect: StatusEffect, turnCount: integer = 0, cureTurn?: integer) {
     this.effect = effect;
     this.turnCount = turnCount === undefined ? 0 : turnCount;
-    this.cureTurn = cureTurn;
+    this.cureTurn = cureTurn!; // TODO: is this bang correct?
   }
 
   incrementTurn(): void {
@@ -24,7 +24,7 @@ export class Status {
   }
 }
 
-function getStatusEffectMessageKey(statusEffect: StatusEffect): string {
+function getStatusEffectMessageKey(statusEffect: StatusEffect | undefined): string {
   switch (statusEffect) {
   case StatusEffect.POISON:
     return "statusEffect:poison";
@@ -43,7 +43,7 @@ function getStatusEffectMessageKey(statusEffect: StatusEffect): string {
   }
 }
 
-export function getStatusEffectObtainText(statusEffect: StatusEffect, pokemonNameWithAffix: string, sourceText?: string): string {
+export function getStatusEffectObtainText(statusEffect: StatusEffect | undefined, pokemonNameWithAffix: string, sourceText?: string): string {
   if (!sourceText) {
     const i18nKey = `${getStatusEffectMessageKey(statusEffect)}.obtain`as ParseKeys;
     return i18next.t(i18nKey, { pokemonNameWithAffix: pokemonNameWithAffix });
diff --git a/src/data/trainer-config.ts b/src/data/trainer-config.ts
index 87d1901eb01..5f47ce42a62 100644
--- a/src/data/trainer-config.ts
+++ b/src/data/trainer-config.ts
@@ -288,7 +288,7 @@ export class TrainerConfig {
      * @param trainerTypeToDeriveFrom - The trainer type to derive from. (If null, the this.trainerType property will be used.)
      * @returns {TrainerType} - The derived trainer type.
      */
-  getDerivedType(trainerTypeToDeriveFrom: TrainerType = null): TrainerType {
+  getDerivedType(trainerTypeToDeriveFrom: TrainerType | null = null): TrainerType {
     let trainerType = trainerTypeToDeriveFrom ? trainerTypeToDeriveFrom : this.trainerType;
     switch (trainerType) {
     case TrainerType.RIVAL_2:
@@ -361,7 +361,7 @@ export class TrainerConfig {
       this.nameFemale = i18next.t("trainerNames:rival_female");
     } else {
       // Otherwise, assign the provided female name.
-      this.nameFemale = nameFemale;
+      this.nameFemale = nameFemale!; // TODO: is this bang correct?
     }
 
     // Indicate that this trainer configuration includes genders.
@@ -587,6 +587,9 @@ export class TrainerConfig {
       };
     }
     }
+
+    console.warn(`Evil team admin for ${team} not found. Returning empty species pools.`);
+    return [];
   }
 
   /**
@@ -715,7 +718,7 @@ export class TrainerConfig {
     this.setVictoryBgm("victory_gym");
     this.setGenModifiersFunc(party => {
       const waveIndex = party[0].scene.currentBattle.waveIndex;
-      return getRandomTeraModifiers(party, waveIndex >= 100 ? 1 : 0, specialtyTypes.length ? specialtyTypes : null);
+      return getRandomTeraModifiers(party, waveIndex >= 100 ? 1 : 0, specialtyTypes.length ? specialtyTypes : undefined);
     });
 
     return this;
@@ -749,7 +752,7 @@ export class TrainerConfig {
 
     // Set species filter and specialty types if provided, otherwise filter by base total.
     if (specialtyTypes.length) {
-      this.setSpeciesFilter(p => specialtyTypes.find(t => p.isOfType(t)) && p.baseTotal >= 450);
+      this.setSpeciesFilter(p => specialtyTypes.some(t => p.isOfType(t)) && p.baseTotal >= 450);
       this.setSpecialtyTypes(...specialtyTypes);
     } else {
       this.setSpeciesFilter(p => p.baseTotal >= 450);
@@ -772,7 +775,7 @@ export class TrainerConfig {
     this.setHasVoucher(true);
     this.setBattleBgm("battle_unova_elite");
     this.setVictoryBgm("victory_gym");
-    this.setGenModifiersFunc(party => getRandomTeraModifiers(party, 2, specialtyTypes.length ? specialtyTypes : null));
+    this.setGenModifiersFunc(party => getRandomTeraModifiers(party, 2, specialtyTypes.length ? specialtyTypes : undefined));
 
     return this;
   }
@@ -897,7 +900,7 @@ export class TrainerConfig {
             start: 1,
             end: 128
           })
-          : null;
+          : "";
         console.warn = originalWarn;
         if (!(scene.anims.exists(trainerKey))) {
           scene.anims.create({
@@ -983,7 +986,7 @@ function getRandomTeraModifiers(party: EnemyPokemon[], count: integer, types?: T
   for (let t = 0; t < Math.min(count, party.length); t++) {
     const randomIndex = Utils.randSeedItem(partyMemberIndexes);
     partyMemberIndexes.splice(partyMemberIndexes.indexOf(randomIndex), 1);
-    ret.push(modifierTypes.TERA_SHARD().generateType(null, [Utils.randSeedItem(types ? types : party[randomIndex].getTypes())]).withIdFromFunc(modifierTypes.TERA_SHARD).newModifier(party[randomIndex]) as PersistentModifier);
+    ret.push(modifierTypes.TERA_SHARD().generateType([], [Utils.randSeedItem(types ? types : party[randomIndex].getTypes())])!.withIdFromFunc(modifierTypes.TERA_SHARD).newModifier(party[randomIndex]) as PersistentModifier); // TODO: is the bang correct?
   }
   return ret;
 }
@@ -1594,7 +1597,7 @@ export const trainerConfigs: TrainerConfigs = {
     .setSpeciesFilter(species => species.baseTotal >= 540)
     .setGenModifiersFunc(party => {
       const starter = party[0];
-      return [modifierTypes.TERA_SHARD().generateType(null, [starter.species.type1]).withIdFromFunc(modifierTypes.TERA_SHARD).newModifier(starter) as PersistentModifier];
+      return [modifierTypes.TERA_SHARD().generateType([], [starter.species.type1])!.withIdFromFunc(modifierTypes.TERA_SHARD).newModifier(starter) as PersistentModifier]; // TODO: is the bang correct?
     }),
   [TrainerType.RIVAL_5]: new TrainerConfig(++t).setName("Finn").setHasGenders("Ivy").setHasCharSprite().setTitle("Rival").setBoss().setStaticParty().setMoneyMultiplier(2.25).setEncounterBgm(TrainerType.RIVAL).setBattleBgm("battle_rival_3").setMixedBattleBgm("battle_rival_3").setPartyTemplates(trainerPartyTemplates.RIVAL_5)
     .setPartyMemberFunc(0, getRandomPartyMemberFunc([Species.VENUSAUR, Species.CHARIZARD, Species.BLASTOISE, Species.MEGANIUM, Species.TYPHLOSION, Species.FERALIGATR, Species.SCEPTILE, Species.BLAZIKEN, Species.SWAMPERT, Species.TORTERRA, Species.INFERNAPE, Species.EMPOLEON, Species.SERPERIOR, Species.EMBOAR, Species.SAMUROTT, Species.CHESNAUGHT, Species.DELPHOX, Species.GRENINJA, Species.DECIDUEYE, Species.INCINEROAR, Species.PRIMARINA, Species.RILLABOOM, Species.CINDERACE, Species.INTELEON, Species.MEOWSCARADA, Species.SKELEDIRGE, Species.QUAQUAVAL], TrainerSlot.TRAINER, true,
@@ -1610,7 +1613,7 @@ export const trainerConfigs: TrainerConfigs = {
     }))
     .setGenModifiersFunc(party => {
       const starter = party[0];
-      return [modifierTypes.TERA_SHARD().generateType(null, [starter.species.type1]).withIdFromFunc(modifierTypes.TERA_SHARD).newModifier(starter) as PersistentModifier];
+      return [modifierTypes.TERA_SHARD().generateType([], [starter.species.type1])!.withIdFromFunc(modifierTypes.TERA_SHARD).newModifier(starter) as PersistentModifier]; //TODO: is the bang correct?
     }),
   [TrainerType.RIVAL_6]: new TrainerConfig(++t).setName("Finn").setHasGenders("Ivy").setHasCharSprite().setTitle("Rival").setBoss().setStaticParty().setMoneyMultiplier(3).setEncounterBgm("final").setBattleBgm("battle_rival_3").setMixedBattleBgm("battle_rival_3").setPartyTemplates(trainerPartyTemplates.RIVAL_6)
     .setPartyMemberFunc(0, getRandomPartyMemberFunc([Species.VENUSAUR, Species.CHARIZARD, Species.BLASTOISE, Species.MEGANIUM, Species.TYPHLOSION, Species.FERALIGATR, Species.SCEPTILE, Species.BLAZIKEN, Species.SWAMPERT, Species.TORTERRA, Species.INFERNAPE, Species.EMPOLEON, Species.SERPERIOR, Species.EMBOAR, Species.SAMUROTT, Species.CHESNAUGHT, Species.DELPHOX, Species.GRENINJA, Species.DECIDUEYE, Species.INCINEROAR, Species.PRIMARINA, Species.RILLABOOM, Species.CINDERACE, Species.INTELEON, Species.MEOWSCARADA, Species.SKELEDIRGE, Species.QUAQUAVAL], TrainerSlot.TRAINER, true,
@@ -1636,7 +1639,7 @@ export const trainerConfigs: TrainerConfigs = {
     }))
     .setGenModifiersFunc(party => {
       const starter = party[0];
-      return [modifierTypes.TERA_SHARD().generateType(null, [starter.species.type1]).withIdFromFunc(modifierTypes.TERA_SHARD).newModifier(starter) as PersistentModifier];
+      return [modifierTypes.TERA_SHARD().generateType([], [starter.species.type1])!.withIdFromFunc(modifierTypes.TERA_SHARD).newModifier(starter) as PersistentModifier]; // TODO: is the bang correct?
     }),
 
   [TrainerType.ROCKET_BOSS_GIOVANNI_1]: new TrainerConfig(t = TrainerType.ROCKET_BOSS_GIOVANNI_1).setName("Giovanni").initForEvilTeamLeader("Rocket Boss", []).setMixedBattleBgm("battle_rocket_boss").setVictoryBgm("victory_team_plasma")
diff --git a/src/data/trainer-names.ts b/src/data/trainer-names.ts
index b986378ee47..447f9fd4284 100644
--- a/src/data/trainer-names.ts
+++ b/src/data/trainer-names.ts
@@ -3,7 +3,7 @@ import * as Utils from "../utils";
 
 class TrainerNameConfig {
   public urls: string[];
-  public femaleUrls: string[];
+  public femaleUrls: string[] | null;
 
   constructor(type: TrainerType, ...urls: string[]) {
     this.urls = urls.length ? urls : [ Utils.toReadableString(TrainerType[type]).replace(/ /g, "_") ];
@@ -136,8 +136,11 @@ function fetchAndPopulateTrainerNames(url: string, parser: DOMParser, trainerNam
       .then(html => {
         console.log(url);
         const htmlDoc = parser.parseFromString(html, "text/html");
-        const trainerListHeader = htmlDoc.querySelector("#Trainer_list").parentElement;
-        const elements = [...trainerListHeader.parentElement.childNodes];
+        const trainerListHeader = htmlDoc.querySelector("#Trainer_list")?.parentElement;
+        if (!trainerListHeader) {
+          return [];
+        }
+        const elements = [...(trainerListHeader?.parentElement?.childNodes ?? [])];
         const startChildIndex = elements.indexOf(trainerListHeader);
         const endChildIndex = elements.findIndex(h => h.nodeName === "H2" && elements.indexOf(h) > startChildIndex);
         const tables = elements.filter(t => {
@@ -152,6 +155,9 @@ function fetchAndPopulateTrainerNames(url: string, parser: DOMParser, trainerNam
           const trainerRows = [...table.querySelectorAll("tr:not(:first-child)")].filter(r => r.children.length === 9);
           for (const row of trainerRows) {
             const nameCell = row.firstElementChild;
+            if (!nameCell) {
+              continue;
+            }
             const content = nameCell.innerHTML;
             if (content.indexOf(" <a ") > -1) {
               const female = /♀/.test(content);
diff --git a/src/data/type.ts b/src/data/type.ts
index 1330eb83f4b..7a9f7f3605e 100644
--- a/src/data/type.ts
+++ b/src/data/type.ts
@@ -499,6 +499,8 @@ export function getTypeDamageMultiplier(attackType: integer, defType: integer):
   case Type.STELLAR:
     return 1;
   }
+
+  return 0;
 }
 
 /**
diff --git a/src/data/weather.ts b/src/data/weather.ts
index 901ad08d164..2421f719e6e 100644
--- a/src/data/weather.ts
+++ b/src/data/weather.ts
@@ -103,7 +103,7 @@ export class Weather {
     const field = scene.getField(true);
 
     for (const pokemon of field) {
-      let suppressWeatherEffectAbAttr = pokemon.getAbility().getAttrs(SuppressWeatherEffectAbAttr)[0];
+      let suppressWeatherEffectAbAttr: SuppressWeatherEffectAbAttr | null  = pokemon.getAbility().getAttrs(SuppressWeatherEffectAbAttr)[0];
       if (!suppressWeatherEffectAbAttr) {
         suppressWeatherEffectAbAttr = pokemon.hasPassive() ? pokemon.getPassiveAbility().getAttrs(SuppressWeatherEffectAbAttr)[0] : null;
       }
@@ -116,7 +116,7 @@ export class Weather {
   }
 }
 
-export function getWeatherStartMessage(weatherType: WeatherType): string {
+export function getWeatherStartMessage(weatherType: WeatherType): string | null {
   switch (weatherType) {
   case WeatherType.SUNNY:
     return i18next.t("weather:sunnyStartMessage");
@@ -141,7 +141,7 @@ export function getWeatherStartMessage(weatherType: WeatherType): string {
   return null;
 }
 
-export function getWeatherLapseMessage(weatherType: WeatherType): string {
+export function getWeatherLapseMessage(weatherType: WeatherType): string | null {
   switch (weatherType) {
   case WeatherType.SUNNY:
     return i18next.t("weather:sunnyLapseMessage");
@@ -166,7 +166,7 @@ export function getWeatherLapseMessage(weatherType: WeatherType): string {
   return null;
 }
 
-export function getWeatherDamageMessage(weatherType: WeatherType, pokemon: Pokemon): string {
+export function getWeatherDamageMessage(weatherType: WeatherType, pokemon: Pokemon): string | null {
   switch (weatherType) {
   case WeatherType.SANDSTORM:
     return i18next.t("weather:sandstormDamageMessage", {pokemonNameWithAffix: getPokemonNameWithAffix(pokemon)});
@@ -177,7 +177,7 @@ export function getWeatherDamageMessage(weatherType: WeatherType, pokemon: Pokem
   return null;
 }
 
-export function getWeatherClearMessage(weatherType: WeatherType): string {
+export function getWeatherClearMessage(weatherType: WeatherType): string | null {
   switch (weatherType) {
   case WeatherType.SUNNY:
     return i18next.t("weather:sunnyClearMessage");
@@ -202,7 +202,7 @@ export function getWeatherClearMessage(weatherType: WeatherType): string {
   return null;
 }
 
-export function getTerrainStartMessage(terrainType: TerrainType): string {
+export function getTerrainStartMessage(terrainType: TerrainType): string | null {
   switch (terrainType) {
   case TerrainType.MISTY:
     return i18next.t("terrain:mistyStartMessage");
@@ -212,10 +212,13 @@ export function getTerrainStartMessage(terrainType: TerrainType): string {
     return i18next.t("terrain:grassyStartMessage");
   case TerrainType.PSYCHIC:
     return i18next.t("terrain:psychicStartMessage");
+  default:
+    console.warn("getTerrainStartMessage not defined. Using default null");
+    return null;
   }
 }
 
-export function getTerrainClearMessage(terrainType: TerrainType): string {
+export function getTerrainClearMessage(terrainType: TerrainType): string | null {
   switch (terrainType) {
   case TerrainType.MISTY:
     return i18next.t("terrain:mistyClearMessage");
@@ -225,6 +228,9 @@ export function getTerrainClearMessage(terrainType: TerrainType): string {
     return i18next.t("terrain:grassyClearMessage");
   case TerrainType.PSYCHIC:
     return i18next.t("terrain:psychicClearMessage");
+  default:
+    console.warn("getTerrainClearMessage not defined. Using default null");
+    return null;
   }
 }
 
diff --git a/src/egg-hatch-phase.ts b/src/egg-hatch-phase.ts
index 3965eae74f6..73c88cbde37 100644
--- a/src/egg-hatch-phase.ts
+++ b/src/egg-hatch-phase.ts
@@ -84,7 +84,7 @@ export class EggHatchPhase extends Phase {
 
       this.scene.gameData.eggs.splice(eggIndex, 1);
 
-      this.scene.fadeOutBgm(null, false);
+      this.scene.fadeOutBgm(undefined, false);
 
       this.eggHatchHandler = this.scene.ui.getHandler() as EggHatchSceneHandler;
 
@@ -234,8 +234,8 @@ export class EggHatchPhase extends Phase {
             ease: "Sine.easeInOut",
             duration: 250,
             onComplete: () => {
-              count++;
-              if (count < repeatCount) {
+              count!++;
+              if (count! < repeatCount!) { // we know they are defined
                 return this.doEggShake(intensity, repeatCount, count).then(() => resolve());
               }
               this.scene.tweens.add({
@@ -347,7 +347,7 @@ export class EggHatchPhase extends Phase {
           this.scene.gameData.updateSpeciesDexIvs(this.pokemon.species.speciesId, this.pokemon.ivs);
           this.scene.gameData.setPokemonCaught(this.pokemon, true, true).then(() => {
             this.scene.gameData.setEggMoveUnlocked(this.pokemon.species, this.eggMoveIndex).then(() => {
-              this.scene.ui.showText(null, 0);
+              this.scene.ui.showText("", 0);
               this.end();
             });
           });
@@ -447,6 +447,6 @@ export class EggHatchPhase extends Phase {
 
     }, this.egg.id, EGG_SEED.toString());
 
-    return ret;
+    return ret!;
   }
 }
diff --git a/src/events/arena.ts b/src/events/arena.ts
index 67b423f3b75..9fbbe572601 100644
--- a/src/events/arena.ts
+++ b/src/events/arena.ts
@@ -81,8 +81,8 @@ export class TagAddedEvent extends ArenaEvent {
 
     this.arenaTagType = arenaTagType;
     this.arenaTagSide = arenaTagSide;
-    this.arenaTagLayers = arenaTagLayers;
-    this.arenaTagMaxLayers = arenaTagMaxLayers;
+    this.arenaTagLayers = arenaTagLayers!; // TODO: is this bang correct?
+    this.arenaTagMaxLayers = arenaTagMaxLayers!; // TODO: is this bang correct?
   }
 }
 /**
diff --git a/src/evolution-phase.ts b/src/evolution-phase.ts
index 7633fbb3fdd..7b50a6368f6 100644
--- a/src/evolution-phase.ts
+++ b/src/evolution-phase.ts
@@ -16,7 +16,7 @@ export class EvolutionPhase extends Phase {
   protected pokemon: PlayerPokemon;
   protected lastLevel: integer;
 
-  private evolution: SpeciesFormEvolution;
+  private evolution: SpeciesFormEvolution | null;
 
   protected evolutionContainer: Phaser.GameObjects.Container;
   protected evolutionBaseBg: Phaser.GameObjects.Image;
@@ -28,7 +28,7 @@ export class EvolutionPhase extends Phase {
   protected pokemonEvoSprite: Phaser.GameObjects.Sprite;
   protected pokemonEvoTintSprite: Phaser.GameObjects.Sprite;
 
-  constructor(scene: BattleScene, pokemon: PlayerPokemon, evolution: SpeciesFormEvolution, lastLevel: integer) {
+  constructor(scene: BattleScene, pokemon: PlayerPokemon, evolution: SpeciesFormEvolution | null, lastLevel: integer) {
     super(scene);
 
     this.pokemon = pokemon;
@@ -53,7 +53,7 @@ export class EvolutionPhase extends Phase {
         return this.end();
       }
 
-      this.scene.fadeOutBgm(null, false);
+      this.scene.fadeOutBgm(undefined, false);
 
       const evolutionHandler = this.scene.ui.getHandler() as EvolutionSceneHandler;
 
@@ -195,7 +195,7 @@ export class EvolutionPhase extends Phase {
                           this.scene.ui.showText(i18next.t("menu:stoppedEvolving", { pokemonName: preName }), null, () => {
                             this.scene.ui.showText(i18next.t("menu:pauseEvolutionsQuestion", { pokemonName: preName }), null, () => {
                               const end = () => {
-                                this.scene.ui.showText(null, 0);
+                                this.scene.ui.showText("", 0);
                                 this.scene.playBgm();
                                 evolvedPokemon.destroy();
                                 this.end();
diff --git a/src/field/arena.ts b/src/field/arena.ts
index cb045cc76ac..923a0a4e286 100644
--- a/src/field/arena.ts
+++ b/src/field/arena.ts
@@ -25,8 +25,8 @@ import { TrainerType } from "#enums/trainer-type";
 export class Arena {
   public scene: BattleScene;
   public biomeType: Biome;
-  public weather: Weather;
-  public terrain: Terrain;
+  public weather: Weather | null;
+  public terrain: Terrain | null;
   public tags: ArenaTag[];
   public bgm: string;
   public ignoreAbilities: boolean;
@@ -121,7 +121,7 @@ export class Arena {
         }
       }
 
-      ret = getPokemonSpecies(species);
+      ret = getPokemonSpecies(species!);
 
       if (ret.subLegendary || ret.legendary || ret.mythical) {
         switch (true) {
@@ -292,7 +292,7 @@ export class Arena {
   trySetWeatherOverride(weather: WeatherType): boolean {
     this.weather = new Weather(weather, 0);
     this.scene.unshiftPhase(new CommonAnimPhase(this.scene, undefined, undefined, CommonAnim.SUNNY + (weather - 1)));
-    this.scene.queueMessage(getWeatherStartMessage(weather));
+    this.scene.queueMessage(getWeatherStartMessage(weather)!); // TODO: is this bang correct?
     return true;
   }
 
@@ -314,13 +314,13 @@ export class Arena {
     const oldWeatherType = this.weather?.weatherType || WeatherType.NONE;
 
     this.weather = weather ? new Weather(weather, hasPokemonSource ? 5 : 0) : null;
-    this.eventTarget.dispatchEvent(new WeatherChangedEvent(oldWeatherType, this.weather?.weatherType, this.weather?.turnsLeft));
+    this.eventTarget.dispatchEvent(new WeatherChangedEvent(oldWeatherType, this.weather?.weatherType!, this.weather?.turnsLeft!)); // TODO: is this bang correct?
 
     if (this.weather) {
       this.scene.unshiftPhase(new CommonAnimPhase(this.scene, undefined, undefined, CommonAnim.SUNNY + (weather - 1)));
-      this.scene.queueMessage(getWeatherStartMessage(weather));
+      this.scene.queueMessage(getWeatherStartMessage(weather)!); // TODO: is this bang correct?
     } else {
-      this.scene.queueMessage(getWeatherClearMessage(oldWeatherType));
+      this.scene.queueMessage(getWeatherClearMessage(oldWeatherType)!); // TODO: is this bang correct?
     }
 
     this.scene.getField(true).filter(p => p.isOnField()).map(pokemon => {
@@ -339,15 +339,15 @@ export class Arena {
     const oldTerrainType = this.terrain?.terrainType || TerrainType.NONE;
 
     this.terrain = terrain ? new Terrain(terrain, hasPokemonSource ? 5 : 0) : null;
-    this.eventTarget.dispatchEvent(new TerrainChangedEvent(oldTerrainType,this.terrain?.terrainType, this.terrain?.turnsLeft));
+    this.eventTarget.dispatchEvent(new TerrainChangedEvent(oldTerrainType,this.terrain?.terrainType!, this.terrain?.turnsLeft!)); // TODO: are those bangs correct?
 
     if (this.terrain) {
       if (!ignoreAnim) {
         this.scene.unshiftPhase(new CommonAnimPhase(this.scene, undefined, undefined, CommonAnim.MISTY_TERRAIN + (terrain - 1)));
       }
-      this.scene.queueMessage(getTerrainStartMessage(terrain));
+      this.scene.queueMessage(getTerrainStartMessage(terrain)!); // TODO: is this bang correct?
     } else {
-      this.scene.queueMessage(getTerrainClearMessage(oldTerrainType));
+      this.scene.queueMessage(getTerrainClearMessage(oldTerrainType)!); // TODO: is this bang correct?
     }
 
     this.scene.getField(true).filter(p => p.isOnField()).map(pokemon => {
@@ -554,7 +554,7 @@ export class Arena {
     this.applyTagsForSide(tagType, ArenaTagSide.BOTH, ...args);
   }
 
-  addTag(tagType: ArenaTagType, turnCount: integer, sourceMove: Moves, sourceId: integer, side: ArenaTagSide = ArenaTagSide.BOTH, quiet: boolean = false, targetIndex?: BattlerIndex): boolean {
+  addTag(tagType: ArenaTagType, turnCount: integer, sourceMove: Moves | undefined, sourceId: integer, side: ArenaTagSide = ArenaTagSide.BOTH, quiet: boolean = false, targetIndex?: BattlerIndex): boolean {
     const existingTag = this.getTagOnSide(tagType, side);
     if (existingTag) {
       existingTag.onOverlap(this);
@@ -568,21 +568,23 @@ export class Arena {
     }
 
     const newTag = getArenaTag(tagType, turnCount || 0, sourceMove, sourceId, targetIndex, side);
-    this.tags.push(newTag);
-    newTag.onAdd(this, quiet);
+    if (newTag) {
+      this.tags.push(newTag);
+      newTag.onAdd(this, quiet);
 
-    const { layers = 0, maxLayers = 0 } = newTag instanceof ArenaTrapTag ? newTag : {};
+      const { layers = 0, maxLayers = 0 } = newTag instanceof ArenaTrapTag ? newTag : {};
 
-    this.eventTarget.dispatchEvent(new TagAddedEvent(newTag.tagType, newTag.side, newTag.turnCount, layers, maxLayers));
+      this.eventTarget.dispatchEvent(new TagAddedEvent(newTag.tagType, newTag.side, newTag.turnCount, layers, maxLayers));
+    }
 
     return true;
   }
 
-  getTag(tagType: ArenaTagType | Constructor<ArenaTag>): ArenaTag {
+  getTag(tagType: ArenaTagType | Constructor<ArenaTag>): ArenaTag | undefined {
     return this.getTagOnSide(tagType, ArenaTagSide.BOTH);
   }
 
-  getTagOnSide(tagType: ArenaTagType | Constructor<ArenaTag>, side: ArenaTagSide): ArenaTag {
+  getTagOnSide(tagType: ArenaTagType | Constructor<ArenaTag>, side: ArenaTagSide): ArenaTag | undefined {
     return typeof(tagType) === "string"
       ? this.tags.find(t => t.tagType === tagType && (side === ArenaTagSide.BOTH || t.side === ArenaTagSide.BOTH || t.side === side))
       : this.tags.find(t => t instanceof tagType && (side === ArenaTagSide.BOTH || t.side === ArenaTagSide.BOTH || t.side === side));
@@ -724,6 +726,9 @@ export class Arena {
       return 0.000;
     case Biome.SNOWY_FOREST:
       return 3.047;
+    default:
+      console.warn(`missing bgm loop-point for biome "${Biome[this.biomeType]}" (=${this.biomeType})`);
+      return 0;
     }
   }
 }
@@ -777,12 +782,12 @@ export class ArenaBase extends Phaser.GameObjects.Container {
 
     this.player = player;
 
-    this.base = scene.addFieldSprite(0, 0, "plains_a", null, 1);
+    this.base = scene.addFieldSprite(0, 0, "plains_a", undefined, 1);
     this.base.setOrigin(0, 0);
 
     this.props = !player ?
       new Array(3).fill(null).map(() => {
-        const ret = scene.addFieldSprite(0, 0, "plains_b", null, 1);
+        const ret = scene.addFieldSprite(0, 0, "plains_b", undefined, 1);
         ret.setOrigin(0, 0);
         ret.setVisible(false);
         return ret;
diff --git a/src/field/damage-number-handler.ts b/src/field/damage-number-handler.ts
index 4af219a60b9..ae0692da342 100644
--- a/src/field/damage-number-handler.ts
+++ b/src/field/damage-number-handler.ts
@@ -3,6 +3,8 @@ import Pokemon, { DamageResult, HitResult } from "./pokemon";
 import * as Utils from "../utils";
 import { BattlerIndex } from "../battle";
 
+type TextAndShadowArr = [ string | null, string | null ];
+
 export default class DamageNumberHandler {
   private damageNumbers: Map<BattlerIndex, Phaser.GameObjects.Text[]>;
 
@@ -24,7 +26,7 @@ export default class DamageNumberHandler {
     damageNumber.setOrigin(0.5, 1);
     damageNumber.setScale(baseScale);
 
-    let [ textColor, shadowColor ] = [ null, null ];
+    let [ textColor, shadowColor ] : TextAndShadowArr = [ null, null ];
 
     switch (result) {
     case HitResult.SUPER_EFFECTIVE:
@@ -62,12 +64,12 @@ export default class DamageNumberHandler {
       this.damageNumbers.set(battlerIndex, []);
     }
 
-    const yOffset = this.damageNumbers.get(battlerIndex).length * -10;
+    const yOffset = this.damageNumbers.get(battlerIndex)!.length * -10;
     if (yOffset) {
       damageNumber.y += yOffset;
     }
 
-    this.damageNumbers.get(battlerIndex).push(damageNumber);
+    this.damageNumbers.get(battlerIndex)!.push(damageNumber);
 
     if (scene.damageNumbersMode === 1) {
       scene.tweens.add({
@@ -83,7 +85,7 @@ export default class DamageNumberHandler {
         alpha: 0,
         ease: "Sine.easeIn",
         onComplete: () => {
-          this.damageNumbers.get(battlerIndex).splice(this.damageNumbers.get(battlerIndex).indexOf(damageNumber), 1);
+          this.damageNumbers.get(battlerIndex)!.splice(this.damageNumbers.get(battlerIndex)!.indexOf(damageNumber), 1);
           damageNumber.destroy(true);
         }
       });
@@ -167,7 +169,7 @@ export default class DamageNumberHandler {
           delay: Utils.fixedInt(500),
           alpha: 0,
           onComplete: () => {
-            this.damageNumbers.get(battlerIndex).splice(this.damageNumbers.get(battlerIndex).indexOf(damageNumber), 1);
+            this.damageNumbers.get(battlerIndex)!.splice(this.damageNumbers.get(battlerIndex)!.indexOf(damageNumber), 1);
             damageNumber.destroy(true);
           }
         }
diff --git a/src/field/pokemon-sprite-sparkle-handler.ts b/src/field/pokemon-sprite-sparkle-handler.ts
index 5312dd18727..ccf6a098667 100644
--- a/src/field/pokemon-sprite-sparkle-handler.ts
+++ b/src/field/pokemon-sprite-sparkle-handler.ts
@@ -35,7 +35,7 @@ export default class PokemonSpriteSparkleHandler {
       const ratioX = s.width / width;
       const ratioY = s.height / height;
       const pixel = texture.manager.getPixel(pixelX, pixelY, texture.key, "__BASE");
-      if (pixel.alpha) {
+      if (pixel?.alpha) {
         const [ xOffset, yOffset ] = [ -s.originX * s.width, -s.originY * s.height];
         const sparkle = (s.scene as BattleScene).addFieldSprite(((pokemon?.x || 0) + s.x + pixelX * ratioX + xOffset), ((pokemon?.y || 0) + s.y + pixelY * ratioY + yOffset), "tera_sparkle");
         sparkle.pipelineData["ignoreTimeTint"] = s.pipelineData["ignoreTimeTint"];
diff --git a/src/field/pokemon.ts b/src/field/pokemon.ts
index a53076bc856..84058cc656f 100644
--- a/src/field/pokemon.ts
+++ b/src/field/pokemon.ts
@@ -79,8 +79,8 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   public ivs: integer[];
   public nature: Nature;
   public natureOverride: Nature | -1;
-  public moveset: PokemonMove[];
-  public status: Status;
+  public moveset: (PokemonMove | null)[];
+  public status: Status | null;
   public friendship: integer;
   public metLevel: integer;
   public metBiome: Biome | -1;
@@ -89,7 +89,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   public pauseEvolutions: boolean;
   public pokerus: boolean;
 
-  public fusionSpecies: PokemonSpecies;
+  public fusionSpecies: PokemonSpecies | null;
   public fusionFormIndex: integer;
   public fusionAbilityIndex: integer;
   public fusionShiny: boolean;
@@ -97,7 +97,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   public fusionGender: Gender;
   public fusionLuck: integer;
 
-  private summonDataPrimer: PokemonSummonData;
+  private summonDataPrimer: PokemonSummonData | null;
 
   public summonData: PokemonSummonData;
   public battleData: PokemonBattleData;
@@ -107,7 +107,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   public fieldPosition: FieldPosition;
 
   public maskEnabled: boolean;
-  public maskSprite: Phaser.GameObjects.Sprite;
+  public maskSprite: Phaser.GameObjects.Sprite | null;
 
   private shinySparkle: Phaser.GameObjects.Sprite;
 
@@ -169,7 +169,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       this.nickname = dataSource.nickname;
       this.natureOverride = dataSource.natureOverride !== undefined ? dataSource.natureOverride : -1;
       this.moveset = dataSource.moveset;
-      this.status = dataSource.status;
+      this.status = dataSource.status!; // TODO: is this bang correct?
       this.friendship = dataSource.friendship !== undefined ? dataSource.friendship : this.species.baseFriendship;
       this.metLevel = dataSource.metLevel || 5;
       this.luck = dataSource.luck;
@@ -177,7 +177,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       this.metSpecies = dataSource.metSpecies ?? (this.metBiome !== -1 ? this.species.speciesId : this.species.getRootSpeciesId(true));
       this.pauseEvolutions = dataSource.pauseEvolutions;
       this.pokerus = !!dataSource.pokerus;
-      this.fusionSpecies = dataSource.fusionSpecies instanceof PokemonSpecies ? dataSource.fusionSpecies : getPokemonSpecies(dataSource.fusionSpecies);
+      this.fusionSpecies = dataSource.fusionSpecies instanceof PokemonSpecies ? dataSource.fusionSpecies : dataSource.fusionSpecies ? getPokemonSpecies(dataSource.fusionSpecies) : null;
       this.fusionFormIndex = dataSource.fusionFormIndex;
       this.fusionAbilityIndex = dataSource.fusionAbilityIndex;
       this.fusionShiny = dataSource.fusionShiny;
@@ -350,7 +350,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
   loadAssets(ignoreOverride: boolean = true): Promise<void> {
     return new Promise(resolve => {
-      const moveIds = this.getMoveset().map(m => m.getMove().id);
+      const moveIds = this.getMoveset().map(m => m!.getMove().id); // TODO: is this bang correct?
       Promise.allSettled(moveIds.map(m => initMoveAnim(this.scene, m)))
         .then(() => {
           loadMoveAnimAssets(this.scene, moveIds);
@@ -438,7 +438,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     return this.species.forms[this.formIndex].formKey;
   }
 
-  getFusionFormKey(): string {
+  getFusionFormKey(): string | null {
     if (!this.fusionSpecies) {
       return null;
     }
@@ -527,7 +527,8 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       return this.summonData.fusionSpeciesForm;
     }
     if (!this.fusionSpecies?.forms?.length || this.fusionFormIndex >= this.fusionSpecies?.forms.length) {
-      return this.fusionSpecies;
+      //@ts-ignore
+      return this.fusionSpecies; // TODO: I don't even know how to fix this... A complete cluster of classes involved + null
     }
     return this.fusionSpecies?.forms[this.fusionFormIndex];
   }
@@ -536,7 +537,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     return this.getAt(0) as Phaser.GameObjects.Sprite;
   }
 
-  getTintSprite(): Phaser.GameObjects.Sprite {
+  getTintSprite(): Phaser.GameObjects.Sprite | null {
     return !this.maskEnabled
       ? this.getAt(1) as Phaser.GameObjects.Sprite
       : this.maskSprite;
@@ -562,7 +563,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   }
 
   updateSpritePipelineData(): void {
-    [ this.getSprite(), this.getTintSprite() ].map(s => s.pipelineData["teraColor"] = getTypeRgb(this.getTeraType()));
+    [ this.getSprite(), this.getTintSprite() ].filter(s => !!s).map(s => s.pipelineData["teraColor"] = getTypeRgb(this.getTeraType()));
     this.updateInfo(true);
   }
 
@@ -610,7 +611,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   }
 
   playAnim(): void {
-    this.tryPlaySprite(this.getSprite(), this.getTintSprite(), this.getBattleSpriteKey());
+    this.tryPlaySprite(this.getSprite(), this.getTintSprite()!, this.getBattleSpriteKey()); // TODO: is the bag correct?
   }
 
   getFieldPositionOffset(): [ number, number ] {
@@ -870,7 +871,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
   abstract isBoss(): boolean;
 
-  getMoveset(ignoreOverride?: boolean): PokemonMove[] {
+  getMoveset(ignoreOverride?: boolean): (PokemonMove | null)[] {
     const ret = !ignoreOverride && this.summonData?.moveset
       ? this.summonData.moveset
       : this.moveset;
@@ -921,7 +922,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     if (this.metBiome === -1) {
       levelMoves = this.getUnlockedEggMoves().concat(levelMoves);
     }
-    return levelMoves.filter(lm => !this.moveset.some(m => m.moveId === lm));
+    return levelMoves.filter(lm => !this.moveset.some(m => m?.moveId === lm));
   }
 
   /**
@@ -932,7 +933,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
    * @returns array of {@linkcode Type}
    */
   getTypes(includeTeraType = false, forDefend: boolean = false, ignoreOverride?: boolean): Type[] {
-    const types = [];
+    const types : Type[] = [];
 
     if (includeTeraType) {
       const teraType = this.getTeraType();
@@ -942,7 +943,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     }
 
     if (!types.length || !includeTeraType) {
-      if (!ignoreOverride && this.summonData?.types) {
+      if (!ignoreOverride && this.summonData?.types && this.summonData.types.length !== 0) {
         this.summonData.types.forEach(t => types.push(t));
       } else {
         const speciesForm = this.getSpeciesForm(ignoreOverride);
@@ -1115,7 +1116,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
         return false;
       }
     }
-    return (this.hp || ability.isBypassFaint) && !ability.conditions.find(condition => !condition(this));
+    return (!!this.hp || ability.isBypassFaint) && !ability.conditions.find(condition => !condition(this));
   }
 
   /**
@@ -1242,7 +1243,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       ? moveOrType
       : undefined;
     const moveType = (moveOrType instanceof Move)
-      ? move.type
+      ? move!.type // TODO: is this bang correct?
       : moveOrType;
 
     if (moveType === Type.STELLAR) {
@@ -1285,7 +1286,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       }
     }
 
-    return multiplier;
+    return multiplier as TypeDamageMultiplier;
   }
 
   /**
@@ -1327,7 +1328,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     return (atkScore + defScore) * hpDiffRatio;
   }
 
-  getEvolution(): SpeciesFormEvolution {
+  getEvolution(): SpeciesFormEvolution | null {
     if (pokemonEvolutions.hasOwnProperty(this.species.speciesId)) {
       const evolutions = pokemonEvolutions[this.species.speciesId];
       for (const e of evolutions) {
@@ -1339,7 +1340,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       }
     }
 
-    if (this.isFusion() && pokemonEvolutions.hasOwnProperty(this.fusionSpecies.speciesId)) {
+    if (this.isFusion() && this.fusionSpecies && pokemonEvolutions.hasOwnProperty(this.fusionSpecies.speciesId)) {
       const fusionEvolutions = pokemonEvolutions[this.fusionSpecies.speciesId].map(e => new FusionSpeciesFormEvolution(this.species.speciesId, e));
       for (const fe of fusionEvolutions) {
         if (!fe.item && this.level >= fe.level && (!fe.preFormKey || this.getFusionFormKey() === fe.preFormKey)) {
@@ -1549,7 +1550,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   }
 
   clearFusionSpecies(): void {
-    this.fusionSpecies = undefined;
+    this.fusionSpecies = null;
     this.fusionFormIndex = 0;
     this.fusionAbilityIndex = 0;
     this.fusionShiny = false;
@@ -1709,9 +1710,9 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
         // Sqrt the weight of any damaging moves with overlapping types. This is about a 0.05 - 0.1 multiplier.
         // Other damaging moves 2x weight if 0-1 damaging moves, 0.5x if 2, 0.125x if 3. These weights double if STAB.
         // Status moves remain unchanged on weight, this encourages 1-2
-        movePool = baseWeights.filter(m => !this.moveset.some(mo => m[0] === mo.moveId)).map(m => [m[0], this.moveset.some(mo => mo.getMove().category !== MoveCategory.STATUS && mo.getMove().type === allMoves[m[0]].type) ? Math.ceil(Math.sqrt(m[1])) : allMoves[m[0]].category !== MoveCategory.STATUS ? Math.ceil(m[1]/Math.max(Math.pow(4, this.moveset.filter(mo => mo.getMove().power > 1).length)/8,0.5) * (this.isOfType(allMoves[m[0]].type) ? 2 : 1)) : m[1]]);
+        movePool = baseWeights.filter(m => !this.moveset.some(mo => m[0] === mo?.moveId)).map(m => [m[0], this.moveset.some(mo => mo?.getMove().category !== MoveCategory.STATUS && mo?.getMove().type === allMoves[m[0]].type) ? Math.ceil(Math.sqrt(m[1])) : allMoves[m[0]].category !== MoveCategory.STATUS ? Math.ceil(m[1]/Math.max(Math.pow(4, this.moveset.filter(mo => (mo?.getMove().power!) > 1).length)/8,0.5) * (this.isOfType(allMoves[m[0]].type) ? 2 : 1)) : m[1]]); // TODO: is this bang correct?
       } else { // Non-trainer pokemon just use normal weights
-        movePool = baseWeights.filter(m => !this.moveset.some(mo => m[0] === mo.moveId));
+        movePool = baseWeights.filter(m => !this.moveset.some(mo => m[0] === mo?.moveId));
       }
       const totalWeight = movePool.reduce((v, m) => v + m[1], 0);
       let rand = Utils.randSeedInt(totalWeight);
@@ -1729,7 +1730,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     const move = this.getMoveset().length > moveIndex
       ? this.getMoveset()[moveIndex]
       : null;
-    return move?.isUsable(this, ignorePp);
+    return move?.isUsable(this, ignorePp)!; // TODO: is this bang correct?
   }
 
   showInfo(): void {
@@ -1812,7 +1813,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     this.levelExp = this.exp - getLevelTotalExp(this.level, this.species.growthRate);
   }
 
-  getOpponent(targetIndex: integer): Pokemon {
+  getOpponent(targetIndex: integer): Pokemon | null {
     const ret = this.getOpponents()[targetIndex];
     if (ret.summonData) {
       return ret;
@@ -1977,7 +1978,8 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
           this.scene.applyModifiers(CritBoosterModifier, source.isPlayer(), source, critLevel);
           this.scene.applyModifiers(TempBattleStatBoosterModifier, source.isPlayer(), TempBattleStat.CRIT, critLevel);
           const bonusCrit = new Utils.BooleanHolder(false);
-          if (applyAbAttrs(BonusCritAbAttr, source, null, bonusCrit)) {
+          //@ts-ignore
+          if (applyAbAttrs(BonusCritAbAttr, source, null, bonusCrit)) { // TODO: resolve ts-ignore. This is a promise. Checking a promise is bogus.
             if (bonusCrit.value) {
               critLevel.value += 1;
             }
@@ -2000,7 +2002,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
             isCritical = false;
           }
         }
-        const sourceAtk = new Utils.IntegerHolder(source.getBattleStat(isPhysical ? Stat.ATK : Stat.SPATK, this, null, isCritical));
+        const sourceAtk = new Utils.IntegerHolder(source.getBattleStat(isPhysical ? Stat.ATK : Stat.SPATK, this, undefined, isCritical));
         const targetDef = new Utils.IntegerHolder(this.getBattleStat(isPhysical ? Stat.DEF : Stat.SPDEF, source, move, isCritical));
         const criticalMultiplier = new Utils.NumberHolder(isCritical ? 1.5 : 1);
         applyAbAttrs(MultCritAbAttr, source, null, criticalMultiplier);
@@ -2088,6 +2090,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
           isCritical = false;
           result = HitResult.EFFECTIVE;
         }
+        result = result!; // telling TS compiler that result is defined!
 
         if (!result) {
           if (!typeMultiplier.value) {
@@ -2192,7 +2195,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
         }
 
         if (damage) {
-          const attacker = this.scene.getPokemonById(source.id);
+          const attacker = this.scene.getPokemonById(source.id)!; // TODO: is this bang correct?
           destinyTag?.lapse(attacker, BattlerTagLapseType.CUSTOM);
         }
       }
@@ -2292,7 +2295,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
   isMax(): boolean {
     const maxForms = [SpeciesFormKey.GIGANTAMAX, SpeciesFormKey.GIGANTAMAX_RAPID, SpeciesFormKey.GIGANTAMAX_SINGLE, SpeciesFormKey.ETERNAMAX] as string[];
-    return maxForms.includes(this.getFormKey()) || maxForms.includes(this.getFusionFormKey());
+    return maxForms.includes(this.getFormKey()) || (!!this.getFusionFormKey() && maxForms.includes(this.getFusionFormKey()!));
   }
 
   addTag(tagType: BattlerTagType, turnCount: integer = 0, sourceMove?: Moves, sourceId?: integer): boolean {
@@ -2302,7 +2305,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       return false;
     }
 
-    const newTag = getBattlerTag(tagType, turnCount, sourceMove, sourceId);
+    const newTag = getBattlerTag(tagType, turnCount, sourceMove!, sourceId!); // TODO: are the bangs correct?
 
     const cancelled = new Utils.BooleanHolder(false);
     applyPreApplyBattlerTagAbAttrs(BattlerTagImmunityAbAttr, this, newTag, cancelled);
@@ -2321,18 +2324,19 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   }
 
   /** @overload */
-  getTag(tagType: BattlerTagType): BattlerTag;
+  getTag(tagType: BattlerTagType): BattlerTag | null;
 
   /** @overload */
-  getTag<T extends BattlerTag>(tagType: Constructor<T>): T;
+  getTag<T extends BattlerTag>(tagType: Constructor<T>): T | null;
 
-  getTag(tagType: BattlerTagType | Constructor<BattlerTag>): BattlerTag {
+  getTag(tagType: BattlerTagType | Constructor<BattlerTag>): BattlerTag | null {
     if (!this.summonData) {
       return null;
     }
-    return tagType instanceof Function
+    return (tagType instanceof Function
       ? this.summonData.tags.find(t => t instanceof tagType)
-      : this.summonData.tags.find(t => t.tagType === tagType);
+      : this.summonData.tags.find(t => t.tagType === tagType)
+    )!; // TODO: is this bang correct?
   }
 
   findTag(tagFilter: ((tag: BattlerTag) => boolean)) {
@@ -2436,7 +2440,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     this.getMoveHistory().push(turnMove);
   }
 
-  getLastXMoves(turnCount?: integer): TurnMove[] {
+  getLastXMoves(turnCount: integer = 0): TurnMove[] {
     const moveHistory = this.getMoveHistory();
     return moveHistory.slice(turnCount >= 0 ? Math.max(moveHistory.length - (turnCount || 1), 0) : 0, moveHistory.length).reverse();
   }
@@ -2514,9 +2518,9 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     let frameThreshold: number;
 
     sprite.anims.pause();
-    tintSprite.anims.pause();
+    tintSprite?.anims.pause();
 
-    let faintCryTimer = this.scene.time.addEvent({
+    let faintCryTimer : Phaser.Time.TimerEvent | null = this.scene.time.addEvent({
       delay: Utils.fixedInt(delay),
       repeat: -1,
       callback: () => {
@@ -2526,7 +2530,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
         while (frameProgress > frameThreshold) {
           if (sprite.anims.duration) {
             sprite.anims.nextFrame();
-            tintSprite.anims.nextFrame();
+            tintSprite?.anims.nextFrame();
           }
           frameProgress -= frameThreshold;
         }
@@ -2534,7 +2538,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
           rate *= 0.99;
           cry.setRate(rate);
         } else {
-          faintCryTimer.destroy();
+          faintCryTimer?.destroy();
           faintCryTimer = null;
           if (callback) {
             callback();
@@ -2593,9 +2597,9 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     let frameThreshold: number;
 
     sprite.anims.pause();
-    tintSprite.anims.pause();
+    tintSprite?.anims.pause();
 
-    let faintCryTimer = this.scene.time.addEvent({
+    let faintCryTimer: Phaser.Time.TimerEvent | null = this.scene.time.addEvent({
       delay: Utils.fixedInt(delay),
       repeat: -1,
       callback: () => {
@@ -2605,7 +2609,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
         while (frameProgress > frameThreshold) {
           if (sprite.anims.duration) {
             sprite.anims.nextFrame();
-            tintSprite.anims.nextFrame();
+            tintSprite?.anims.nextFrame();
           }
           frameProgress -= frameThreshold;
         }
@@ -2622,7 +2626,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
           fusionCry.setRate(rate);
         }
         if ((!cry || cry.pendingRemove) && (!fusionCry || fusionCry.pendingRemove)) {
-          faintCryTimer.destroy();
+          faintCryTimer?.destroy();
           faintCryTimer = null;
           if (callback) {
             callback();
@@ -2653,7 +2657,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     return this.gender !== Gender.GENDERLESS && pokemon.gender === (this.gender === Gender.MALE ? Gender.FEMALE : Gender.MALE);
   }
 
-  canSetStatus(effect: StatusEffect, quiet: boolean = false, overrideStatus: boolean = false, sourcePokemon: Pokemon = null): boolean {
+  canSetStatus(effect: StatusEffect | undefined, quiet: boolean = false, overrideStatus: boolean = false, sourcePokemon: Pokemon | null = null): boolean {
     if (effect !== StatusEffect.FAINT) {
       if (overrideStatus ? this.status?.effect === effect : this.status) {
         return false;
@@ -2704,7 +2708,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       }
       break;
     case StatusEffect.FREEZE:
-      if (this.isOfType(Type.ICE) || [WeatherType.SUNNY, WeatherType.HARSH_SUN].includes(this.scene?.arena.weather?.weatherType)) {
+      if (this.isOfType(Type.ICE) || (this.scene?.arena?.weather?.weatherType &&[WeatherType.SUNNY, WeatherType.HARSH_SUN].includes(this.scene.arena.weather.weatherType))) {
         return false;
       }
       break;
@@ -2728,7 +2732,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     return true;
   }
 
-  trySetStatus(effect: StatusEffect, asPhase: boolean = false, sourcePokemon: Pokemon = null, cureTurn: integer = 0, sourceText: string = null): boolean {
+  trySetStatus(effect: StatusEffect | undefined, asPhase: boolean = false, sourcePokemon: Pokemon | null = null, cureTurn: integer | null = 0, sourceText: string | null = null): boolean {
     if (!this.canSetStatus(effect, asPhase, false, sourcePokemon)) {
       return false;
     }
@@ -2742,7 +2746,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     }
 
     if (asPhase) {
-      this.scene.unshiftPhase(new ObtainStatusEffectPhase(this.scene, this.getBattlerIndex(), effect, cureTurn, sourceText, sourcePokemon));
+      this.scene.unshiftPhase(new ObtainStatusEffectPhase(this.scene, this.getBattlerIndex(), effect, cureTurn, sourceText!, sourcePokemon!)); // TODO: are these bangs correct?
       return true;
     }
 
@@ -2770,6 +2774,8 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       }
     }
 
+    statusCureTurn = statusCureTurn!; // tell TS compiler it's defined
+    effect = effect!; // If `effect` is undefined then `trySetStatus()` will have already returned early via the `canSetStatus()` call
     this.status = new Status(effect, 0, statusCureTurn?.value);
 
     if (effect !== StatusEffect.FAINT) {
@@ -2790,7 +2796,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     if (!revive && lastStatus === StatusEffect.FAINT) {
       return;
     }
-    this.status = undefined;
+    this.status = null;
     if (lastStatus === StatusEffect.SLEEP) {
       this.setFrameRate(12);
       if (this.getTag(BattlerTagType.NIGHTMARE)) {
@@ -2858,16 +2864,16 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   setFrameRate(frameRate: integer) {
     this.scene.anims.get(this.getBattleSpriteKey()).frameRate = frameRate;
     this.getSprite().play(this.getBattleSpriteKey());
-    this.getTintSprite().play(this.getBattleSpriteKey());
+    this.getTintSprite()?.play(this.getBattleSpriteKey());
   }
 
   tint(color: number, alpha?: number, duration?: integer, ease?: string) {
     const tintSprite = this.getTintSprite();
-    tintSprite.setTintFill(color);
-    tintSprite.setVisible(true);
+    tintSprite?.setTintFill(color);
+    tintSprite?.setVisible(true);
 
     if (duration) {
-      tintSprite.setAlpha(0);
+      tintSprite?.setAlpha(0);
 
       this.scene.tweens.add({
         targets: tintSprite,
@@ -2876,7 +2882,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
         ease: ease || "Linear"
       });
     } else {
-      tintSprite.setAlpha(alpha);
+      tintSprite?.setAlpha(alpha);
     }
   }
 
@@ -2890,32 +2896,32 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
         duration: duration,
         ease: ease || "Linear",
         onComplete: () => {
-          tintSprite.setVisible(false);
-          tintSprite.setAlpha(1);
+          tintSprite?.setVisible(false);
+          tintSprite?.setAlpha(1);
         }
       });
     } else {
-      tintSprite.setVisible(false);
-      tintSprite.setAlpha(1);
+      tintSprite?.setVisible(false);
+      tintSprite?.setAlpha(1);
     }
   }
 
   enableMask() {
     if (!this.maskEnabled) {
       this.maskSprite = this.getTintSprite();
-      this.maskSprite.setVisible(true);
-      this.maskSprite.setPosition(this.x * this.parentContainer.scale + this.parentContainer.x,
+      this.maskSprite?.setVisible(true);
+      this.maskSprite?.setPosition(this.x * this.parentContainer.scale + this.parentContainer.x,
         this.y * this.parentContainer.scale + this.parentContainer.y);
-      this.maskSprite.setScale(this.getSpriteScale() * this.parentContainer.scale);
+      this.maskSprite?.setScale(this.getSpriteScale() * this.parentContainer.scale);
       this.maskEnabled = true;
     }
   }
 
   disableMask() {
     if (this.maskEnabled) {
-      this.maskSprite.setVisible(false);
-      this.maskSprite.setPosition(0, 0);
-      this.maskSprite.setScale(this.getSpriteScale());
+      this.maskSprite?.setVisible(false);
+      this.maskSprite?.setPosition(0, 0);
+      this.maskSprite?.setScale(this.getSpriteScale());
       this.maskSprite = null;
       this.maskEnabled = false;
     }
@@ -2930,7 +2936,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
   updateFusionPalette(ignoreOveride?: boolean): void {
     if (!this.getFusionSpeciesForm(ignoreOveride)) {
-      [ this.getSprite(), this.getTintSprite() ].map(s => {
+      [ this.getSprite(), this.getTintSprite() ].filter(s => !!s).map(s => {
         s.pipelineData[`spriteColors${ignoreOveride && this.summonData?.speciesForm ? "Base" : ""}`] = [];
         s.pipelineData[`fusionSpriteColors${ignoreOveride && this.summonData?.speciesForm ? "Base" : ""}`] = [];
       });
@@ -2966,9 +2972,12 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       const frame = [ sourceFrame, sourceBackFrame, fusionFrame, fusionBackFrame ][c];
       canv.width = frame.width;
       canv.height = frame.height;
-      context.drawImage([ sourceImage, sourceBackImage, fusionImage, fusionBackImage ][c], frame.cutX, frame.cutY, frame.width, frame.height, 0, 0, frame.width, frame.height);
-      const imageData = context.getImageData(frame.cutX, frame.cutY, frame.width, frame.height);
-      pixelData.push(imageData.data);
+
+      if (context) {
+        context.drawImage([ sourceImage, sourceBackImage, fusionImage, fusionBackImage ][c], frame.cutX, frame.cutY, frame.width, frame.height, 0, 0, frame.width, frame.height);
+        const imageData = context.getImageData(frame.cutX, frame.cutY, frame.width, frame.height);
+        pixelData.push(imageData.data);
+      }
     });
 
     for (let f = 0; f < 2; f++) {
@@ -2988,7 +2997,9 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
             const color = Utils.rgbaToInt([r, g, b, a]);
             if (variantColorSet.has(color)) {
               const mappedPixel = variantColorSet.get(color);
-              [ r, g, b, a ] = mappedPixel;
+              if (mappedPixel) {
+                [ r, g, b, a ] = mappedPixel;
+              }
             }
           }
           if (!spriteColors.find(c => c[0] === r && c[1] === g && c[2] === b)) {
@@ -3000,7 +3011,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
     const fusionSpriteColors = JSON.parse(JSON.stringify(spriteColors));
 
-    const pixelColors = [];
+    const pixelColors: number[] = [];
     for (let f = 0; f < 2; f++) {
       for (let i = 0; i < pixelData[f].length; i += 4) {
         const total = pixelData[f].slice(i, i + 3).reduce((total: integer, value: integer) => total + value, 0);
@@ -3011,7 +3022,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       }
     }
 
-    const fusionPixelColors = [];
+    const fusionPixelColors : number[] = [];
     for (let f = 0; f < 2; f++) {
       const variantColors = variantColorCache[!f ? fusionSpriteKey : fusionBackSpriteKey];
       const variantColorSet = new Map<integer, integer[]>();
@@ -3030,7 +3041,9 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
           const color = Utils.rgbaToInt([r, g, b, a]);
           if (variantColorSet.has(color)) {
             const mappedPixel = variantColorSet.get(color);
-            [ r, g, b, a ] = mappedPixel;
+            if (mappedPixel) {
+              [ r, g, b, a ] = mappedPixel;
+            }
           }
         }
         fusionPixelColors.push(argbFromRgba({ r, g, b, a }));
@@ -3050,9 +3063,11 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
     Math.random = originalRandom;
 
+    paletteColors = paletteColors!; // tell TS compiler that paletteColors is defined!
+    fusionPaletteColors = fusionPaletteColors!; // TS compiler that fusionPaletteColors is defined!
     const [ palette, fusionPalette ] = [ paletteColors, fusionPaletteColors ]
       .map(paletteColors => {
-        let keys = Array.from(paletteColors.keys()).sort((a: integer, b: integer) => paletteColors.get(a) < paletteColors.get(b) ? 1 : -1);
+        let keys = Array.from(paletteColors.keys()).sort((a: integer, b: integer) => paletteColors.get(a)! < paletteColors.get(b)! ? 1 : -1);
         let rgbaColors: Map<number, integer[]>;
         let hsvColors: Map<number, number[]>;
 
@@ -3065,19 +3080,19 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
             map.set(k, Object.values(rgbaFromArgb(k))); return map;
           }, new Map<number, integer[]>());
           hsvColors = Array.from(rgbaColors.keys()).reduce((map: Map<number, number[]>, k: number) => {
-            const rgb = rgbaColors.get(k).slice(0, 3);
+            const rgb = rgbaColors.get(k)!.slice(0, 3);
             map.set(k, Utils.rgbToHsv(rgb[0], rgb[1], rgb[2]));
             return map;
           }, new Map<number, number[]>());
 
           for (let c = keys.length - 1; c >= 0; c--) {
-            const hsv = hsvColors.get(keys[c]);
+            const hsv = hsvColors.get(keys[c])!;
             for (let c2 = 0; c2 < c; c2++) {
-              const hsv2 = hsvColors.get(keys[c2]);
+              const hsv2 = hsvColors.get(keys[c2])!;
               const diff = Math.abs(hsv[0] - hsv2[0]);
               if (diff < 30 || diff >= 330) {
                 if (mappedColors.has(keys[c])) {
-                  mappedColors.get(keys[c]).push(keys[c2]);
+                  mappedColors.get(keys[c])!.push(keys[c2]);
                 } else {
                   mappedColors.set(keys[c], [ keys[c2] ]);
                 }
@@ -3087,10 +3102,10 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
           }
 
           mappedColors.forEach((values: integer[], key: integer) => {
-            const keyColor = rgbaColors.get(key);
-            const valueColors = values.map(v => rgbaColors.get(v));
+            const keyColor = rgbaColors.get(key)!;
+            const valueColors = values.map(v => rgbaColors.get(v)!);
             const color = keyColor.slice(0);
-            let count = paletteColors.get(key);
+            let count = paletteColors.get(key)!;
             for (const value of values) {
               const valueCount = paletteColors.get(value);
               if (!valueCount) {
@@ -3100,10 +3115,10 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
             }
 
             for (let c = 0; c < 3; c++) {
-              color[c] *= (paletteColors.get(key) / count);
+              color[c] *= (paletteColors.get(key)! / count);
               values.forEach((value: integer, i: integer) => {
                 if (paletteColors.has(value)) {
-                  const valueCount = paletteColors.get(value);
+                  const valueCount = paletteColors.get(value)!;
                   color[c] += valueColors[i][c] * (valueCount / count);
                 }
               });
@@ -3121,7 +3136,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
             paletteColors.set(argbFromRgba({ r: color[0], g: color[1], b: color[2], a: color[3] }), count);
           });
 
-          keys = Array.from(paletteColors.keys()).sort((a: integer, b: integer) => paletteColors.get(a) < paletteColors.get(b) ? 1 : -1);
+          keys = Array.from(paletteColors.keys()).sort((a: integer, b: integer) => paletteColors.get(a)! < paletteColors.get(b)! ? 1 : -1);
         } while (mappedColors.size);
 
         return keys.map(c => Object.values(rgbaFromArgb(c)));
@@ -3152,7 +3167,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       }
     }
 
-    [ this.getSprite(), this.getTintSprite() ].map(s => {
+    [ this.getSprite(), this.getTintSprite() ].filter(s => !!s).map(s => {
       s.pipelineData[`spriteColors${ignoreOveride && this.summonData?.speciesForm ? "Base" : ""}`] = spriteColors;
       s.pipelineData[`fusionSpriteColors${ignoreOveride && this.summonData?.speciesForm ? "Base" : ""}`] = fusionSpriteColors;
     });
@@ -3216,7 +3231,7 @@ export default interface Pokemon {
 export class PlayerPokemon extends Pokemon {
   public compatibleTms: Moves[];
 
-  constructor(scene: BattleScene, species: PokemonSpecies, level: integer, abilityIndex: integer, formIndex: integer, gender: Gender, shiny: boolean, variant: Variant, ivs: integer[], nature: Nature, dataSource: Pokemon | PokemonData) {
+  constructor(scene: BattleScene, species: PokemonSpecies, level: integer, abilityIndex?: integer, formIndex?: integer, gender?: Gender, shiny?: boolean, variant?: Variant, ivs?: integer[], nature?: Nature, dataSource?: Pokemon | PokemonData) {
     super(scene, 106, 148, species, level, abilityIndex, formIndex, gender, shiny, variant, ivs, nature, dataSource);
 
     if (Overrides.STATUS_OVERRIDE) {
@@ -3320,11 +3335,11 @@ export class PlayerPokemon extends Pokemon {
 
   addFriendship(friendship: integer): void {
     const starterSpeciesId = this.species.getRootSpeciesId();
-    const fusionStarterSpeciesId = this.isFusion() ? this.fusionSpecies.getRootSpeciesId() : 0;
+    const fusionStarterSpeciesId = this.isFusion() && this.fusionSpecies ? this.fusionSpecies.getRootSpeciesId() : 0;
     const starterData = [
       this.scene.gameData.starterData[starterSpeciesId],
       fusionStarterSpeciesId ? this.scene.gameData.starterData[fusionStarterSpeciesId] : null
-    ].filter(d => d);
+    ].filter(d => !!d);
     const amount = new Utils.IntegerHolder(friendship);
     const starterAmount = new Utils.IntegerHolder(Math.floor(friendship * (this.scene.gameMode.isClassic && friendship > 0 ? 2 : 1) / (fusionStarterSpeciesId ? 2 : 1)));
     if (amount.value > 0) {
@@ -3388,7 +3403,10 @@ export class PlayerPokemon extends Pokemon {
     });
   }
 
-  getPossibleEvolution(evolution: SpeciesFormEvolution): Promise<Pokemon> {
+  getPossibleEvolution(evolution: SpeciesFormEvolution | null): Promise<Pokemon> {
+    if (!evolution) {
+      return new Promise(resolve => resolve(this));
+    }
     return new Promise(resolve => {
       const evolutionSpecies = getPokemonSpecies(evolution.speciesId);
       const isFusion = evolution instanceof FusionSpeciesFormEvolution;
@@ -3409,7 +3427,10 @@ export class PlayerPokemon extends Pokemon {
     });
   }
 
-  evolve(evolution: SpeciesFormEvolution, preEvolution: PokemonSpeciesForm): Promise<void> {
+  evolve(evolution: SpeciesFormEvolution | null, preEvolution: PokemonSpeciesForm): Promise<void> {
+    if (!evolution) {
+      return new Promise(resolve => resolve());
+    }
     return new Promise(resolve => {
       this.pauseEvolutions = false;
       // Handles Nincada evolving into Ninjask + Shedinja
@@ -3421,7 +3442,7 @@ export class PlayerPokemon extends Pokemon {
         this.fusionSpecies = getPokemonSpecies(evolution.speciesId);
       }
       if (evolution.preFormKey !== null) {
-        const formIndex = Math.max((!isFusion ? this.species : this.fusionSpecies).forms.findIndex(f => f.formKey === evolution.evoFormKey), 0);
+        const formIndex = Math.max((!isFusion || !this.fusionSpecies ? this.species : this.fusionSpecies).forms.findIndex(f => f.formKey === evolution.evoFormKey), 0);
         if (!isFusion) {
           this.formIndex = formIndex;
         } else {
@@ -3477,10 +3498,10 @@ export class PlayerPokemon extends Pokemon {
     const isFusion = evolution instanceof FusionSpeciesFormEvolution;
 
     const evoSpecies = (!isFusion ? this.species : this.fusionSpecies);
-    if (evoSpecies.speciesId === Species.NINCADA && evolution.speciesId === Species.NINJASK) {
+    if (evoSpecies?.speciesId === Species.NINCADA && evolution.speciesId === Species.NINJASK) {
       const newEvolution = pokemonEvolutions[evoSpecies.speciesId][1];
 
-      if (newEvolution.condition.predicate(this)) {
+      if (newEvolution.condition?.predicate(this)) {
         const newPokemon = this.scene.addPlayerPokemon(this.species, this.level, this.abilityIndex, this.formIndex, undefined, this.shiny, this.variant, this.ivs, this.nature);
         newPokemon.natureOverride = this.natureOverride;
         newPokemon.passive = this.passive;
@@ -3576,7 +3597,7 @@ export class PlayerPokemon extends Pokemon {
       if (!this.isFainted()) {
         // If this Pokemon hasn't fainted, make sure the HP wasn't set over the new maximum
         this.hp = Math.min(this.hp, this.stats[Stat.HP]);
-        this.status = getRandomStatus(this.status, pokemon.status); // Get a random valid status between the two
+        this.status = getRandomStatus(this.status!, pokemon.status!); // Get a random valid status between the two  // TODO: are the bangs correct?
       } else if (!pokemon.isFainted()) {
         // If this Pokemon fainted but the other hasn't, make sure the HP wasn't set to zero
         this.hp = Math.max(this.hp, 1);
@@ -3601,7 +3622,7 @@ export class PlayerPokemon extends Pokemon {
           this.scene.removePartyMemberModifiers(fusedPartyMemberIndex);
           this.scene.getParty().splice(fusedPartyMemberIndex, 1)[0];
           const newPartyMemberIndex = this.scene.getParty().indexOf(this);
-          pokemon.getMoveset(true).map(m => this.scene.unshiftPhase(new LearnMovePhase(this.scene, newPartyMemberIndex, m.getMove().id)));
+          pokemon.getMoveset(true).map(m => this.scene.unshiftPhase(new LearnMovePhase(this.scene, newPartyMemberIndex, m!.getMove().id))); // TODO: is the bang correct?
           pokemon.destroy();
           this.updateFusionPalette();
           resolve();
@@ -3621,9 +3642,9 @@ export class PlayerPokemon extends Pokemon {
 
   /** Returns a deep copy of this Pokemon's moveset array */
   copyMoveset(): PokemonMove[] {
-    const newMoveset = [];
+    const newMoveset : PokemonMove[] = [];
     this.moveset.forEach(move =>
-      newMoveset.push(new PokemonMove(move.moveId, 0, move.ppUp, move.virtual)));
+      newMoveset.push(new PokemonMove(move!.moveId, 0, move!.ppUp, move!.virtual))); // TODO: are those bangs correct?
 
     return newMoveset;
   }
@@ -3637,9 +3658,9 @@ export class EnemyPokemon extends Pokemon {
   /** To indicate of the instance was populated with a dataSource -> e.g. loaded & populated from session data */
   public readonly isPopulatedFromDataSource: boolean;
 
-  constructor(scene: BattleScene, species: PokemonSpecies, level: integer, trainerSlot: TrainerSlot, boss: boolean, dataSource: PokemonData) {
+  constructor(scene: BattleScene, species: PokemonSpecies, level: integer, trainerSlot: TrainerSlot, boss: boolean, dataSource?: PokemonData) {
     super(scene, 236, 84, species, level, dataSource?.abilityIndex, dataSource?.formIndex,
-      dataSource?.gender, dataSource ? dataSource.shiny : false, dataSource ? dataSource.variant : undefined, null, dataSource ? dataSource.nature : undefined, dataSource);
+      dataSource?.gender, dataSource ? dataSource.shiny : false, dataSource ? dataSource.variant : undefined, undefined, dataSource ? dataSource.nature : undefined, dataSource);
 
     this.trainerSlot = trainerSlot;
     this.isPopulatedFromDataSource = !!dataSource; // if a dataSource is provided, then it was populated from dataSource
@@ -3672,7 +3693,7 @@ export class EnemyPokemon extends Pokemon {
       let speciesId = species.speciesId;
       while ((prevolution = pokemonPrevolutions[speciesId])) {
         const evolution = pokemonEvolutions[prevolution].find(pe => pe.speciesId === speciesId && (!pe.evoFormKey || pe.evoFormKey === this.getFormKey()));
-        if (evolution.condition?.enforceFunc) {
+        if (evolution?.condition?.enforceFunc) {
           evolution.condition.enforceFunc(this);
         }
         speciesId = prevolution;
@@ -3748,7 +3769,7 @@ export class EnemyPokemon extends Pokemon {
   getNextMove(): QueuedMove {
     // If this Pokemon has a move already queued, return it.
     const queuedMove = this.getMoveQueue().length
-      ? this.getMoveset().find(m => m.moveId === this.getMoveQueue()[0].move)
+      ? this.getMoveset().find(m => m?.moveId === this.getMoveQueue()[0].move)
       : null;
     if (queuedMove) {
       if (queuedMove.isUsable(this, this.getMoveQueue()[0].ignorePP)) {
@@ -3760,24 +3781,24 @@ export class EnemyPokemon extends Pokemon {
     }
 
     // Filter out any moves this Pokemon cannot use
-    const movePool = this.getMoveset().filter(m => m.isUsable(this));
+    const movePool = this.getMoveset().filter(m => m?.isUsable(this));
     // If no moves are left, use Struggle. Otherwise, continue with move selection
     if (movePool.length) {
       // If there's only 1 move in the move pool, use it.
       if (movePool.length === 1) {
-        return { move: movePool[0].moveId, targets: this.getNextTargets(movePool[0].moveId) };
+        return { move: movePool[0]!.moveId, targets: this.getNextTargets(movePool[0]!.moveId) }; // TODO: are the bangs correct?
       }
       // If a move is forced because of Encore, use it.
       const encoreTag = this.getTag(EncoreTag) as EncoreTag;
       if (encoreTag) {
-        const encoreMove = movePool.find(m => m.moveId === encoreTag.moveId);
+        const encoreMove = movePool.find(m => m?.moveId === encoreTag.moveId);
         if (encoreMove) {
           return { move: encoreMove.moveId, targets: this.getNextTargets(encoreMove.moveId) };
         }
       }
       switch (this.aiType) {
       case AiType.RANDOM: // No enemy should spawn with this AI type in-game
-        const moveId = movePool[this.scene.randBattleSeedInt(movePool.length)].moveId;
+        const moveId = movePool[this.scene.randBattleSeedInt(movePool.length)]!.moveId; // TODO: is the bang correct?
         return { move: moveId, targets: this.getNextTargets(moveId) };
       case AiType.SMART_RANDOM:
       case AiType.SMART:
@@ -3787,9 +3808,9 @@ export class EnemyPokemon extends Pokemon {
          * For more information on how benefit scores are calculated, see `docs/enemy-ai.md`.
          */
         const moveScores = movePool.map(() => 0);
-        const moveTargets = Object.fromEntries(movePool.map(m => [ m.moveId, this.getNextTargets(m.moveId) ]));
+        const moveTargets = Object.fromEntries(movePool.map(m => [ m!.moveId, this.getNextTargets(m!.moveId) ])); // TODO: are those bangs correct?
         for (const m in movePool) {
-          const pokemonMove = movePool[m];
+          const pokemonMove = movePool[m]!; // TODO: is the bang correct?
           const move = pokemonMove.getMove();
 
           let moveScore = moveScores[m];
@@ -3870,8 +3891,8 @@ export class EnemyPokemon extends Pokemon {
             r++;
           }
         }
-        console.log(movePool.map(m => m.getName()), moveScores, r, sortedMovePool.map(m => m.getName()));
-        return { move: sortedMovePool[r].moveId, targets: moveTargets[sortedMovePool[r].moveId] };
+        console.log(movePool.map(m => m!.getName()), moveScores, r, sortedMovePool.map(m => m!.getName())); // TODO: are those bangs correct?
+        return { move: sortedMovePool[r]!.moveId, targets: moveTargets[sortedMovePool[r]!.moveId] };
       }
     }
 
@@ -3934,7 +3955,7 @@ export class EnemyPokemon extends Pokemon {
     }
 
     const thresholds: integer[] = [];
-    let totalWeight: integer;
+    let totalWeight: integer = 0;
     targetWeights.reduce((total: integer, w: integer) => {
       total += w;
       thresholds.push(total);
@@ -3948,7 +3969,7 @@ export class EnemyPokemon extends Pokemon {
      * is greater than that random number.
      */
     const randValue = this.scene.randBattleSeedInt(totalWeight);
-    let targetIndex: integer;
+    let targetIndex: integer = 0;
 
     thresholds.every((t, i) => {
       if (randValue >= t) {
@@ -4124,7 +4145,7 @@ export class EnemyPokemon extends Pokemon {
 
   addToParty(pokeballType: PokeballType) {
     const party = this.scene.getParty();
-    let ret: PlayerPokemon = null;
+    let ret: PlayerPokemon | null = null;
 
     if (party.length < 6) {
       this.pokeball = pokeballType;
@@ -4173,15 +4194,15 @@ export class PokemonSummonData {
   public abilitySuppressed: boolean = false;
   public abilitiesApplied: Abilities[] = [];
 
-  public speciesForm: PokemonSpeciesForm;
+  public speciesForm: PokemonSpeciesForm | null;
   public fusionSpeciesForm: PokemonSpeciesForm;
   public ability: Abilities = Abilities.NONE;
   public gender: Gender;
   public fusionGender: Gender;
   public stats: integer[];
-  public moveset: PokemonMove[];
+  public moveset: (PokemonMove | null)[];
   // If not initialized this value will not be populated from save data.
-  public types: Type[] = null;
+  public types: Type[] = [];
 }
 
 export class PokemonBattleData {
diff --git a/src/field/trainer.ts b/src/field/trainer.ts
index 470e8d2267f..1348749d964 100644
--- a/src/field/trainer.ts
+++ b/src/field/trainer.ts
@@ -208,7 +208,7 @@ export default class Trainer extends Phaser.GameObjects.Container {
   }
 
   getPartyLevels(waveIndex: integer): integer[] {
-    const ret = [];
+    const ret: number[] = [];
     const partyTemplate = this.getPartyTemplate();
 
     const difficultyWaveIndex = this.scene.gameMode.getWaveForDifficulty(waveIndex);
@@ -257,7 +257,7 @@ export default class Trainer extends Phaser.GameObjects.Container {
 
   genPartyMember(index: integer): EnemyPokemon {
     const battle = this.scene.currentBattle;
-    const level = battle.enemyLevels[index];
+    const level = battle.enemyLevels?.[index]!; // TODO: is this bang correct?
 
     let ret: EnemyPokemon;
 
@@ -290,7 +290,7 @@ export default class Trainer extends Phaser.GameObjects.Container {
       }
 
       // Create an empty species pool (which will be set to one of the species pools based on the index)
-      let newSpeciesPool = [];
+      let newSpeciesPool: Species[] = [];
       let useNewSpeciesPool = false;
 
       // If we are in a double battle of named trainers, we need to use alternate species pools (generate half the party from each trainer)
@@ -315,7 +315,7 @@ export default class Trainer extends Phaser.GameObjects.Container {
             return !species.some(s => AlreadyUsedSpecies.includes(s));
           }
           return !AlreadyUsedSpecies.includes(species);
-        });
+        }).flat();
 
         // Filter out the species that are already in the enemy party from the partner trainer species pool
         const speciesPoolPartnerFiltered = speciesPoolPartner.filter(species => {
@@ -324,7 +324,7 @@ export default class Trainer extends Phaser.GameObjects.Container {
             return !species.some(s => AlreadyUsedSpecies.includes(s));
           }
           return !AlreadyUsedSpecies.includes(species);
-        });
+        }).flat();
 
 
         // If the index is even, use the species pool for the main trainer (that way he only uses his own pokemon in battle)
@@ -370,7 +370,7 @@ export default class Trainer extends Phaser.GameObjects.Container {
       ret = this.scene.addEnemyPokemon(species, level, !this.isDouble() || !(index % 2) ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER);
     }, this.config.hasStaticParty ? this.config.getDerivedType() + ((index + 1) << 8) : this.scene.currentBattle.waveIndex + (this.config.getDerivedType() << 10) + (((!this.config.useSameSeedForAllMembers ? index : 0) + 1) << 8));
 
-    return ret;
+    return ret!; // TODO: is this bang correct?
   }
 
 
@@ -481,7 +481,7 @@ export default class Trainer extends Phaser.GameObjects.Container {
     if (maxScorePartyMemberIndexes.length > 1) {
       let rand: integer;
       this.scene.executeWithSeedOffset(() => rand = Utils.randSeedInt(maxScorePartyMemberIndexes.length), this.scene.currentBattle.turn << 2);
-      return maxScorePartyMemberIndexes[rand];
+      return maxScorePartyMemberIndexes[rand!];
     }
 
     return maxScorePartyMemberIndexes[0];
@@ -499,6 +499,9 @@ export default class Trainer extends Phaser.GameObjects.Container {
       return 0.45;
     case PartyMemberStrength.STRONGER:
       return 0.375;
+    default:
+      console.warn("getPartyMemberModifierChanceMultiplier not defined. Using default 0");
+      return 0;
     }
   }
 
diff --git a/src/game-mode.ts b/src/game-mode.ts
index 010cae03e5e..2475cb5cfb4 100644
--- a/src/game-mode.ts
+++ b/src/game-mode.ts
@@ -167,7 +167,7 @@ export class GameMode implements GameModeConfig {
     }
   }
 
-  getOverrideSpecies(waveIndex: integer): PokemonSpecies {
+  getOverrideSpecies(waveIndex: integer): PokemonSpecies | null {
     if (this.isDaily && this.isWaveFinal(waveIndex)) {
       const allFinalBossSpecies = allSpecies.filter(s => (s.subLegendary || s.legendary || s.mythical)
         && s.baseTotal >= 600 && s.speciesId !== Species.ETERNATUS && s.speciesId !== Species.ARCEUS);
@@ -210,7 +210,7 @@ export class GameMode implements GameModeConfig {
      * @returns true if waveIndex is a multiple of 50 in Endless
      */
   isEndlessBoss(waveIndex: integer): boolean {
-    return waveIndex % 50 &&
+    return !!(waveIndex % 50) &&
         (this.modeId === GameModes.ENDLESS || this.modeId === GameModes.SPLICED_ENDLESS);
   }
 
@@ -267,6 +267,8 @@ export class GameMode implements GameModeConfig {
       return 5000;
     case GameModes.DAILY:
       return 2500;
+    default:
+      return 0;
     }
   }
 
diff --git a/src/inputs-controller.ts b/src/inputs-controller.ts
index 834ca233942..331d491b807 100644
--- a/src/inputs-controller.ts
+++ b/src/inputs-controller.ts
@@ -154,7 +154,7 @@ export class InputsController {
     });
 
     if (typeof this.scene.input.gamepad !== "undefined") {
-      this.scene.input.gamepad.on("connected", function (thisGamepad) {
+      this.scene.input.gamepad?.on("connected", function (thisGamepad) {
         if (!thisGamepad) {
           return;
         }
@@ -163,23 +163,23 @@ export class InputsController {
         this.onReconnect(thisGamepad);
       }, this);
 
-      this.scene.input.gamepad.on("disconnected", function (thisGamepad) {
+      this.scene.input.gamepad?.on("disconnected", function (thisGamepad) {
         this.onDisconnect(thisGamepad); // when a gamepad is disconnected
       }, this);
 
       // Check to see if the gamepad has already been setup by the browser
-      this.scene.input.gamepad.refreshPads();
-      if (this.scene.input.gamepad.total) {
+      this.scene.input.gamepad?.refreshPads();
+      if (this.scene.input.gamepad?.total) {
         this.refreshGamepads();
         for (const thisGamepad of this.gamepads) {
           this.scene.input.gamepad.emit("connected", thisGamepad);
         }
       }
 
-      this.scene.input.gamepad.on("down", this.gamepadButtonDown, this);
-      this.scene.input.gamepad.on("up", this.gamepadButtonUp, this);
-      this.scene.input.keyboard.on("keydown", this.keyboardKeyDown, this);
-      this.scene.input.keyboard.on("keyup", this.keyboardKeyUp, this);
+      this.scene.input.gamepad?.on("down", this.gamepadButtonDown, this);
+      this.scene.input.gamepad?.on("up", this.gamepadButtonUp, this);
+      this.scene.input.keyboard?.on("keydown", this.keyboardKeyDown, this);
+      this.scene.input.keyboard?.on("keyup", this.keyboardKeyUp, this);
     }
     this.touchControls = new TouchControl(this.scene);
   }
@@ -338,9 +338,9 @@ export class InputsController {
      */
   refreshGamepads(): void {
     // Sometimes, gamepads are undefined. For some reason.
-    this.gamepads = this.scene.input.gamepad.gamepads.filter(function (el) {
+    this.gamepads = this.scene.input.gamepad?.gamepads.filter(function (el) {
       return el !== null;
-    });
+    })!; // TODO: is this bang correct?
 
     for (const [index, thisGamepad] of this.gamepads.entries()) {
       thisGamepad.index = index; // Overwrite the gamepad index, in case we had undefined gamepads earlier
diff --git a/src/loading-scene.ts b/src/loading-scene.ts
index 5275411055e..c00112318c8 100644
--- a/src/loading-scene.ts
+++ b/src/loading-scene.ts
@@ -453,8 +453,8 @@ export class LoadingScene extends SceneBase {
       // videos do not need to be preloaded
       intro.loadURL("images/intro_dark.mp4", true);
       if (mobile) {
-        intro.video.setAttribute("webkit-playsinline", "webkit-playsinline");
-        intro.video.setAttribute("playsinline", "playsinline");
+        intro.video?.setAttribute("webkit-playsinline", "webkit-playsinline");
+        intro.video?.setAttribute("playsinline", "playsinline");
       }
       intro.play();
     });
diff --git a/src/messages.ts b/src/messages.ts
index 555a6f30ef1..b9bf94802f7 100644
--- a/src/messages.ts
+++ b/src/messages.ts
@@ -7,7 +7,10 @@ import i18next from "i18next";
  * @param pokemon {@linkcode Pokemon} name and battle context will be retrieved from this instance
  * @returns {string} ex: "Wild Gengar", "Ectoplasma sauvage"
  */
-export function getPokemonNameWithAffix(pokemon: Pokemon): string {
+export function getPokemonNameWithAffix(pokemon: Pokemon | undefined): string {
+  if (!pokemon) {
+    return "Missigno";
+  } // TODO: little easter-egg, lol
   switch (pokemon.scene.currentBattle.battleSpec) {
   case BattleSpec.DEFAULT:
     return !pokemon.isPlayer()
diff --git a/src/modifier/modifier-type.ts b/src/modifier/modifier-type.ts
index 6123ecd3b80..a6117d09ffe 100644
--- a/src/modifier/modifier-type.ts
+++ b/src/modifier/modifier-type.ts
@@ -51,13 +51,13 @@ export class ModifierType {
   public group: string;
   public soundName: string;
   public tier: ModifierTier;
-  protected newModifierFunc: NewModifierFunc;
+  protected newModifierFunc: NewModifierFunc | null;
 
-  constructor(localeKey: string, iconImage: string, newModifierFunc: NewModifierFunc, group?: string, soundName?: string) {
-    this.localeKey = localeKey;
-    this.iconImage = iconImage;
-    this.group = group || "";
-    this.soundName = soundName || "restore";
+  constructor(localeKey: string | null, iconImage: string | null, newModifierFunc: NewModifierFunc | null, group?: string, soundName?: string) {
+    this.localeKey = localeKey!; // TODO: is this bang correct?
+    this.iconImage = iconImage!; // TODO: is this bang correct?
+    this.group = group!; // TODO: is this bang correct?
+    this.soundName = soundName ?? "restore";
     this.newModifierFunc = newModifierFunc;
   }
 
@@ -73,7 +73,7 @@ export class ModifierType {
     this.tier = tier;
   }
 
-  getOrInferTier(poolType: ModifierPoolType = ModifierPoolType.PLAYER): ModifierTier {
+  getOrInferTier(poolType: ModifierPoolType = ModifierPoolType.PLAYER): ModifierTier | null {
     if (this.tier) {
       return this.tier;
     }
@@ -111,16 +111,16 @@ export class ModifierType {
   }
 
   withIdFromFunc(func: ModifierTypeFunc): ModifierType {
-    this.id = Object.keys(modifierTypes).find(k => modifierTypes[k] === func);
+    this.id = Object.keys(modifierTypes).find(k => modifierTypes[k] === func)!; // TODO: is this bang correct?
     return this;
   }
 
-  newModifier(...args: any[]): Modifier {
-    return this.newModifierFunc(this, args);
+  newModifier(...args: any[]): Modifier | null {
+    return this.newModifierFunc && this.newModifierFunc(this, args);
   }
 }
 
-type ModifierTypeGeneratorFunc = (party: Pokemon[], pregenArgs?: any[]) => ModifierType;
+type ModifierTypeGeneratorFunc = (party: Pokemon[], pregenArgs?: any[]) => ModifierType | null;
 
 export class ModifierTypeGenerator extends ModifierType {
   private genTypeFunc:  ModifierTypeGeneratorFunc;
@@ -197,7 +197,7 @@ class AddVoucherModifierType extends ModifierType {
 }
 
 export class PokemonModifierType extends ModifierType {
-  public selectFilter: PokemonSelectFilter;
+  public selectFilter: PokemonSelectFilter | undefined;
 
   constructor(localeKey: string, iconImage: string, newModifierFunc: NewModifierFunc, selectFilter?: PokemonSelectFilter, group?: string, soundName?: string) {
     super(localeKey, iconImage, newModifierFunc, group, soundName);
@@ -298,7 +298,7 @@ export class PokemonStatusHealModifierType extends PokemonModifierType {
 }
 
 export abstract class PokemonMoveModifierType extends PokemonModifierType {
-  public moveSelectFilter: PokemonMoveSelectFilter;
+  public moveSelectFilter: PokemonMoveSelectFilter | undefined;
 
   constructor(localeKey: string, iconImage: string, newModifierFunc: NewModifierFunc, selectFilter?: PokemonSelectFilter, moveSelectFilter?: PokemonMoveSelectFilter, group?: string) {
     super(localeKey, iconImage, newModifierFunc, selectFilter, group);
@@ -338,7 +338,7 @@ export class PokemonAllMovePpRestoreModifierType extends PokemonModifierType {
   constructor(localeKey: string, iconImage: string, restorePoints: integer) {
     super(localeKey, iconImage, (_type, args) => new Modifiers.PokemonAllMovePpRestoreModifier(this, (args[0] as PlayerPokemon).id, this.restorePoints),
       (pokemon: PlayerPokemon) => {
-        if (!pokemon.getMoveset().filter(m => m.ppUsed).length) {
+        if (!pokemon.getMoveset().filter(m => m?.ppUsed).length) {
           return PartyUiHandler.NoEffectMessage;
         }
         return null;
@@ -518,7 +518,7 @@ export class AttackTypeBoosterModifierType extends PokemonHeldItemModifierType i
   public boostPercent: integer;
 
   constructor(moveType: Type, boostPercent: integer) {
-    super("", `${getAttackTypeBoosterItemName(moveType).replace(/[ \-]/g, "_").toLowerCase()}`,
+    super("", `${getAttackTypeBoosterItemName(moveType)?.replace(/[ \-]/g, "_").toLowerCase()}`,
       (_type, args) => new Modifiers.AttackTypeBoosterModifier(this, (args[0] as Pokemon).id, moveType, boostPercent));
 
     this.moveType = moveType;
@@ -526,7 +526,7 @@ export class AttackTypeBoosterModifierType extends PokemonHeldItemModifierType i
   }
 
   get name(): string {
-    return i18next.t(`modifierType:AttackTypeBoosterItem.${getAttackTypeBoosterItemName(this.moveType).replace(/[ \-]/g, "_").toLowerCase()}`);
+    return i18next.t(`modifierType:AttackTypeBoosterItem.${getAttackTypeBoosterItemName(this.moveType)?.replace(/[ \-]/g, "_").toLowerCase()}`);
   }
 
   getDescription(scene: BattleScene): string {
@@ -638,7 +638,7 @@ class AllPokemonFullHpRestoreModifierType extends ModifierType {
   constructor(localeKey: string, iconImage: string, descriptionKey?: string, newModifierFunc?: NewModifierFunc) {
     super(localeKey, iconImage, newModifierFunc || ((_type, _args) => new Modifiers.PokemonHpRestoreModifier(this, -1, 0, 100, false)));
 
-    this.descriptionKey = descriptionKey;
+    this.descriptionKey = descriptionKey!; // TODO: is this bang correct?
   }
 
   getDescription(scene: BattleScene): string {
@@ -773,7 +773,7 @@ export class EvolutionItemModifierType extends PokemonModifierType implements Ge
         if (pokemonEvolutions.hasOwnProperty(pokemon.species.speciesId) && pokemonEvolutions[pokemon.species.speciesId].filter(e => e.item === this.evolutionItem
           && (!e.condition || e.condition.predicate(pokemon))).length && (pokemon.getFormKey() !== SpeciesFormKey.GIGANTAMAX)) {
           return null;
-        } else if (pokemon.isFusion() && pokemonEvolutions.hasOwnProperty(pokemon.fusionSpecies.speciesId) && pokemonEvolutions[pokemon.fusionSpecies.speciesId].filter(e => e.item === this.evolutionItem
+        } else if (pokemon.isFusion() && pokemon.fusionSpecies && pokemonEvolutions.hasOwnProperty(pokemon.fusionSpecies.speciesId) && pokemonEvolutions[pokemon.fusionSpecies.speciesId].filter(e => e.item === this.evolutionItem
         && (!e.condition || e.condition.predicate(pokemon))).length && (pokemon.getFusionFormKey() !== SpeciesFormKey.GIGANTAMAX)) {
           return null;
         }
@@ -859,7 +859,7 @@ class AttackTypeBoosterModifierTypeGenerator extends ModifierTypeGenerator {
         return new AttackTypeBoosterModifierType(pregenArgs[0] as Type, 20);
       }
 
-      const attackMoveTypes = party.map(p => p.getMoveset().map(m => m.getMove()).filter(m => m instanceof AttackMove).map(m => m.type)).flat();
+      const attackMoveTypes = party.map(p => p.getMoveset().map(m => m?.getMove()).filter(m => m instanceof AttackMove).map(m => m.type)).flat();
       if (!attackMoveTypes.length) {
         return null;
       }
@@ -868,8 +868,8 @@ class AttackTypeBoosterModifierTypeGenerator extends ModifierTypeGenerator {
       let totalWeight = 0;
       for (const t of attackMoveTypes) {
         if (attackMoveTypeWeights.has(t)) {
-          if (attackMoveTypeWeights.get(t) < 3) {
-            attackMoveTypeWeights.set(t, attackMoveTypeWeights.get(t) + 1);
+          if (attackMoveTypeWeights.get(t)! < 3) { // attackMoveTypeWeights.has(t) was checked before
+            attackMoveTypeWeights.set(t, attackMoveTypeWeights.get(t)! + 1);
           } else {
             continue;
           }
@@ -889,7 +889,7 @@ class AttackTypeBoosterModifierTypeGenerator extends ModifierTypeGenerator {
       let weight = 0;
 
       for (const t of attackMoveTypeWeights.keys()) {
-        const typeWeight = attackMoveTypeWeights.get(t);
+        const typeWeight = attackMoveTypeWeights.get(t)!; // guranteed to be defined
         if (randInt <= weight + typeWeight) {
           type = t;
           break;
@@ -897,7 +897,7 @@ class AttackTypeBoosterModifierTypeGenerator extends ModifierTypeGenerator {
         weight += typeWeight;
       }
 
-      return new AttackTypeBoosterModifierType(type, 20);
+      return new AttackTypeBoosterModifierType(type!, 20);
     });
   }
 }
@@ -930,7 +930,7 @@ class SpeciesStatBoosterModifierTypeGenerator extends ModifierTypeGenerator {
       for (const p of party) {
         const speciesId = p.getSpeciesForm(true).speciesId;
         const fusionSpeciesId = p.isFusion() ? p.getFusionSpeciesForm(true).speciesId : null;
-        const hasFling = p.getMoveset(true).some(m => m.moveId === Moves.FLING);
+        const hasFling = p.getMoveset(true).some(m => m?.moveId === Moves.FLING);
 
         for (const i in values) {
           const checkedSpecies = values[i].species;
@@ -980,7 +980,7 @@ class SpeciesStatBoosterModifierTypeGenerator extends ModifierTypeGenerator {
 class TmModifierTypeGenerator extends ModifierTypeGenerator {
   constructor(tier: ModifierTier) {
     super((party: Pokemon[]) => {
-      const partyMemberCompatibleTms = party.map(p => (p as PlayerPokemon).compatibleTms.filter(tm => !p.moveset.find(m => m.moveId === tm)));
+      const partyMemberCompatibleTms = party.map(p => (p as PlayerPokemon).compatibleTms.filter(tm => !p.moveset.find(m => m?.moveId === tm)));
       const tierUniqueCompatibleTms = partyMemberCompatibleTms.flat().filter(tm => tmPoolTiers[tm] === tier).filter(tm => !allMoves[tm].name.endsWith(" (N)")).filter((tm, i, array) => array.indexOf(tm) === i);
       if (!tierUniqueCompatibleTms.length) {
         return null;
@@ -1003,17 +1003,17 @@ class EvolutionItemModifierTypeGenerator extends ModifierTypeGenerator {
           const evolutions = pokemonEvolutions[p.species.speciesId];
           return evolutions.filter(e => e.item !== EvolutionItem.NONE && (e.evoFormKey === null || (e.preFormKey || "") === p.getFormKey()) && (!e.condition || e.condition.predicate(p)));
         }).flat(),
-        party.filter(p => p.isFusion() && pokemonEvolutions.hasOwnProperty(p.fusionSpecies.speciesId)).map(p => {
-          const evolutions = pokemonEvolutions[p.fusionSpecies.speciesId];
+        party.filter(p => p.isFusion() && p.fusionSpecies && pokemonEvolutions.hasOwnProperty(p.fusionSpecies.speciesId)).map(p => {
+          const evolutions = pokemonEvolutions[p.fusionSpecies!.speciesId];
           return evolutions.filter(e => e.item !== EvolutionItem.NONE && (e.evoFormKey === null || (e.preFormKey || "") === p.getFusionFormKey()) && (!e.condition || e.condition.predicate(p)));
         }).flat()
-      ].flat().flatMap(e => e.item).filter(i => (i > 50) === rare);
+      ].flat().flatMap(e => e.item).filter(i => (!!i && i > 50) === rare);
 
       if (!evolutionItemPool.length) {
         return null;
       }
 
-      return new EvolutionItemModifierType(evolutionItemPool[Utils.randSeedInt(evolutionItemPool.length)]);
+      return new EvolutionItemModifierType(evolutionItemPool[Utils.randSeedInt(evolutionItemPool.length)]!); // TODO: is the bang correct?
     });
   }
 }
@@ -1156,7 +1156,7 @@ class WeightedModifierType {
 
   constructor(modifierTypeFunc: ModifierTypeFunc, weight: integer | WeightedModifierTypeWeightFunc, maxWeight?: integer) {
     this.modifierType = modifierTypeFunc();
-    this.modifierType.id = Object.keys(modifierTypes).find(k => modifierTypes[k] === modifierTypeFunc);
+    this.modifierType.id = Object.keys(modifierTypes).find(k => modifierTypes[k] === modifierTypeFunc)!; // TODO: is this bang correct?
     this.weight = weight;
     this.maxWeight = maxWeight || (!(weight instanceof Function) ? weight : 0);
   }
@@ -1410,7 +1410,7 @@ export const modifierTypes = {
   VOUCHER_PLUS: () => new AddVoucherModifierType(VoucherType.PLUS, 1),
   VOUCHER_PREMIUM: () => new AddVoucherModifierType(VoucherType.PREMIUM, 1),
 
-  GOLDEN_POKEBALL: () => new ModifierType("modifierType:ModifierType.GOLDEN_POKEBALL", "pb_gold", (type, _args) => new Modifiers.ExtraModifierModifier(type), null, "pb_bounce_1"),
+  GOLDEN_POKEBALL: () => new ModifierType("modifierType:ModifierType.GOLDEN_POKEBALL", "pb_gold", (type, _args) => new Modifiers.ExtraModifierModifier(type), undefined, "pb_bounce_1"),
 
   ENEMY_DAMAGE_BOOSTER: () => new ModifierType("modifierType:ModifierType.ENEMY_DAMAGE_BOOSTER", "wl_item_drop", (type, _args) => new Modifiers.EnemyDamageBoosterModifier(type, 5)),
   ENEMY_DAMAGE_REDUCTION: () => new ModifierType("modifierType:ModifierType.ENEMY_DAMAGE_REDUCTION", "wl_guard_spec", (type, _args) => new Modifiers.EnemyDamageReducerModifier(type, 2.5)),
@@ -1451,11 +1451,11 @@ const modifierPool: ModifierPool = {
       return thresholdPartyMemberCount;
     }, 3),
     new WeightedModifierType(modifierTypes.ETHER, (party: Pokemon[]) => {
-      const thresholdPartyMemberCount = Math.min(party.filter(p => p.hp && p.getMoveset().filter(m => m.ppUsed && (m.getMovePp() - m.ppUsed) <= 5).length).length, 3);
+      const thresholdPartyMemberCount = Math.min(party.filter(p => p.hp && p.getMoveset().filter(m => m?.ppUsed && (m.getMovePp() - m.ppUsed) <= 5).length).length, 3);
       return thresholdPartyMemberCount * 3;
     }, 9),
     new WeightedModifierType(modifierTypes.MAX_ETHER, (party: Pokemon[]) => {
-      const thresholdPartyMemberCount = Math.min(party.filter(p => p.hp && p.getMoveset().filter(m => m.ppUsed && (m.getMovePp() - m.ppUsed) <= 5).length).length, 3);
+      const thresholdPartyMemberCount = Math.min(party.filter(p => p.hp && p.getMoveset().filter(m => m?.ppUsed && (m.getMovePp() - m.ppUsed) <= 5).length).length, 3);
       return thresholdPartyMemberCount;
     }, 3),
     new WeightedModifierType(modifierTypes.LURE, 2),
@@ -1471,7 +1471,7 @@ const modifierPool: ModifierPool = {
     new WeightedModifierType(modifierTypes.FULL_HEAL, (party: Pokemon[]) => {
       const statusEffectPartyMemberCount = Math.min(party.filter(p => p.hp && !!p.status && !p.getHeldItems().some(i => {
         if (i instanceof Modifiers.TurnStatusEffectModifier) {
-          return (i as Modifiers.TurnStatusEffectModifier).getStatusEffect() === p.status.effect;
+          return (i as Modifiers.TurnStatusEffectModifier).getStatusEffect() === p.status?.effect;
         }
         return false;
       })).length, 3);
@@ -1499,7 +1499,7 @@ const modifierPool: ModifierPool = {
     new WeightedModifierType(modifierTypes.FULL_RESTORE, (party: Pokemon[]) => {
       const statusEffectPartyMemberCount = Math.min(party.filter(p => p.hp && !!p.status && !p.getHeldItems().some(i => {
         if (i instanceof Modifiers.TurnStatusEffectModifier) {
-          return (i as Modifiers.TurnStatusEffectModifier).getStatusEffect() === p.status.effect;
+          return (i as Modifiers.TurnStatusEffectModifier).getStatusEffect() === p.status?.effect;
         }
         return false;
       })).length, 3);
@@ -1507,11 +1507,11 @@ const modifierPool: ModifierPool = {
       return thresholdPartyMemberCount;
     }, 3),
     new WeightedModifierType(modifierTypes.ELIXIR, (party: Pokemon[]) => {
-      const thresholdPartyMemberCount = Math.min(party.filter(p => p.hp && p.getMoveset().filter(m => m.ppUsed && (m.getMovePp() - m.ppUsed) <= 5).length).length, 3);
+      const thresholdPartyMemberCount = Math.min(party.filter(p => p.hp && p.getMoveset().filter(m => m?.ppUsed && (m.getMovePp() - m.ppUsed) <= 5).length).length, 3);
       return thresholdPartyMemberCount * 3;
     }, 9),
     new WeightedModifierType(modifierTypes.MAX_ELIXIR, (party: Pokemon[]) => {
-      const thresholdPartyMemberCount = Math.min(party.filter(p => p.hp && p.getMoveset().filter(m => m.ppUsed && (m.getMovePp() - m.ppUsed) <= 5).length).length, 3);
+      const thresholdPartyMemberCount = Math.min(party.filter(p => p.hp && p.getMoveset().filter(m => m?.ppUsed && (m.getMovePp() - m.ppUsed) <= 5).length).length, 3);
       return thresholdPartyMemberCount;
     }, 3),
     new WeightedModifierType(modifierTypes.DIRE_HIT, 4),
@@ -1555,19 +1555,19 @@ const modifierPool: ModifierPool = {
       const checkedAbilities = [Abilities.QUICK_FEET, Abilities.GUTS, Abilities.MARVEL_SCALE, Abilities.TOXIC_BOOST, Abilities.POISON_HEAL, Abilities.MAGIC_GUARD];
       const checkedMoves = [Moves.FACADE, Moves.TRICK, Moves.FLING, Moves.SWITCHEROO, Moves.PSYCHO_SHIFT];
       // If a party member doesn't already have one of these two orbs and has one of the above moves or abilities, the orb can appear
-      return party.some(p => !p.getHeldItems().some(i => i instanceof Modifiers.TurnStatusEffectModifier) && (checkedAbilities.some(a => p.hasAbility(a, false, true)) || p.getMoveset(true).some(m => checkedMoves.includes(m.moveId)))) ? 10 : 0;
+      return party.some(p => !p.getHeldItems().some(i => i instanceof Modifiers.TurnStatusEffectModifier) && (checkedAbilities.some(a => p.hasAbility(a, false, true)) || p.getMoveset(true).some(m => m && checkedMoves.includes(m.moveId)))) ? 10 : 0;
     }, 10),
     new WeightedModifierType(modifierTypes.FLAME_ORB, (party: Pokemon[]) => {
       const checkedAbilities = [Abilities.QUICK_FEET, Abilities.GUTS, Abilities.MARVEL_SCALE, Abilities.FLARE_BOOST, Abilities.MAGIC_GUARD];
       const checkedMoves = [Moves.FACADE, Moves.TRICK, Moves.FLING, Moves.SWITCHEROO, Moves.PSYCHO_SHIFT];
       // If a party member doesn't already have one of these two orbs and has one of the above moves or abilities, the orb can appear
-      return party.some(p => !p.getHeldItems().some(i => i instanceof Modifiers.TurnStatusEffectModifier) && (checkedAbilities.some(a => p.hasAbility(a, false, true)) || p.getMoveset(true).some(m => checkedMoves.includes(m.moveId)))) ? 10 : 0;
+      return party.some(p => !p.getHeldItems().some(i => i instanceof Modifiers.TurnStatusEffectModifier) && (checkedAbilities.some(a => p.hasAbility(a, false, true)) || p.getMoveset(true).some(m => m && checkedMoves.includes(m.moveId)))) ? 10 : 0;
     }, 10),
     new WeightedModifierType(modifierTypes.WHITE_HERB, (party: Pokemon[]) => {
       const checkedAbilities = [Abilities.WEAK_ARMOR, Abilities.CONTRARY, Abilities.MOODY, Abilities.ANGER_SHELL, Abilities.COMPETITIVE, Abilities.DEFIANT];
       const weightMultiplier = party.filter(
         p => !p.getHeldItems().some(i => i instanceof Modifiers.PokemonResetNegativeStatStageModifier && i.stackCount >= i.getMaxHeldItemCount(p)) &&
-          (checkedAbilities.some(a => p.hasAbility(a, false, true)) || p.getMoveset(true).some(m => selfStatLowerMoves.includes(m.moveId)))).length;
+          (checkedAbilities.some(a => p.hasAbility(a, false, true)) || p.getMoveset(true).some(m => m && selfStatLowerMoves.includes(m.moveId)))).length;
       // If a party member has one of the above moves or abilities and doesn't have max herbs, the herb will appear more frequently
       return 0 * (weightMultiplier ? 2 : 1) + (weightMultiplier ? weightMultiplier * 0 : 0);
     }, 10),
@@ -1722,10 +1722,10 @@ const enemyBuffModifierPool: ModifierPool = {
   ].map(m => {
     m.setTier(ModifierTier.ULTRA); return m;
   }),
-  [ModifierTier.ROGUE]: [ ].map(m => {
+  [ModifierTier.ROGUE]: [ ].map((m: WeightedModifierType) => {
     m.setTier(ModifierTier.ROGUE); return m;
   }),
-  [ModifierTier.MASTER]: [ ].map(m => {
+  [ModifierTier.MASTER]: [ ].map((m: WeightedModifierType) => {
     m.setTier(ModifierTier.MASTER); return m;
   })
 };
@@ -1770,7 +1770,7 @@ const dailyStarterModifierPool: ModifierPool = {
 export function getModifierType(modifierTypeFunc: ModifierTypeFunc): ModifierType {
   const modifierType = modifierTypeFunc();
   if (!modifierType.id) {
-    modifierType.id = Object.keys(modifierTypes).find(k => modifierTypes[k] === modifierTypeFunc);
+    modifierType.id = Object.keys(modifierTypes).find(k => modifierTypes[k] === modifierTypeFunc)!; // TODO: is this bang correct?
   }
   return modifierType;
 }
@@ -1893,12 +1893,14 @@ export function getPlayerModifierTypeOptions(count: integer, party: PlayerPokemo
   const options: ModifierTypeOption[] = [];
   const retryCount = Math.min(count * 5, 50);
   new Array(count).fill(0).map((_, i) => {
-    let candidate = getNewModifierTypeOption(party, ModifierPoolType.PLAYER, modifierTiers?.length > i ? modifierTiers[i] : undefined);
+    let candidate = getNewModifierTypeOption(party, ModifierPoolType.PLAYER, modifierTiers && modifierTiers.length > i ? modifierTiers[i] : undefined);
     let r = 0;
-    while (options.length && ++r < retryCount && options.filter(o => o.type.name === candidate.type.name || o.type.group === candidate.type.group).length) {
-      candidate = getNewModifierTypeOption(party, ModifierPoolType.PLAYER, candidate.type.tier, candidate.upgradeCount);
+    while (options.length && ++r < retryCount && options.filter(o => o.type?.name === candidate?.type?.name || o.type?.group === candidate?.type?.group).length) {
+      candidate = getNewModifierTypeOption(party, ModifierPoolType.PLAYER, candidate?.type?.tier, candidate?.upgradeCount);
+    }
+    if (candidate) {
+      options.push(candidate);
     }
-    options.push(candidate);
   });
 
   // OVERRIDE IF NECESSARY
@@ -1950,21 +1952,21 @@ export function getPlayerShopModifierTypeOptionsForWave(waveIndex: integer, base
 export function getEnemyBuffModifierForWave(tier: ModifierTier, enemyModifiers: Modifiers.PersistentModifier[], scene: BattleScene): Modifiers.EnemyPersistentModifier {
   const tierStackCount = tier === ModifierTier.ULTRA ? 5 : tier === ModifierTier.GREAT ? 3 : 1;
   const retryCount = 50;
-  let candidate = getNewModifierTypeOption(null, ModifierPoolType.ENEMY_BUFF, tier);
+  let candidate = getNewModifierTypeOption([], ModifierPoolType.ENEMY_BUFF, tier);
   let r = 0;
-  let matchingModifier: Modifiers.PersistentModifier;
-  while (++r < retryCount && (matchingModifier = enemyModifiers.find(m => m.type.id === candidate.type.id)) && matchingModifier.getMaxStackCount(scene) < matchingModifier.stackCount + (r < 10 ? tierStackCount : 1)) {
-    candidate = getNewModifierTypeOption(null, ModifierPoolType.ENEMY_BUFF, tier);
+  let matchingModifier: Modifiers.PersistentModifier | undefined;
+  while (++r < retryCount && (matchingModifier = enemyModifiers.find(m => m.type.id === candidate?.type?.id)) && matchingModifier.getMaxStackCount(scene) < matchingModifier.stackCount + (r < 10 ? tierStackCount : 1)) {
+    candidate = getNewModifierTypeOption([], ModifierPoolType.ENEMY_BUFF, tier);
   }
 
-  const modifier = candidate.type.newModifier() as Modifiers.EnemyPersistentModifier;
+  const modifier = candidate?.type?.newModifier() as Modifiers.EnemyPersistentModifier;
   modifier.stackCount = tierStackCount;
 
   return modifier;
 }
 
 export function getEnemyModifierTypesForWave(waveIndex: integer, count: integer, party: EnemyPokemon[], poolType: ModifierPoolType.WILD | ModifierPoolType.TRAINER, upgradeChance: integer = 0): PokemonHeldItemModifierType[] {
-  const ret = new Array(count).fill(0).map(() => getNewModifierTypeOption(party, poolType, undefined, upgradeChance && !Utils.randSeedInt(upgradeChance) ? 1 : 0).type as PokemonHeldItemModifierType);
+  const ret = new Array(count).fill(0).map(() => getNewModifierTypeOption(party, poolType, undefined, upgradeChance && !Utils.randSeedInt(upgradeChance) ? 1 : 0)?.type as PokemonHeldItemModifierType);
   if (!(waveIndex % 1000)) {
     ret.push(getModifierType(modifierTypes.MINI_BLACK_HOLE) as PokemonHeldItemModifierType);
   }
@@ -1977,7 +1979,7 @@ export function getDailyRunStarterModifiers(party: PlayerPokemon[]): Modifiers.P
     for (let m = 0; m < 3; m++) {
       const tierValue = Utils.randSeedInt(64);
       const tier = tierValue > 25 ? ModifierTier.COMMON : tierValue > 12 ? ModifierTier.GREAT : tierValue > 4 ? ModifierTier.ULTRA : tierValue ? ModifierTier.ROGUE : ModifierTier.MASTER;
-      const modifier = getNewModifierTypeOption(party, ModifierPoolType.DAILY_STARTER, tier).type.newModifier(p) as Modifiers.PokemonHeldItemModifier;
+      const modifier = getNewModifierTypeOption(party, ModifierPoolType.DAILY_STARTER, tier)?.type?.newModifier(p) as Modifiers.PokemonHeldItemModifier;
       ret.push(modifier);
     }
   }
@@ -1985,7 +1987,7 @@ export function getDailyRunStarterModifiers(party: PlayerPokemon[]): Modifiers.P
   return ret;
 }
 
-function getNewModifierTypeOption(party: Pokemon[], poolType: ModifierPoolType, tier?: ModifierTier, upgradeCount?: integer, retryCount: integer = 0): ModifierTypeOption {
+function getNewModifierTypeOption(party: Pokemon[], poolType: ModifierPoolType, tier?: ModifierTier, upgradeCount?: integer, retryCount: integer = 0): ModifierTypeOption | null {
   const player = !poolType;
   const pool = getModifierPoolForType(poolType);
   let thresholds: object;
@@ -2052,7 +2054,7 @@ function getNewModifierTypeOption(party: Pokemon[], poolType: ModifierPoolType,
   const tierThresholds = Object.keys(thresholds[tier]);
   const totalWeight = parseInt(tierThresholds[tierThresholds.length - 1]);
   const value = Utils.randSeedInt(totalWeight);
-  let index: integer;
+  let index: integer | undefined;
   for (const t of tierThresholds) {
     const threshold = parseInt(t);
     if (value < threshold) {
@@ -2068,7 +2070,7 @@ function getNewModifierTypeOption(party: Pokemon[], poolType: ModifierPoolType,
   if (player) {
     console.log(index, ignoredPoolIndexes[tier].filter(i => i <= index).length, ignoredPoolIndexes[tier]);
   }
-  let modifierType: ModifierType = (pool[tier][index]).modifierType;
+  let modifierType: ModifierType | null = (pool[tier][index]).modifierType;
   if (modifierType instanceof ModifierTypeGenerator) {
     modifierType = (modifierType as ModifierTypeGenerator).generateType(party);
     if (modifierType === null) {
@@ -2081,7 +2083,7 @@ function getNewModifierTypeOption(party: Pokemon[], poolType: ModifierPoolType,
 
   console.log(modifierType, !player ? "(enemy)" : "");
 
-  return new ModifierTypeOption(modifierType as ModifierType, upgradeCount);
+  return new ModifierTypeOption(modifierType as ModifierType, upgradeCount!); // TODO: is this bang correct?
 }
 
 export function getDefaultModifierTypeForTier(tier: ModifierTier): ModifierType {
@@ -2093,7 +2095,7 @@ export function getDefaultModifierTypeForTier(tier: ModifierTier): ModifierType
 }
 
 export class ModifierTypeOption {
-  public type: ModifierType;
+  public type: ModifierType | null;
   public upgradeCount: integer;
   public cost: integer;
 
diff --git a/src/modifier/modifier.ts b/src/modifier/modifier.ts
index 91041dc7564..6ff2d3c9718 100644
--- a/src/modifier/modifier.ts
+++ b/src/modifier/modifier.ts
@@ -33,16 +33,16 @@ export type ModifierPredicate = (modifier: Modifier) => boolean;
 
 const iconOverflowIndex = 24;
 
-export const modifierSortFunc = (a: Modifier, b: Modifier) => {
+export const modifierSortFunc = (a: Modifier, b: Modifier): number => {
   const itemNameMatch = a.type.name.localeCompare(b.type.name);
   const typeNameMatch = a.constructor.name.localeCompare(b.constructor.name);
-  const aId = a instanceof PokemonHeldItemModifier ? a.pokemonId : 4294967295;
-  const bId = b instanceof PokemonHeldItemModifier ? b.pokemonId : 4294967295;
+  const aId = a instanceof PokemonHeldItemModifier && a.pokemonId ? a.pokemonId : 4294967295;
+  const bId = b instanceof PokemonHeldItemModifier && b.pokemonId ? b.pokemonId : 4294967295;
 
   //First sort by pokemonID
   if (aId < bId) {
     return 1;
-  } else if (aId>bId) {
+  } else if (aId > bId) {
     return -1;
   } else if (aId === bId) {
     //Then sort by item type
@@ -52,6 +52,8 @@ export const modifierSortFunc = (a: Modifier, b: Modifier) => {
     } else {
       return typeNameMatch;
     }
+  } else {
+    return 0;
   }
 };
 
@@ -150,7 +152,7 @@ export abstract class PersistentModifier extends Modifier {
   public stackCount: integer;
   public virtualStackCount: integer;
 
-  constructor(type: ModifierType, stackCount: integer) {
+  constructor(type: ModifierType, stackCount?: integer) {
     super(type);
     this.stackCount = stackCount === undefined ? 1 : stackCount;
     this.virtualStackCount = 0;
@@ -221,7 +223,7 @@ export abstract class PersistentModifier extends Modifier {
     return container;
   }
 
-  getIconStackText(scene: BattleScene, virtual?: boolean): Phaser.GameObjects.BitmapText {
+  getIconStackText(scene: BattleScene, virtual?: boolean): Phaser.GameObjects.BitmapText | null {
     if (this.getMaxStackCount(scene) === 1 || (virtual && !this.virtualStackCount)) {
       return null;
     }
@@ -295,7 +297,7 @@ export abstract class LapsingPersistentModifier extends PersistentModifier {
   constructor(type: ModifierTypes.ModifierType, battlesLeft?: integer, stackCount?: integer) {
     super(type, stackCount);
 
-    this.battlesLeft = battlesLeft;
+    this.battlesLeft = battlesLeft!; // TODO: is this bang correct?
   }
 
   lapse(args: any[]): boolean {
@@ -306,7 +308,7 @@ export abstract class LapsingPersistentModifier extends PersistentModifier {
     const container = super.getIcon(scene);
 
     const battleCountText = addTextObject(scene, 27, 0, this.battlesLeft.toString(), TextStyle.PARTY, { fontSize: "66px", color: "#f89890" });
-    battleCountText.setShadow(0, 0, null);
+    battleCountText.setShadow(0, 0);
     battleCountText.setStroke("#984038", 16);
     battleCountText.setOrigin(1, 0);
     container.add(battleCountText);
@@ -472,7 +474,7 @@ export abstract class PokemonHeldItemModifier extends PersistentModifier {
   public pokemonId: integer;
   readonly isTransferrable: boolean = true;
 
-  constructor(type: ModifierType, pokemonId: integer, stackCount: integer) {
+  constructor(type: ModifierType, pokemonId: integer, stackCount?: integer) {
     super(type, stackCount);
 
     this.pokemonId = pokemonId;
@@ -489,11 +491,11 @@ export abstract class PokemonHeldItemModifier extends PersistentModifier {
   }
 
   shouldApply(args: any[]): boolean {
-    return super.shouldApply(args) && args.length && args[0] instanceof Pokemon && (this.pokemonId === -1 || (args[0] as Pokemon).id === this.pokemonId);
+    return super.shouldApply(args) && args.length !== 0 && args[0] instanceof Pokemon && (this.pokemonId === -1 || (args[0] as Pokemon).id === this.pokemonId);
   }
 
   isIconVisible(scene: BattleScene): boolean {
-    return this.getPokemon(scene).isOnField();
+    return !!(this.getPokemon(scene)?.isOnField());
   }
 
   getIcon(scene: BattleScene, forSummary?: boolean): Phaser.GameObjects.Container {
@@ -501,9 +503,10 @@ export abstract class PokemonHeldItemModifier extends PersistentModifier {
 
     if (!forSummary) {
       const pokemon = this.getPokemon(scene);
-      const pokemonIcon = scene.addPokemonIcon(pokemon, -2, 10, 0, 0.5);
-
-      container.add(pokemonIcon);
+      if (pokemon) {
+        const pokemonIcon = scene.addPokemonIcon(pokemon, -2, 10, 0, 0.5);
+        container.add(pokemonIcon);
+      }
 
       const item = scene.add.sprite(16, this.virtualStackCount ? 8 : 16, "items");
       item.setScale(0.5);
@@ -527,8 +530,8 @@ export abstract class PokemonHeldItemModifier extends PersistentModifier {
     return container;
   }
 
-  getPokemon(scene: BattleScene): Pokemon {
-    return scene.getPokemonById(this.pokemonId);
+  getPokemon(scene: BattleScene): Pokemon | undefined {
+    return this.pokemonId ? scene.getPokemonById(this.pokemonId) ?? undefined : undefined;
   }
 
   getScoreMultiplier(): number {
@@ -562,7 +565,7 @@ export abstract class PokemonHeldItemModifier extends PersistentModifier {
     return this.getMaxHeldItemCount(pokemon);
   }
 
-  abstract getMaxHeldItemCount(pokemon: Pokemon): integer;
+  abstract getMaxHeldItemCount(pokemon?: Pokemon): integer;
 }
 
 export abstract class LapsingPokemonHeldItemModifier extends PokemonHeldItemModifier {
@@ -572,7 +575,7 @@ export abstract class LapsingPokemonHeldItemModifier extends PokemonHeldItemModi
   constructor(type: ModifierTypes.ModifierType, pokemonId: integer, battlesLeft?: integer, stackCount?: integer) {
     super(type, pokemonId, stackCount);
 
-    this.battlesLeft = battlesLeft;
+    this.battlesLeft = battlesLeft!; // TODO: is this bang correct?
   }
 
   lapse(args: any[]): boolean {
@@ -582,9 +585,9 @@ export abstract class LapsingPokemonHeldItemModifier extends PokemonHeldItemModi
   getIcon(scene: BattleScene, forSummary?: boolean): Phaser.GameObjects.Container {
     const container = super.getIcon(scene, forSummary);
 
-    if (this.getPokemon(scene).isPlayer()) {
+    if (this.getPokemon(scene)?.isPlayer()) {
       const battleCountText = addTextObject(scene, 27, 0, this.battlesLeft.toString(), TextStyle.PARTY, { fontSize: "66px", color: "#f89890" });
-      battleCountText.setShadow(0, 0, null);
+      battleCountText.setShadow(0, 0);
       battleCountText.setStroke("#984038", 16);
       battleCountText.setOrigin(1, 0);
       container.add(battleCountText);
@@ -1442,7 +1445,7 @@ export abstract class ConsumablePokemonModifier extends ConsumableModifier {
   }
 
   shouldApply(args: any[]): boolean {
-    return args.length && args[0] instanceof PlayerPokemon && (this.pokemonId === -1 || (args[0] as PlayerPokemon).id === this.pokemonId);
+    return args.length !== 0 && args[0] instanceof PlayerPokemon && (this.pokemonId === -1 || (args[0] as PlayerPokemon).id === this.pokemonId);
   }
 
   getPokemon(scene: BattleScene) {
@@ -1519,7 +1522,7 @@ export class PokemonPpRestoreModifier extends ConsumablePokemonMoveModifier {
 
   apply(args: any[]): boolean {
     const pokemon = args[0] as Pokemon;
-    const move = pokemon.getMoveset()[this.moveIndex];
+    const move = pokemon.getMoveset()[this.moveIndex]!; //TODO: is the bang correct?
     move.ppUsed = this.restorePoints > -1 ? Math.max(move.ppUsed - this.restorePoints, 0) : 0;
 
     return true;
@@ -1538,7 +1541,7 @@ export class PokemonAllMovePpRestoreModifier extends ConsumablePokemonModifier {
   apply(args: any[]): boolean {
     const pokemon = args[0] as Pokemon;
     for (const move of pokemon.getMoveset()) {
-      move.ppUsed = this.restorePoints > -1 ? Math.max(move.ppUsed - this.restorePoints, 0) : 0;
+      move!.ppUsed = this.restorePoints > -1 ? Math.max(move!.ppUsed - this.restorePoints, 0) : 0; // TODO: are those bangs correct?
     }
 
     return true;
@@ -1556,7 +1559,7 @@ export class PokemonPpUpModifier extends ConsumablePokemonMoveModifier {
 
   apply(args: any[]): boolean {
     const pokemon = args[0] as Pokemon;
-    const move = pokemon.getMoveset()[this.moveIndex];
+    const move = pokemon.getMoveset()[this.moveIndex]!; // TODO: is the bang correct?
     move.ppUp = Math.min(move.ppUp + this.upPoints, 3);
 
     return true;
@@ -1658,7 +1661,7 @@ export class EvolutionItemModifier extends ConsumablePokemonModifier {
       : null;
 
     if (!matchingEvolution && pokemon.isFusion()) {
-      matchingEvolution = pokemonEvolutions[pokemon.fusionSpecies.speciesId].find(e => e.item === (this.type as ModifierTypes.EvolutionItemModifierType).evolutionItem
+      matchingEvolution = pokemonEvolutions[pokemon.fusionSpecies!.speciesId].find(e => e.item === (this.type as ModifierTypes.EvolutionItemModifierType).evolutionItem // TODO: is the bang correct?
         && (e.evoFormKey === null || (e.preFormKey || "") === pokemon.getFusionFormKey())
         && (!e.condition || e.condition.predicate(pokemon)));
       if (matchingEvolution) {
@@ -2135,7 +2138,7 @@ export class MoneyInterestModifier extends PersistentModifier {
     const userLocale = navigator.language || "en-US";
     const formattedMoneyAmount = interestAmount.toLocaleString(userLocale);
     const message = i18next.t("modifier:moneyInterestApply", { moneyAmount: formattedMoneyAmount, typeName: this.type.name });
-    scene.queueMessage(message, null, true);
+    scene.queueMessage(message, undefined, true);
 
     return true;
   }
@@ -2290,7 +2293,7 @@ export abstract class HeldItemTransferModifier extends PokemonHeldItemModifier {
     const transferredModifierTypes: ModifierTypes.ModifierType[] = [];
     const itemModifiers = pokemon.scene.findModifiers(m => m instanceof PokemonHeldItemModifier
         && m.pokemonId === targetPokemon.id && m.isTransferrable, targetPokemon.isPlayer()) as PokemonHeldItemModifier[];
-    let highestItemTier = itemModifiers.map(m => m.type.getOrInferTier(poolType)).reduce((highestTier, tier) => Math.max(tier, highestTier), 0);
+    let highestItemTier = itemModifiers.map(m => m.type.getOrInferTier(poolType)).reduce((highestTier, tier) => Math.max(tier!, highestTier), 0); // TODO: is this bang correct?
     let tierItemModifiers = itemModifiers.filter(m => m.type.getOrInferTier(poolType) === highestItemTier);
 
     const heldItemTransferPromises: Promise<void>[] = [];
@@ -2782,8 +2785,8 @@ export function overrideHeldItems(scene: BattleScene, pokemon: Pokemon, player:
     const modifierType: ModifierType = modifierTypes[itemName](); // we retrieve the item in the list
     let itemModifier: PokemonHeldItemModifier;
     if (modifierType instanceof ModifierTypes.ModifierTypeGenerator) {
-      const pregenArgs = "type" in item ? [item.type] : null;
-      itemModifier = modifierType.generateType(null, pregenArgs).withIdFromFunc(modifierTypes[itemName]).newModifier(pokemon) as PokemonHeldItemModifier;
+      const pregenArgs = "type" in item ? [item.type] : undefined;
+      itemModifier = modifierType.generateType([], pregenArgs)?.withIdFromFunc(modifierTypes[itemName]).newModifier(pokemon) as PokemonHeldItemModifier;
     } else {
       itemModifier = modifierType.withIdFromFunc(modifierTypes[itemName]).newModifier(pokemon) as PokemonHeldItemModifier;
     }
diff --git a/src/overrides.ts b/src/overrides.ts
index 9dd394354aa..88db105475c 100644
--- a/src/overrides.ts
+++ b/src/overrides.ts
@@ -48,9 +48,9 @@ class DefaultOverrides {
   readonly BATTLE_TYPE_OVERRIDE: "double" | "single" | null = null;
   readonly STARTING_WAVE_OVERRIDE: integer = 0;
   readonly STARTING_BIOME_OVERRIDE: Biome = Biome.TOWN;
-  readonly ARENA_TINT_OVERRIDE: TimeOfDay = null;
+  readonly ARENA_TINT_OVERRIDE: TimeOfDay | null = null;
   /** Multiplies XP gained by this value including 0. Set to null to ignore the override */
-  readonly XP_MULTIPLIER_OVERRIDE: number = null;
+  readonly XP_MULTIPLIER_OVERRIDE: number | null = null;
   /** default 1000 */
   readonly STARTING_MONEY_OVERRIDE: integer = 0;
   /** Sets all shop item prices to 0 */
@@ -96,7 +96,7 @@ class DefaultOverrides {
   readonly ABILITY_OVERRIDE: Abilities = Abilities.NONE;
   readonly PASSIVE_ABILITY_OVERRIDE: Abilities = Abilities.NONE;
   readonly STATUS_OVERRIDE: StatusEffect = StatusEffect.NONE;
-  readonly GENDER_OVERRIDE: Gender = null;
+  readonly GENDER_OVERRIDE: Gender | null = null;
   readonly MOVESET_OVERRIDE: Array<Moves> = [];
   readonly SHINY_OVERRIDE: boolean = false;
   readonly VARIANT_OVERRIDE: Variant = 0;
@@ -109,7 +109,7 @@ class DefaultOverrides {
   readonly OPP_ABILITY_OVERRIDE: Abilities = Abilities.NONE;
   readonly OPP_PASSIVE_ABILITY_OVERRIDE: Abilities = Abilities.NONE;
   readonly OPP_STATUS_OVERRIDE: StatusEffect = StatusEffect.NONE;
-  readonly OPP_GENDER_OVERRIDE: Gender = null;
+  readonly OPP_GENDER_OVERRIDE: Gender | null = null;
   readonly OPP_MOVESET_OVERRIDE: Array<Moves> = [];
   readonly OPP_SHINY_OVERRIDE: boolean = false;
   readonly OPP_VARIANT_OVERRIDE: Variant = 0;
@@ -119,9 +119,9 @@ class DefaultOverrides {
   // EGG OVERRIDES
   // -------------
   readonly EGG_IMMEDIATE_HATCH_OVERRIDE: boolean = false;
-  readonly EGG_TIER_OVERRIDE: EggTier = null;
+  readonly EGG_TIER_OVERRIDE: EggTier | null = null;
   readonly EGG_SHINY_OVERRIDE: boolean = false;
-  readonly EGG_VARIANT_OVERRIDE: VariantTier = null;
+  readonly EGG_VARIANT_OVERRIDE: VariantTier | null = null;
   readonly EGG_FREE_GACHA_PULLS_OVERRIDE: boolean = false;
   readonly EGG_GACHA_PULL_COUNT_OVERRIDE: number = 0;
 
diff --git a/src/phases.ts b/src/phases.ts
index f561ea6f3fc..7397974846f 100644
--- a/src/phases.ts
+++ b/src/phases.ts
@@ -194,7 +194,7 @@ export class TitlePhase extends Phase {
 
     this.scene.playBgm("title", true);
 
-    this.scene.gameData.getSession(loggedInUser.lastSessionSlot).then(sessionData => {
+    this.scene.gameData.getSession(loggedInUser!.lastSessionSlot).then(sessionData => { // TODO: is this bang correct?
       if (sessionData) {
         this.lastSessionData = sessionData;
         const biomeKey = getBiomeKey(sessionData.arena.biome);
@@ -210,11 +210,11 @@ export class TitlePhase extends Phase {
 
   showOptions(): void {
     const options: OptionSelectItem[] = [];
-    if (loggedInUser.lastSessionSlot > -1) {
+    if (loggedInUser && loggedInUser.lastSessionSlot > -1) {
       options.push({
-        label: i18next.t("continue", null, { ns: "menu"}),
+        label: i18next.t("continue", {ns: "menu"}),
         handler: () => {
-          this.loadSaveSlot(this.lastSessionData ? -1 : loggedInUser.lastSessionSlot);
+          this.loadSaveSlot(this.lastSessionData || !loggedInUser ? -1 : loggedInUser.lastSessionSlot);
           return true;
         }
       });
@@ -318,9 +318,9 @@ export class TitlePhase extends Phase {
   }
 
   loadSaveSlot(slotId: integer): void {
-    this.scene.sessionSlotId = slotId > -1 ? slotId : loggedInUser.lastSessionSlot;
+    this.scene.sessionSlotId = slotId > -1 || !loggedInUser ? slotId : loggedInUser.lastSessionSlot;
     this.scene.ui.setMode(Mode.MESSAGE);
-    this.scene.gameData.loadSession(this.scene, slotId, slotId === -1 ? this.lastSessionData : null).then((success: boolean) => {
+    this.scene.gameData.loadSession(this.scene, slotId, slotId === -1 ? this.lastSessionData : undefined).then((success: boolean) => {
       if (success) {
         this.loaded = true;
         this.scene.ui.showText(i18next.t("menu:sessionSuccess"), null, () => this.end());
@@ -370,7 +370,8 @@ export class TitlePhase extends Phase {
         regenerateModifierPoolThresholds(party, ModifierPoolType.DAILY_STARTER);
         const modifiers: Modifier[] = Array(3).fill(null).map(() => modifierTypes.EXP_SHARE().withIdFromFunc(modifierTypes.EXP_SHARE).newModifier())
           .concat(Array(3).fill(null).map(() => modifierTypes.GOLDEN_EXP_CHARM().withIdFromFunc(modifierTypes.GOLDEN_EXP_CHARM).newModifier()))
-          .concat(getDailyRunStarterModifiers(party));
+          .concat(getDailyRunStarterModifiers(party))
+          .filter((m) => m !== null);
 
         for (const m of modifiers) {
           this.scene.addModifier(m, true, false, false, true);
@@ -392,7 +393,7 @@ export class TitlePhase extends Phase {
       // If Online, calls seed fetch from db to generate daily run. If Offline, generates a daily run based on current date.
       if (!Utils.isLocal) {
         fetchDailyRunSeed().then(seed => {
-          generateDaily(seed);
+          generateDaily(seed!); // TODO: is this bang correct?
         }).catch(err => {
           console.error("Failed to load daily run:\n", err);
         });
@@ -461,12 +462,12 @@ export class UnavailablePhase extends Phase {
 }
 
 export class ReloadSessionPhase extends Phase {
-  private systemDataStr: string;
+  private systemDataStr: string | null;
 
   constructor(scene: BattleScene, systemDataStr?: string) {
     super(scene);
 
-    this.systemDataStr = systemDataStr;
+    this.systemDataStr = systemDataStr!; // TODO: is this bang correct?
   }
 
   start(): void {
@@ -599,9 +600,9 @@ export class SelectStarterPhase extends Phase {
       let starterFormIndex = Math.min(starterProps.formIndex, Math.max(starter.species.forms.length - 1, 0));
       if (
         starter.species.speciesId in Overrides.STARTER_FORM_OVERRIDES &&
-        starter.species.forms[Overrides.STARTER_FORM_OVERRIDES[starter.species.speciesId]]
+        starter.species.forms[Overrides.STARTER_FORM_OVERRIDES[starter.species.speciesId]!]
       ) {
-        starterFormIndex = Overrides.STARTER_FORM_OVERRIDES[starter.species.speciesId];
+        starterFormIndex = Overrides.STARTER_FORM_OVERRIDES[starter.species.speciesId]!;
       }
 
       let starterGender = starter.species.malePercent !== null
@@ -612,7 +613,7 @@ export class SelectStarterPhase extends Phase {
       }
       const starterIvs = this.scene.gameData.dexData[starter.species.speciesId].ivs.slice(0);
       const starterPokemon = this.scene.addPlayerPokemon(starter.species, this.scene.gameMode.getStartingLevel(), starter.abilityIndex, starterFormIndex, starterGender, starterProps.shiny, starterProps.variant, starterIvs, starter.nature);
-      starterPokemon.tryPopulateMoveset(starter.moveset);
+      starter.moveset && starterPokemon.tryPopulateMoveset(starter.moveset);
       if (starter.passive) {
         starterPokemon.passive = true;
       }
@@ -657,8 +658,8 @@ export class BattlePhase extends Phase {
   }
 
   showEnemyTrainer(trainerSlot: TrainerSlot = TrainerSlot.NONE): void {
-    const sprites = this.scene.currentBattle.trainer.getSprites();
-    const tintSprites = this.scene.currentBattle.trainer.getTintSprites();
+    const sprites = this.scene.currentBattle.trainer?.getSprites()!; // TODO: is this bang correct?
+    const tintSprites = this.scene.currentBattle.trainer?.getTintSprites()!; // TODO: is this bang correct?
     for (let i = 0; i < sprites.length; i++) {
       const visible = !trainerSlot || !i === (trainerSlot === TrainerSlot.TRAINER) || sprites.length < 2;
       [sprites[i], tintSprites[i]].map(sprite => {
@@ -738,11 +739,11 @@ export abstract class PokemonPhase extends FieldPhase {
   public player: boolean;
   public fieldIndex: integer;
 
-  constructor(scene: BattleScene, battlerIndex: BattlerIndex | integer) {
+  constructor(scene: BattleScene, battlerIndex?: BattlerIndex | integer) {
     super(scene);
 
     if (battlerIndex === undefined) {
-      battlerIndex = scene.getField().find(p => p?.isActive()).getBattlerIndex();
+      battlerIndex = scene.getField().find(p => p?.isActive())!.getBattlerIndex(); // TODO: is the bang correct here?
     }
 
     this.battlerIndex = battlerIndex;
@@ -750,11 +751,11 @@ export abstract class PokemonPhase extends FieldPhase {
     this.fieldIndex = battlerIndex % 2;
   }
 
-  getPokemon() {
+  getPokemon(): Pokemon {
     if (this.battlerIndex > BattlerIndex.ENEMY_2) {
-      return this.scene.getPokemonById(this.battlerIndex);
+      return this.scene.getPokemonById(this.battlerIndex)!; //TODO: is this bang correct?
     }
-    return this.scene.getField()[this.battlerIndex];
+    return this.scene.getField()[this.battlerIndex]!; //TODO: is this bang correct?
   }
 }
 
@@ -825,16 +826,16 @@ export class EncounterPhase extends BattlePhase {
       this.scene.unshiftPhase(new GameOverPhase(this.scene));
     }
 
-    const loadEnemyAssets = [];
+    const loadEnemyAssets: Promise<any>[] = [];
 
     const battle = this.scene.currentBattle;
 
     let totalBst = 0;
 
-    battle.enemyLevels.forEach((level, e) => {
+    battle.enemyLevels?.forEach((level, e) => {
       if (!this.loaded) {
         if (battle.battleType === BattleType.TRAINER) {
-          battle.enemyParty[e] = battle.trainer.genPartyMember(e);
+          battle.enemyParty[e] = battle.trainer?.genPartyMember(e)!; // TODO:: is the bang correct here?
         } else {
           const enemySpecies = this.scene.randomSpecies(battle.waveIndex, level, true);
           battle.enemyParty[e] = this.scene.addEnemyPokemon(enemySpecies, level, TrainerSlot.NONE, !!this.scene.getEncounterBossSegments(battle.waveIndex, level, enemySpecies));
@@ -881,7 +882,7 @@ export class EncounterPhase extends BattlePhase {
     }
 
     if (battle.battleType === BattleType.TRAINER) {
-      loadEnemyAssets.push(battle.trainer.loadAssets().then(() => battle.trainer.initSprite()));
+      loadEnemyAssets.push(battle.trainer?.loadAssets().then(() => battle.trainer?.initSprite())!); // TODO: is this bang correct?
     } else {
       // This block only applies for double battles to init the boss segments (idk why it's split up like this)
       if (battle.enemyParty.filter(p => p.isBoss()).length > 1) {
@@ -908,7 +909,7 @@ export class EncounterPhase extends BattlePhase {
             enemyPokemon.tint(0, 0.5);
           } else if (battle.battleType === BattleType.TRAINER) {
             enemyPokemon.setVisible(false);
-            this.scene.currentBattle.trainer.tint(0, 0.5);
+            this.scene.currentBattle.trainer?.tint(0, 0.5);
           }
           if (battle.double) {
             enemyPokemon.setFieldPosition(e ? FieldPosition.RIGHT : FieldPosition.LEFT);
@@ -923,7 +924,8 @@ export class EncounterPhase extends BattlePhase {
 
       this.scene.ui.setMode(Mode.MESSAGE).then(() => {
         if (!this.loaded) {
-          this.scene.gameData.saveAll(this.scene, true, battle.waveIndex % 10 === 1 || this.scene.lastSavePlayTime >= 300).then(success => {
+          //@ts-ignore
+          this.scene.gameData.saveAll(this.scene, true, battle.waveIndex % 10 === 1 || this.scene.lastSavePlayTime >= 300).then(success => { // TODO: get rid of ts-ignore
             this.scene.disableMenu = false;
             if (!success) {
               return this.scene.reset(true);
@@ -980,10 +982,10 @@ export class EncounterPhase extends BattlePhase {
 
     if (this.scene.currentBattle.battleType === BattleType.TRAINER) {
       if (this.scene.currentBattle.double) {
-        return i18next.t("battle:trainerAppearedDouble", { trainerName: this.scene.currentBattle.trainer.getName(TrainerSlot.NONE, true) });
+        return i18next.t("battle:trainerAppearedDouble", { trainerName: this.scene.currentBattle.trainer?.getName(TrainerSlot.NONE, true) });
 
       } else {
-        return i18next.t("battle:trainerAppeared", { trainerName: this.scene.currentBattle.trainer.getName(TrainerSlot.NONE, true) });
+        return i18next.t("battle:trainerAppeared", { trainerName: this.scene.currentBattle.trainer?.getName(TrainerSlot.NONE, true) });
       }
     }
 
@@ -1012,8 +1014,8 @@ export class EncounterPhase extends BattlePhase {
       }
     } else if (this.scene.currentBattle.battleType === BattleType.TRAINER) {
       const trainer = this.scene.currentBattle.trainer;
-      trainer.untint(100, "Sine.easeOut");
-      trainer.playAnim();
+      trainer?.untint(100, "Sine.easeOut");
+      trainer?.playAnim();
 
       const doSummon = () => {
         this.scene.currentBattle.started = true;
@@ -1036,21 +1038,21 @@ export class EncounterPhase extends BattlePhase {
         }
       };
 
-      const encounterMessages = this.scene.currentBattle.trainer.getEncounterMessages();
+      const encounterMessages = this.scene.currentBattle.trainer?.getEncounterMessages();
 
       if (!encounterMessages?.length) {
         doSummon();
       } else {
         let message: string;
         this.scene.executeWithSeedOffset(() => message = Utils.randSeedItem(encounterMessages), this.scene.currentBattle.waveIndex);
-
+        message = message!; // tell TS compiler it's defined now
         const showDialogueAndSummon = () => {
-          this.scene.ui.showDialogue(message, trainer.getName(TrainerSlot.NONE, true), null, () => {
+          this.scene.ui.showDialogue(message, trainer?.getName(TrainerSlot.NONE, true), null, () => {
             this.scene.charSprite.hide().then(() => this.scene.hideFieldOverlay(250).then(() => doSummon()));
           });
         };
-        if (this.scene.currentBattle.trainer.config.hasCharSprite && !this.scene.ui.shouldSkipDialogue(message)) {
-          this.scene.showFieldOverlay(500).then(() => this.scene.charSprite.showCharacter(trainer.getKey(), getCharVariantFromDialogue(encounterMessages[0])).then(() => showDialogueAndSummon()));
+        if (this.scene.currentBattle.trainer?.config.hasCharSprite && !this.scene.ui.shouldSkipDialogue(message)) {
+          this.scene.showFieldOverlay(500).then(() => this.scene.charSprite.showCharacter(trainer?.getKey()!, getCharVariantFromDialogue(encounterMessages[0])).then(() => showDialogueAndSummon())); // TODO: is this bang correct?
         } else {
           showDialogueAndSummon();
         }
@@ -1128,7 +1130,7 @@ export class EncounterPhase extends BattlePhase {
     case BattleSpec.FINAL_BOSS:
       const enemy = this.scene.getEnemyPokemon();
       this.scene.ui.showText(this.getEncounterMessage(), null, () => {
-        this.scene.ui.showDialogue(battleSpecDialogue[BattleSpec.FINAL_BOSS].encounter, enemy.species.name, null, () => {
+        this.scene.ui.showDialogue(battleSpecDialogue[BattleSpec.FINAL_BOSS].encounter, enemy?.species.name, null, () => {
           this.doEncounterCommon(false);
         });
       }, 1500, true);
@@ -1261,14 +1263,14 @@ export class SelectBiomePhase extends BattlePhase {
     } else if (this.scene.gameMode.hasRandomBiomes) {
       setNextBiome(this.generateNextBiome());
     } else if (Array.isArray(biomeLinks[currentBiome])) {
-      let biomes: Biome[];
+      let biomes: Biome[] = [];
       this.scene.executeWithSeedOffset(() => {
         biomes = (biomeLinks[currentBiome] as (Biome | [Biome, integer])[])
           .filter(b => !Array.isArray(b) || !Utils.randSeedInt(b[1]))
           .map(b => !Array.isArray(b) ? b : b[0]);
       }, this.scene.currentBattle.waveIndex);
       if (biomes.length > 1 && this.scene.findModifier(m => m instanceof MapModifier)) {
-        let biomeChoices: Biome[];
+        let biomeChoices: Biome[] = [];
         this.scene.executeWithSeedOffset(() => {
           biomeChoices = (!Array.isArray(biomeLinks[currentBiome])
             ? [biomeLinks[currentBiome] as Biome]
@@ -1437,7 +1439,7 @@ export class SummonPhase extends PartyMemberPokemonPhase {
       });
       this.scene.time.delayedCall(750, () => this.summon());
     } else {
-      const trainerName = this.scene.currentBattle.trainer.getName(!(this.fieldIndex % 2) ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER);
+      const trainerName = this.scene.currentBattle.trainer?.getName(!(this.fieldIndex % 2) ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER);
       const pokemonName = this.getPokemon().getNameToRender();
       const message = i18next.t("battle:trainerSendOut", { trainerName, pokemonName });
 
@@ -1581,7 +1583,8 @@ export class SwitchSummonPhase extends SummonPhase {
   preSummon(): void {
     if (!this.player) {
       if (this.slotIndex === -1) {
-        this.slotIndex = this.scene.currentBattle.trainer.getNextSummonIndex(!this.fieldIndex ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER);
+        //@ts-ignore
+        this.slotIndex = this.scene.currentBattle.trainer?.getNextSummonIndex(!this.fieldIndex ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER); // TODO: what would be the default trainer-slot fallback?
       }
       if (this.slotIndex > -1) {
         this.showEnemyTrainer(!(this.fieldIndex % 2) ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER);
@@ -1607,7 +1610,7 @@ export class SwitchSummonPhase extends SummonPhase {
     this.scene.ui.showText(this.player ?
       i18next.t("battle:playerComeBack", { pokemonName: getPokemonNameWithAffix(pokemon) }) :
       i18next.t("battle:trainerComeBack", {
-        trainerName: this.scene.currentBattle.trainer.getName(!(this.fieldIndex % 2) ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER),
+        trainerName: this.scene.currentBattle.trainer?.getName(!(this.fieldIndex % 2) ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER),
         pokemonName: getPokemonNameWithAffix(pokemon)
       })
     );
@@ -1650,7 +1653,7 @@ export class SwitchSummonPhase extends SummonPhase {
         this.scene.ui.showText(this.player ?
           i18next.t("battle:playerGo", { pokemonName: getPokemonNameWithAffix(switchedInPokemon) }) :
           i18next.t("battle:trainerGo", {
-            trainerName: this.scene.currentBattle.trainer.getName(!(this.fieldIndex % 2) ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER),
+            trainerName: this.scene.currentBattle.trainer?.getName(!(this.fieldIndex % 2) ? TrainerSlot.TRAINER : TrainerSlot.TRAINER_PARTNER),
             pokemonName: this.getPokemon().getNameToRender()
           })
         );
@@ -1929,8 +1932,8 @@ export class CommandPhase extends FieldPhase {
         this.fieldIndex = FieldPosition.CENTER;
       } else {
         const allyCommand = this.scene.currentBattle.turnCommands[this.fieldIndex - 1];
-        if (allyCommand.command === Command.BALL || allyCommand.command === Command.RUN) {
-          this.scene.currentBattle.turnCommands[this.fieldIndex] = { command: allyCommand.command, skip: true };
+        if (allyCommand?.command === Command.BALL || allyCommand?.command === Command.RUN) {
+          this.scene.currentBattle.turnCommands[this.fieldIndex] = { command: allyCommand?.command, skip: true };
         }
       }
     }
@@ -1944,8 +1947,8 @@ export class CommandPhase extends FieldPhase {
     const moveQueue = playerPokemon.getMoveQueue();
 
     while (moveQueue.length && moveQueue[0]
-      && moveQueue[0].move && (!playerPokemon.getMoveset().find(m => m.moveId === moveQueue[0].move)
-        || !playerPokemon.getMoveset()[playerPokemon.getMoveset().findIndex(m => m.moveId === moveQueue[0].move)].isUsable(playerPokemon, moveQueue[0].ignorePP))) {
+      && moveQueue[0].move && (!playerPokemon.getMoveset().find(m => m?.moveId === moveQueue[0].move)
+        || !playerPokemon.getMoveset()[playerPokemon.getMoveset().findIndex(m => m?.moveId === moveQueue[0].move)]!.isUsable(playerPokemon, moveQueue[0].ignorePP))) { // TODO: is the bang correct?
       moveQueue.shift();
     }
 
@@ -1954,8 +1957,8 @@ export class CommandPhase extends FieldPhase {
       if (!queuedMove.move) {
         this.handleCommand(Command.FIGHT, -1, false);
       } else {
-        const moveIndex = playerPokemon.getMoveset().findIndex(m => m.moveId === queuedMove.move);
-        if (moveIndex > -1 && playerPokemon.getMoveset()[moveIndex].isUsable(playerPokemon, queuedMove.ignorePP)) {
+        const moveIndex = playerPokemon.getMoveset().findIndex(m => m?.moveId === queuedMove.move);
+        if (moveIndex > -1 && playerPokemon.getMoveset()[moveIndex]!.isUsable(playerPokemon, queuedMove.ignorePP)) { // TODO: is the bang correct?
           this.handleCommand(Command.FIGHT, moveIndex, queuedMove.ignorePP, { targets: queuedMove.targets, multiple: queuedMove.targets.length > 1 });
         } else {
           this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
@@ -1976,8 +1979,8 @@ export class CommandPhase extends FieldPhase {
       let useStruggle = false;
       if (cursor === -1 ||
           playerPokemon.trySelectMove(cursor, args[0] as boolean) ||
-          (useStruggle = cursor > -1 && !playerPokemon.getMoveset().filter(m => m.isUsable(playerPokemon)).length)) {
-        const moveId = !useStruggle ? cursor > -1 ? playerPokemon.getMoveset()[cursor].moveId : Moves.NONE : Moves.STRUGGLE;
+          (useStruggle = cursor > -1 && !playerPokemon.getMoveset().filter(m => m?.isUsable(playerPokemon)).length)) {
+        const moveId = !useStruggle ? cursor > -1 ? playerPokemon.getMoveset()[cursor]!.moveId : Moves.NONE : Moves.STRUGGLE; // TODO: is the bang correct?
         const turnCommand: TurnCommand = { command: Command.FIGHT, cursor: cursor, move: { move: moveId, targets: [], ignorePP: args[0] }, args: args };
         const moveTargets: MoveTargetSet = args.length < 3 ? getMoveTargets(playerPokemon, moveId) : args[2];
         if (!moveId) {
@@ -1988,16 +1991,16 @@ export class CommandPhase extends FieldPhase {
           this.scene.unshiftPhase(new SelectTargetPhase(this.scene, this.fieldIndex));
         }
         if (moveTargets.targets.length <= 1 || moveTargets.multiple) {
-          turnCommand.move.targets = moveTargets.targets;
+          turnCommand.move!.targets = moveTargets.targets; //TODO: is the bang correct here?
         } else if (playerPokemon.getTag(BattlerTagType.CHARGING) && playerPokemon.getMoveQueue().length >= 1) {
-          turnCommand.move.targets = playerPokemon.getMoveQueue()[0].targets;
+          turnCommand.move!.targets = playerPokemon.getMoveQueue()[0].targets; //TODO: is the bang correct here?
         } else {
           this.scene.unshiftPhase(new SelectTargetPhase(this.scene, this.fieldIndex));
         }
         this.scene.currentBattle.turnCommands[this.fieldIndex] = turnCommand;
         success = true;
       } else if (cursor < playerPokemon.getMoveset().length) {
-        const move = playerPokemon.getMoveset()[cursor];
+        const move = playerPokemon.getMoveset()[cursor]!; //TODO: is this bang correct?
         this.scene.ui.setMode(Mode.MESSAGE);
 
         // Decides between a Disabled, Not Implemented, or No PP translation message
@@ -2017,14 +2020,14 @@ export class CommandPhase extends FieldPhase {
         this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
         this.scene.ui.setMode(Mode.MESSAGE);
         this.scene.ui.showText(i18next.t("battle:noPokeballForce"), null, () => {
-          this.scene.ui.showText(null, 0);
+          this.scene.ui.showText("", 0);
           this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
         }, null, true);
       } else if (this.scene.currentBattle.battleType === BattleType.TRAINER) {
         this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
         this.scene.ui.setMode(Mode.MESSAGE);
         this.scene.ui.showText(i18next.t("battle:noPokeballTrainer"), null, () => {
-          this.scene.ui.showText(null, 0);
+          this.scene.ui.showText("", 0);
           this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
         }, null, true);
       } else {
@@ -2033,23 +2036,23 @@ export class CommandPhase extends FieldPhase {
           this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
           this.scene.ui.setMode(Mode.MESSAGE);
           this.scene.ui.showText(i18next.t("battle:noPokeballMulti"), null, () => {
-            this.scene.ui.showText(null, 0);
+            this.scene.ui.showText("", 0);
             this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
           }, null, true);
         } else if (cursor < 5) {
           const targetPokemon = this.scene.getEnemyField().find(p => p.isActive(true));
-          if (targetPokemon.isBoss() && targetPokemon.bossSegmentIndex >= 1 && !targetPokemon.hasAbility(Abilities.WONDER_GUARD, false, true) && cursor < PokeballType.MASTER_BALL) {
+          if (targetPokemon?.isBoss() && targetPokemon?.bossSegmentIndex >= 1 && !targetPokemon?.hasAbility(Abilities.WONDER_GUARD, false, true) && cursor < PokeballType.MASTER_BALL) {
             this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
             this.scene.ui.setMode(Mode.MESSAGE);
             this.scene.ui.showText(i18next.t("battle:noPokeballStrong"), null, () => {
-              this.scene.ui.showText(null, 0);
+              this.scene.ui.showText("", 0);
               this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
             }, null, true);
           } else {
             this.scene.currentBattle.turnCommands[this.fieldIndex] = { command: Command.BALL, cursor: cursor };
-            this.scene.currentBattle.turnCommands[this.fieldIndex].targets = targets;
+            this.scene.currentBattle.turnCommands[this.fieldIndex]!.targets = targets;
             if (this.fieldIndex) {
-              this.scene.currentBattle.turnCommands[this.fieldIndex - 1].skip = true;
+              this.scene.currentBattle.turnCommands[this.fieldIndex - 1]!.skip = true;
             }
             success = true;
           }
@@ -2063,14 +2066,14 @@ export class CommandPhase extends FieldPhase {
         this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
         this.scene.ui.setMode(Mode.MESSAGE);
         this.scene.ui.showText(i18next.t("battle:noEscapeForce"), null, () => {
-          this.scene.ui.showText(null, 0);
+          this.scene.ui.showText("", 0);
           this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
         }, null, true);
       } else if (!isSwitch && this.scene.currentBattle.battleType === BattleType.TRAINER) {
         this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
         this.scene.ui.setMode(Mode.MESSAGE);
         this.scene.ui.showText(i18next.t("battle:noEscapeTrainer"), null, () => {
-          this.scene.ui.showText(null, 0);
+          this.scene.ui.showText("", 0);
           this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
         }, null, true);
       } else {
@@ -2086,10 +2089,10 @@ export class CommandPhase extends FieldPhase {
             : { command: Command.RUN };
           success = true;
           if (!isSwitch && this.fieldIndex) {
-            this.scene.currentBattle.turnCommands[this.fieldIndex - 1].skip = true;
+            this.scene.currentBattle.turnCommands[this.fieldIndex - 1]!.skip = true;
           }
         } else if (trapTag) {
-          if (trapTag.sourceMove === Moves.INGRAIN && this.scene.getPokemonById(trapTag.sourceId).isOfType(Type.GHOST)) {
+          if (trapTag.sourceMove === Moves.INGRAIN && trapTag.sourceId && this.scene.getPokemonById(trapTag.sourceId)?.isOfType(Type.GHOST)) {
             success = true;
             this.scene.currentBattle.turnCommands[this.fieldIndex] = isSwitch
               ? { command: Command.POKEMON, cursor: cursor, args: args }
@@ -2102,13 +2105,13 @@ export class CommandPhase extends FieldPhase {
           }
           this.scene.ui.showText(
             i18next.t("battle:noEscapePokemon", {
-              pokemonName: getPokemonNameWithAffix(this.scene.getPokemonById(trapTag.sourceId)),
+              pokemonName:  trapTag.sourceId && this.scene.getPokemonById(trapTag.sourceId) ? getPokemonNameWithAffix(this.scene.getPokemonById(trapTag.sourceId)!) : "",
               moveName: trapTag.getMoveName(),
               escapeVerb: isSwitch ? i18next.t("battle:escapeVerbSwitch") : i18next.t("battle:escapeVerbFlee")
             }),
             null,
             () => {
-              this.scene.ui.showText(null, 0);
+              this.scene.ui.showText("", 0);
               if (!isSwitch) {
                 this.scene.ui.setMode(Mode.COMMAND, this.fieldIndex);
               }
@@ -2118,11 +2121,11 @@ export class CommandPhase extends FieldPhase {
       break;
     }
 
-    if (success) {
+    if (success!) { // TODO: is the bang correct?
       this.end();
     }
 
-    return success;
+    return success!; // TODO: is the bang correct?
   }
 
   cancel() {
@@ -2142,9 +2145,9 @@ export class CommandPhase extends FieldPhase {
       return false;
     }
 
-    const moveIndex = pokemon.getMoveset().findIndex(m => m.moveId === encoreTag.moveId);
+    const moveIndex = pokemon.getMoveset().findIndex(m => m?.moveId === encoreTag.moveId);
 
-    if (moveIndex === -1 || !pokemon.getMoveset()[moveIndex].isUsable(pokemon)) {
+    if (moveIndex === -1 || !pokemon.getMoveset()[moveIndex]!.isUsable(pokemon)) { // TODO: is this bang correct?
       return false;
     }
 
@@ -2254,17 +2257,17 @@ export class SelectTargetPhase extends PokemonPhase {
     super.start();
 
     const turnCommand = this.scene.currentBattle.turnCommands[this.fieldIndex];
-    const move = turnCommand.move?.move;
+    const move = turnCommand?.move?.move;
     this.scene.ui.setMode(Mode.TARGET_SELECT, this.fieldIndex, move, (targets: BattlerIndex[]) => {
       this.scene.ui.setMode(Mode.MESSAGE);
       if (targets.length < 1) {
         this.scene.currentBattle.turnCommands[this.fieldIndex] = null;
         this.scene.unshiftPhase(new CommandPhase(this.scene, this.fieldIndex));
       } else {
-        turnCommand.targets = targets;
+        turnCommand!.targets = targets; //TODO: is the bang correct here?
       }
-      if (turnCommand.command === Command.BALL && this.fieldIndex) {
-        this.scene.currentBattle.turnCommands[this.fieldIndex - 1].skip = true;
+      if (turnCommand?.command === Command.BALL && this.fieldIndex) {
+        this.scene.currentBattle.turnCommands[this.fieldIndex - 1]!.skip = true; //TODO: is the bang correct here?
       }
       this.end();
     });
@@ -2297,24 +2300,24 @@ export class TurnStartPhase extends FieldPhase {
       const aCommand = this.scene.currentBattle.turnCommands[a];
       const bCommand = this.scene.currentBattle.turnCommands[b];
 
-      if (aCommand.command !== bCommand.command) {
-        if (aCommand.command === Command.FIGHT) {
+      if (aCommand?.command !== bCommand?.command) {
+        if (aCommand?.command === Command.FIGHT) {
           return 1;
-        } else if (bCommand.command === Command.FIGHT) {
+        } else if (bCommand?.command === Command.FIGHT) {
           return -1;
         }
-      } else if (aCommand.command === Command.FIGHT) {
-        const aMove = allMoves[aCommand.move.move];
-        const bMove = allMoves[bCommand.move.move];
+      } else if (aCommand?.command === Command.FIGHT) {
+        const aMove = allMoves[aCommand.move!.move];//TODO: is the bang correct here?
+        const bMove = allMoves[bCommand!.move!.move];//TODO: is the bang correct here?
 
         const aPriority = new Utils.IntegerHolder(aMove.priority);
         const bPriority = new Utils.IntegerHolder(bMove.priority);
 
-        applyMoveAttrs(IncrementMovePriorityAttr, this.scene.getField().find(p => p?.isActive() && p.getBattlerIndex() === a), null, aMove, aPriority);
-        applyMoveAttrs(IncrementMovePriorityAttr, this.scene.getField().find(p => p?.isActive() && p.getBattlerIndex() === b), null, bMove, bPriority);
+        applyMoveAttrs(IncrementMovePriorityAttr, this.scene.getField().find(p => p?.isActive() && p.getBattlerIndex() === a)!, null, aMove, aPriority); //TODO: is the bang correct here?
+        applyMoveAttrs(IncrementMovePriorityAttr, this.scene.getField().find(p => p?.isActive() && p.getBattlerIndex() === b)!, null, bMove, bPriority); //TODO: is the bang correct here?
 
-        applyAbAttrs(IncrementMovePriorityAbAttr, this.scene.getField().find(p => p?.isActive() && p.getBattlerIndex() === a), null, aMove, aPriority);
-        applyAbAttrs(IncrementMovePriorityAbAttr, this.scene.getField().find(p => p?.isActive() && p.getBattlerIndex() === b), null, bMove, bPriority);
+        applyAbAttrs(IncrementMovePriorityAbAttr, this.scene.getField().find(p => p?.isActive() && p.getBattlerIndex() === a)!, null, aMove, aPriority); //TODO: is the bang correct here?
+        applyAbAttrs(IncrementMovePriorityAbAttr, this.scene.getField().find(p => p?.isActive() && p.getBattlerIndex() === b)!, null, bMove, bPriority); //TODO: is the bang correct here?
 
         if (aPriority.value !== bPriority.value) {
           return aPriority.value < bPriority.value ? 1 : -1;
@@ -2338,34 +2341,34 @@ export class TurnStartPhase extends FieldPhase {
       const pokemon = field[o];
       const turnCommand = this.scene.currentBattle.turnCommands[o];
 
-      if (turnCommand.skip) {
+      if (turnCommand?.skip) {
         continue;
       }
 
-      switch (turnCommand.command) {
+      switch (turnCommand?.command) {
       case Command.FIGHT:
         const queuedMove = turnCommand.move;
         pokemon.turnData.order = orderIndex++;
         if (!queuedMove) {
           continue;
         }
-        const move = pokemon.getMoveset().find(m => m.moveId === queuedMove.move) || new PokemonMove(queuedMove.move);
+        const move = pokemon.getMoveset().find(m => m?.moveId === queuedMove.move) || new PokemonMove(queuedMove.move);
         if (pokemon.isPlayer()) {
           if (turnCommand.cursor === -1) {
-            this.scene.pushPhase(new MovePhase(this.scene, pokemon, turnCommand.targets || turnCommand.move.targets, move));
+            this.scene.pushPhase(new MovePhase(this.scene, pokemon, turnCommand.targets || turnCommand.move!.targets, move));//TODO: is the bang correct here?
           } else {
-            const playerPhase = new MovePhase(this.scene, pokemon, turnCommand.targets || turnCommand.move.targets, move, false, queuedMove.ignorePP);
+            const playerPhase = new MovePhase(this.scene, pokemon, turnCommand.targets || turnCommand.move!.targets, move, false, queuedMove.ignorePP);//TODO: is the bang correct here?
             this.scene.pushPhase(playerPhase);
           }
         } else {
-          this.scene.pushPhase(new MovePhase(this.scene, pokemon, turnCommand.targets || turnCommand.move.targets, move, false, queuedMove.ignorePP));
+          this.scene.pushPhase(new MovePhase(this.scene, pokemon, turnCommand.targets || turnCommand.move!.targets, move, false, queuedMove.ignorePP));//TODO: is the bang correct here?
         }
         break;
       case Command.BALL:
-        this.scene.unshiftPhase(new AttemptCapturePhase(this.scene, turnCommand.targets[0] % 2, turnCommand.cursor));
+        this.scene.unshiftPhase(new AttemptCapturePhase(this.scene, turnCommand.targets![0] % 2, turnCommand.cursor!));//TODO: is the bang correct here?
         break;
       case Command.POKEMON:
-        this.scene.unshiftPhase(new SwitchSummonPhase(this.scene, pokemon.getFieldIndex(), turnCommand.cursor, true, turnCommand.args[0] as boolean, pokemon.isPlayer()));
+        this.scene.unshiftPhase(new SwitchSummonPhase(this.scene, pokemon.getFieldIndex(), turnCommand.cursor!, true, turnCommand.args![0] as boolean, pokemon.isPlayer()));//TODO: is the bang correct here?
         break;
       case Command.RUN:
         let runningPokemon = pokemon;
@@ -2573,13 +2576,13 @@ export class NewBattlePhase extends BattlePhase {
 }
 
 export class CommonAnimPhase extends PokemonPhase {
-  private anim: CommonAnim;
-  private targetIndex: integer;
+  private anim: CommonAnim | null;
+  private targetIndex: integer | undefined;
 
-  constructor(scene: BattleScene, battlerIndex: BattlerIndex, targetIndex: BattlerIndex, anim: CommonAnim) {
+  constructor(scene: BattleScene, battlerIndex?: BattlerIndex, targetIndex?: BattlerIndex | undefined, anim?: CommonAnim) {
     super(scene, battlerIndex);
 
-    this.anim = anim;
+    this.anim = anim!; // TODO: is this bang correct?
     this.targetIndex = targetIndex;
   }
 
@@ -2651,8 +2654,8 @@ export class MovePhase extends BattlePhase {
         this.scene.arena.setIgnoreAbilities();
       }
     } else {
-      this.pokemon.turnData.hitsLeft = undefined;
-      this.pokemon.turnData.hitCount = undefined;
+      this.pokemon.turnData.hitsLeft = 0; // TODO: is `0` correct?
+      this.pokemon.turnData.hitCount = 0; // TODO: is `0` correct?
     }
 
     // Move redirection abilities (ie. Storm Drain) only support single target moves
@@ -2690,7 +2693,8 @@ export class MovePhase extends BattlePhase {
         if (this.scene.currentBattle.double && this.move.getMove().hasFlag(MoveFlags.REDIRECT_COUNTER)) {
           if (this.scene.getField()[this.targets[0]].hp === 0) {
             const opposingField = this.pokemon.isPlayer() ? this.scene.getEnemyField() : this.scene.getPlayerField();
-            this.targets[0] = opposingField.find(p => p.hp > 0)?.getBattlerIndex();
+            //@ts-ignore
+            this.targets[0] = opposingField.find(p => p.hp > 0)?.getBattlerIndex(); //TODO: fix ts-ignore
           }
         }
       }
@@ -2764,7 +2768,7 @@ export class MovePhase extends BattlePhase {
         return this.end();
       }
 
-      if (!moveQueue.length || !moveQueue.shift().ignorePP) { // using .shift here clears out two turn moves once they've been used
+      if (!moveQueue.length || !moveQueue.shift()?.ignorePP) { // using .shift here clears out two turn moves once they've been used
         this.move.usePp(ppUsed);
         this.scene.eventTarget.dispatchEvent(new MoveUsedEvent(this.pokemon?.id, this.move.getMove(), this.move.ppUsed));
       }
@@ -2782,7 +2786,7 @@ export class MovePhase extends BattlePhase {
       } else if (success && this.scene.arena.isMoveTerrainCancelled(this.pokemon, this.targets, this.move.getMove())) {
         success = false;
         if (failedText === null) {
-          failedText = getTerrainBlockMessage(targets[0], this.scene.arena.terrain.terrainType);
+          failedText = getTerrainBlockMessage(targets[0], this.scene.arena.terrain?.terrainType!); // TODO: is this bang correct?
         }
       }
 
@@ -2882,10 +2886,10 @@ export class MovePhase extends BattlePhase {
       pokemonNameWithAffix: getPokemonNameWithAffix(this.pokemon),
       moveName: this.move.getName()
     }), 500);
-    applyMoveAttrs(PreMoveMessageAttr, this.pokemon, this.pokemon.getOpponents().find(() => true), this.move.getMove());
+    applyMoveAttrs(PreMoveMessageAttr, this.pokemon, this.pokemon.getOpponents().find(() => true)!, this.move.getMove()); //TODO: is the bang correct here?
   }
 
-  showFailedText(failedText: string = null): void {
+  showFailedText(failedText: string | null = null): void {
     this.scene.queueMessage(failedText || i18next.t("battle:attackFailed"));
   }
 
@@ -2929,7 +2933,7 @@ export class MoveEffectPhase extends PokemonPhase {
     const move = this.move.getMove();
 
     // Assume single target for override
-    applyMoveAttrs(OverrideMoveEffectAttr, user, this.getTarget(), move, overridden, this.move.virtual).then(() => {
+    applyMoveAttrs(OverrideMoveEffectAttr, user, this.getTarget() ?? null, move, overridden, this.move.virtual).then(() => {
 
       if (overridden.value) {
         return this.end();
@@ -2940,7 +2944,7 @@ export class MoveEffectPhase extends PokemonPhase {
       if (user.turnData.hitsLeft === undefined) {
         const hitCount = new Utils.IntegerHolder(1);
         // Assume single target for multi hit
-        applyMoveAttrs(MultiHitAttr, user, this.getTarget(), move, hitCount);
+        applyMoveAttrs(MultiHitAttr, user, this.getTarget() ?? null, move, hitCount);
         applyPreAttackAbAttrs(AddSecondStrikeAbAttr, user, null, move, targets.length, hitCount, new Utils.IntegerHolder(0));
         if (move instanceof AttackMove && !move.hasAttr(FixedDamageAttr)) {
           this.scene.applyModifiers(PokemonMultiHitModifier, user.isPlayer(), user, hitCount, new Utils.IntegerHolder(0));
@@ -2951,11 +2955,11 @@ export class MoveEffectPhase extends PokemonPhase {
       const moveHistoryEntry = { move: this.move.moveId, targets: this.targets, result: MoveResult.PENDING, virtual: this.move.virtual };
 
       const targetHitChecks = Object.fromEntries(targets.map(p => [p.getBattlerIndex(), this.hitCheck(p)]));
-      const activeTargets = targets.map(t => t.isActive(true));
-      if (!activeTargets.length || (!move.hasAttr(VariableTargetAttr) && !move.isMultiTarget() && !targetHitChecks[this.targets[0]])) {
+      const hasActiveTargets = targets.some(t => t.isActive(true));
+      if (!hasActiveTargets || (!move.hasAttr(VariableTargetAttr) && !move.isMultiTarget() && !targetHitChecks[this.targets[0]])) {
         this.stopMultiHit();
-        if (activeTargets.length) {
-          this.scene.queueMessage(i18next.t("battle:attackMissed", { pokemonNameWithAffix: getPokemonNameWithAffix(this.getTarget()) }));
+        if (hasActiveTargets) {
+          this.scene.queueMessage(i18next.t("battle:attackMissed", { pokemonNameWithAffix: this.getTarget()? getPokemonNameWithAffix(this.getTarget()!) : "" }));
           moveHistoryEntry.result = MoveResult.MISS;
           applyMoveAttrs(MissEffectAttr, user, null, move);
         } else {
@@ -2969,7 +2973,7 @@ export class MoveEffectPhase extends PokemonPhase {
       const applyAttrs: Promise<void>[] = [];
 
       // Move animation only needs one target
-      new MoveAnim(move.id as Moves, user, this.getTarget()?.getBattlerIndex()).play(this.scene, () => {
+      new MoveAnim(move.id as Moves, user, this.getTarget()?.getBattlerIndex()!).play(this.scene, () => { // TODO: is the bang correct here?
         /** Has the move successfully hit a target (for damage) yet? */
         let hasHit: boolean = false;
         for (const target of targets) {
@@ -3018,7 +3022,7 @@ export class MoveEffectPhase extends PokemonPhase {
             applyFilteredMoveAttrs((attr: MoveAttr) => attr instanceof MoveEffectAttr && attr.trigger === MoveEffectTrigger.PRE_APPLY && (!attr.firstHitOnly || firstHit) && (!attr.lastHitOnly || lastHit) && hitResult !== HitResult.NO_EFFECT,
               user, target, move).then(() => {
               if (hitResult !== HitResult.FAIL) {
-                const chargeEffect = !!move.getAttrs(ChargeAttr).find(ca => ca.usedChargeEffect(user, this.getTarget(), move));
+                const chargeEffect = !!move.getAttrs(ChargeAttr).find(ca => ca.usedChargeEffect(user, this.getTarget() ?? null, move));
                 // Charge attribute with charge effect takes all effect attributes and applies them to charge stage, so ignore them if this is present
                 Utils.executeIf(!chargeEffect, () => applyFilteredMoveAttrs((attr: MoveAttr) => attr instanceof MoveEffectAttr && attr.trigger === MoveEffectTrigger.POST_APPLY
                     && attr.selfTarget && (!attr.firstHitOnly || firstHit) && (!attr.lastHitOnly || lastHit), user, target, move)).then(() => {
@@ -3082,13 +3086,13 @@ export class MoveEffectPhase extends PokemonPhase {
     move.type = move.defaultType;
     const user = this.getUserPokemon();
     if (user) {
-      if (--user.turnData.hitsLeft >= 1 && this.getTarget()?.isActive()) {
+      if (user.turnData.hitsLeft && --user.turnData.hitsLeft >= 1 && this.getTarget()?.isActive()) {
         this.scene.unshiftPhase(this.getNewHitPhase());
       } else {
         // Queue message for number of hits made by multi-move
         // If multi-hit attack only hits once, still want to render a message
-        const hitsTotal = user.turnData.hitCount - Math.max(user.turnData.hitsLeft, 0);
-        if (hitsTotal > 1 || user.turnData.hitsLeft > 0) {
+        const hitsTotal = user.turnData.hitCount! - Math.max(user.turnData.hitsLeft!, 0); // TODO: are those bangs correct?
+        if (hitsTotal > 1 || (user.turnData.hitsLeft && user.turnData.hitsLeft > 0)) {
           // If there are multiple hits, or if there are hits of the multi-hit move left
           this.scene.queueMessage(i18next.t("battle:attackHitsCount", { count: hitsTotal }));
         }
@@ -3105,7 +3109,7 @@ export class MoveEffectPhase extends PokemonPhase {
       return true;
     }
 
-    const user = this.getUserPokemon();
+    const user = this.getUserPokemon()!; // TODO: is this bang correct?
 
     // Hit check only calculated on first hit for multi-hit moves unless flag is set to check all hits.
     // However, if an ability with the MaxMultiHitAbAttr, namely Skill Link, is present, act as a normal
@@ -3134,7 +3138,7 @@ export class MoveEffectPhase extends PokemonPhase {
       return false;
     }
 
-    const moveAccuracy = this.move.getMove().calculateBattleAccuracy(user, target);
+    const moveAccuracy = this.move.getMove().calculateBattleAccuracy(user!, target); // TODO: is the bang correct here?
 
     if (moveAccuracy === -1) {
       return true;
@@ -3143,12 +3147,12 @@ export class MoveEffectPhase extends PokemonPhase {
     const accuracyMultiplier = user.getAccuracyMultiplier(target, this.move.getMove());
     const rand = user.randSeedInt(100, 1);
 
-    return rand <= moveAccuracy * accuracyMultiplier;
+    return rand <= moveAccuracy * (accuracyMultiplier!); // TODO: is this bang correct?
   }
 
-  getUserPokemon(): Pokemon {
+  getUserPokemon(): Pokemon | undefined {
     if (this.battlerIndex > BattlerIndex.ENEMY_2) {
-      return this.scene.getPokemonById(this.battlerIndex);
+      return this.scene.getPokemonById(this.battlerIndex) ?? undefined;
     }
     return (this.player ? this.scene.getPlayerField() : this.scene.getEnemyField())[this.fieldIndex];
   }
@@ -3157,7 +3161,7 @@ export class MoveEffectPhase extends PokemonPhase {
     return this.scene.getField(true).filter(p => this.targets.indexOf(p.getBattlerIndex()) > -1);
   }
 
-  getTarget(): Pokemon {
+  getTarget(): Pokemon | undefined {
     return this.getTargets().find(() => true);
   }
 
@@ -3178,8 +3182,8 @@ export class MoveEffectPhase extends PokemonPhase {
      * targets, completely cancel all subsequent strikes.
     */
     if (!target || this.targets.length === 0 ) {
-      this.getUserPokemon().turnData.hitCount = 1;
-      this.getUserPokemon().turnData.hitsLeft = 1;
+      this.getUserPokemon()!.turnData.hitCount = 1; // TODO: is the bang correct here?
+      this.getUserPokemon()!.turnData.hitsLeft = 1; // TODO: is the bang correct here?
     }
   }
 
@@ -3233,7 +3237,7 @@ export class MoveAnimTestPhase extends BattlePhase {
     initMoveAnim(this.scene, moveId).then(() => {
       loadMoveAnimAssets(this.scene, [moveId], true)
         .then(() => {
-          new MoveAnim(moveId, player ? this.scene.getPlayerPokemon() : this.scene.getEnemyPokemon(), (player !== (allMoves[moveId] instanceof SelfStatusMove) ? this.scene.getEnemyPokemon() : this.scene.getPlayerPokemon()).getBattlerIndex()).play(this.scene, () => {
+          new MoveAnim(moveId, player ? this.scene.getPlayerPokemon()! : this.scene.getEnemyPokemon()!, (player !== (allMoves[moveId] instanceof SelfStatusMove) ? this.scene.getEnemyPokemon()! : this.scene.getPlayerPokemon()!).getBattlerIndex()).play(this.scene, () => { // TODO: are the bangs correct here?
             if (player) {
               this.playMoveAnim(moveQueue, false);
             } else {
@@ -3259,16 +3263,19 @@ export class ShowAbilityPhase extends PokemonPhase {
 
     const pokemon = this.getPokemon();
 
-    this.scene.abilityBar.showAbility(pokemon, this.passive);
-    if (pokemon.battleData) {
-      pokemon.battleData.abilityRevealed = true;
+    if (pokemon) {
+      this.scene.abilityBar.showAbility(pokemon, this.passive);
+
+      if (pokemon?.battleData) {
+        pokemon.battleData.abilityRevealed = true;
+      }
     }
 
     this.end();
   }
 }
 
-export type StatChangeCallback = (target: Pokemon, changed: BattleStat[], relativeChanges: number[]) => void;
+export type StatChangeCallback = (target: Pokemon | null, changed: BattleStat[], relativeChanges: number[]) => void;
 
 export class StatChangePhase extends PokemonPhase {
   private stats: BattleStat[];
@@ -3277,10 +3284,10 @@ export class StatChangePhase extends PokemonPhase {
   private showMessage: boolean;
   private ignoreAbilities: boolean;
   private canBeCopied: boolean;
-  private onChange: StatChangeCallback;
+  private onChange: StatChangeCallback | null;
 
 
-  constructor(scene: BattleScene, battlerIndex: BattlerIndex, selfTarget: boolean, stats: BattleStat[], levels: integer, showMessage: boolean = true, ignoreAbilities: boolean = false, canBeCopied: boolean = true, onChange: StatChangeCallback = null) {
+  constructor(scene: BattleScene, battlerIndex: BattlerIndex, selfTarget: boolean, stats: BattleStat[], levels: integer, showMessage: boolean = true, ignoreAbilities: boolean = false, canBeCopied: boolean = true, onChange: StatChangeCallback | null = null) {
     super(scene, battlerIndex);
 
     this.selfTarget = selfTarget;
@@ -3329,9 +3336,9 @@ export class StatChangePhase extends PokemonPhase {
     }
 
     const battleStats = this.getPokemon().summonData.battleStats;
-    const relLevels = filteredStats.map(stat => (levels.value >= 1 ? Math.min(battleStats[stat] + levels.value, 6) : Math.max(battleStats[stat] + levels.value, -6)) - battleStats[stat]);
+    const relLevels = filteredStats.map(stat => (levels.value >= 1 ? Math.min(battleStats![stat] + levels.value, 6) : Math.max(battleStats![stat] + levels.value, -6)) - battleStats![stat]);
 
-    this.onChange?.(this.getPokemon(), filteredStats, relLevels);
+    this.onChange && this.onChange(this.getPokemon(), filteredStats, relLevels);
 
     const end = () => {
       if (this.showMessage) {
@@ -3393,7 +3400,7 @@ export class StatChangePhase extends PokemonPhase {
 
       this.scene.playSound(`stat_${levels.value >= 1 ? "up" : "down"}`);
 
-      statSprite.setMask(new Phaser.Display.Masks.BitmapMask(this.scene, pokemonMaskSprite));
+      statSprite.setMask(new Phaser.Display.Masks.BitmapMask(this.scene, pokemonMaskSprite ?? undefined));
 
       this.scene.tweens.add({
         targets: statSprite,
@@ -3426,7 +3433,7 @@ export class StatChangePhase extends PokemonPhase {
 
   getRandomStat(): BattleStat {
     const allStats = Utils.getEnumValues(BattleStat);
-    return allStats[this.getPokemon().randSeedInt(BattleStat.SPD + 1)];
+    return this.getPokemon() ? allStats[this.getPokemon()!.randSeedInt(BattleStat.SPD + 1)] : BattleStat.ATK; // TODO: return default ATK on random? idk...
   }
 
   aggregateStatChanges(random: boolean = false): void {
@@ -3491,7 +3498,7 @@ export class StatChangePhase extends PokemonPhase {
 }
 
 export class WeatherEffectPhase extends CommonAnimPhase {
-  public weather: Weather;
+  public weather: Weather | null;
 
   constructor(scene: BattleScene) {
     super(scene, undefined, undefined, CommonAnim.SUNNY + ((scene?.arena?.weather?.weatherType || WeatherType.NONE) - 1));
@@ -3519,7 +3526,7 @@ export class WeatherEffectPhase extends CommonAnimPhase {
         const inflictDamage = (pokemon: Pokemon) => {
           const cancelled = new Utils.BooleanHolder(false);
 
-          applyPreWeatherEffectAbAttrs(PreWeatherDamageAbAttr, pokemon, this.weather, cancelled);
+          applyPreWeatherEffectAbAttrs(PreWeatherDamageAbAttr, pokemon, this.weather , cancelled);
           applyAbAttrs(BlockNonDirectDamageAbAttr, pokemon, cancelled);
 
           if (cancelled.value) {
@@ -3528,12 +3535,12 @@ export class WeatherEffectPhase extends CommonAnimPhase {
 
           const damage = Math.ceil(pokemon.getMaxHp() / 16);
 
-          this.scene.queueMessage(getWeatherDamageMessage(this.weather.weatherType, pokemon));
+          this.scene.queueMessage(getWeatherDamageMessage(this.weather?.weatherType!, pokemon)!); // TODO: are those bangs correct?
           pokemon.damageAndUpdate(damage, HitResult.EFFECTIVE, false, false, true);
         };
 
         this.executeForAll((pokemon: Pokemon) => {
-          const immune = !pokemon || !!pokemon.getTypes(true, true).filter(t => this.weather.isTypeDamageImmune(t)).length;
+          const immune = !pokemon || !!pokemon.getTypes(true, true).filter(t => this.weather?.isTypeDamageImmune(t)).length;
           if (!immune) {
             inflictDamage(pokemon);
           }
@@ -3541,7 +3548,7 @@ export class WeatherEffectPhase extends CommonAnimPhase {
       }
     }
 
-    this.scene.ui.showText(getWeatherLapseMessage(this.weather.weatherType), null, () => {
+    this.scene.ui.showText(getWeatherLapseMessage(this.weather.weatherType)!, null, () => { // TODO: is this bang correct?
       this.executeForAll((pokemon: Pokemon) => applyPostWeatherLapseAbAttrs(PostWeatherLapseAbAttr, pokemon, this.weather));
 
       super.start();
@@ -3550,31 +3557,31 @@ export class WeatherEffectPhase extends CommonAnimPhase {
 }
 
 export class ObtainStatusEffectPhase extends PokemonPhase {
-  private statusEffect: StatusEffect;
-  private cureTurn: integer;
-  private sourceText: string;
-  private sourcePokemon: Pokemon;
+  private statusEffect: StatusEffect | undefined;
+  private cureTurn: integer | null;
+  private sourceText: string | null;
+  private sourcePokemon: Pokemon | null;
 
-  constructor(scene: BattleScene, battlerIndex: BattlerIndex, statusEffect: StatusEffect, cureTurn?: integer, sourceText?: string, sourcePokemon?: Pokemon) {
+  constructor(scene: BattleScene, battlerIndex: BattlerIndex, statusEffect?: StatusEffect, cureTurn?: integer | null, sourceText?: string, sourcePokemon?: Pokemon) {
     super(scene, battlerIndex);
 
     this.statusEffect = statusEffect;
-    this.cureTurn = cureTurn;
-    this.sourceText = sourceText;
-    this.sourcePokemon = sourcePokemon; // For tracking which Pokemon caused the status effect
+    this.cureTurn = cureTurn!; // TODO: is this bang correct?
+    this.sourceText = sourceText!; // TODO: is this bang correct?
+    this.sourcePokemon = sourcePokemon!; // For tracking which Pokemon caused the status effect // TODO: is this bang correct?
   }
 
   start() {
     const pokemon = this.getPokemon();
-    if (!pokemon.status) {
-      if (pokemon.trySetStatus(this.statusEffect, false, this.sourcePokemon)) {
+    if (!pokemon?.status) {
+      if (pokemon?.trySetStatus(this.statusEffect, false, this.sourcePokemon)) {
         if (this.cureTurn) {
-          pokemon.status.cureTurn = this.cureTurn;
+          pokemon.status!.cureTurn = this.cureTurn; // TODO: is this bang correct?
         }
         pokemon.updateInfo(true);
-        new CommonBattleAnim(CommonAnim.POISON + (this.statusEffect - 1), pokemon).play(this.scene, () => {
-          this.scene.queueMessage(getStatusEffectObtainText(this.statusEffect, getPokemonNameWithAffix(pokemon), this.sourceText));
-          if (pokemon.status.isPostTurn()) {
+        new CommonBattleAnim(CommonAnim.POISON + (this.statusEffect! - 1), pokemon).play(this.scene, () => {
+          this.scene.queueMessage(getStatusEffectObtainText(this.statusEffect, getPokemonNameWithAffix(pokemon), this.sourceText ?? undefined));
+          if (pokemon.status?.isPostTurn()) {
             this.scene.pushPhase(new PostTurnStatusEffectPhase(this.scene, this.battlerIndex));
           }
           this.end();
@@ -3640,17 +3647,17 @@ export class PostTurnStatusEffectPhase extends PokemonPhase {
 
 export class MessagePhase extends Phase {
   private text: string;
-  private callbackDelay: integer;
-  private prompt: boolean;
-  private promptDelay: integer;
+  private callbackDelay: integer | null;
+  private prompt: boolean | null;
+  private promptDelay: integer | null;
 
-  constructor(scene: BattleScene, text: string, callbackDelay?: integer, prompt?: boolean, promptDelay?: integer) {
+  constructor(scene: BattleScene, text: string, callbackDelay?: integer | null, prompt?: boolean | null, promptDelay?: integer | null) {
     super(scene);
 
     this.text = text;
-    this.callbackDelay = callbackDelay;
-    this.prompt = prompt;
-    this.promptDelay = promptDelay;
+    this.callbackDelay = callbackDelay!; // TODO: is this bang correct?
+    this.prompt = prompt!; // TODO: is this bang correct?
+    this.promptDelay = promptDelay!; // TODO: is this bang correct?
   }
 
   start() {
@@ -3758,7 +3765,7 @@ export class FaintPhase extends PokemonPhase {
   constructor(scene: BattleScene, battlerIndex: BattlerIndex, preventEndure?: boolean) {
     super(scene, battlerIndex);
 
-    this.preventEndure = preventEndure;
+    this.preventEndure = preventEndure!; // TODO: is this bang correct?
   }
 
   start() {
@@ -3795,7 +3802,7 @@ export class FaintPhase extends PokemonPhase {
 
     if (pokemon.turnData?.attacksReceived?.length) {
       const lastAttack = pokemon.turnData.attacksReceived[0];
-      applyPostFaintAbAttrs(PostFaintAbAttr, pokemon, this.scene.getPokemonById(lastAttack.sourceId), new PokemonMove(lastAttack.move).getMove(), lastAttack.result);
+      applyPostFaintAbAttrs(PostFaintAbAttr, pokemon, this.scene.getPokemonById(lastAttack.sourceId)!, new PokemonMove(lastAttack.move).getMove(), lastAttack.result); // TODO: is this bang correct?
     }
 
     const alivePlayField = this.scene.getField(true);
@@ -3916,7 +3923,7 @@ export class VictoryPhase extends PokemonPhase {
     const multipleParticipantExpBonusModifier = this.scene.findModifier(m => m instanceof MultipleParticipantExpBonusModifier) as MultipleParticipantExpBonusModifier;
     const nonFaintedPartyMembers = party.filter(p => p.hp);
     const expPartyMembers = nonFaintedPartyMembers.filter(p => p.level < this.scene.getMaxExpLevel());
-    const partyMemberExp = [];
+    const partyMemberExp: number[] = [];
 
     if (participantIds.size) {
       let expValue = this.getPokemon().getExpValue();
@@ -3968,7 +3975,7 @@ export class VictoryPhase extends PokemonPhase {
 
         const medianLevel = Math.floor(totalLevel / expPartyMembers.length);
 
-        const recipientExpPartyMemberIndexes = [];
+        const recipientExpPartyMemberIndexes: number[] = [];
         expPartyMembers.forEach((expPartyMember, epm) => {
           if (expPartyMember.level <= medianLevel) {
             recipientExpPartyMemberIndexes.push(epm);
@@ -4043,39 +4050,40 @@ export class TrainerVictoryPhase extends BattlePhase {
   start() {
     this.scene.disableMenu = true;
 
-    this.scene.playBgm(this.scene.currentBattle.trainer.config.victoryBgm);
+    this.scene.playBgm(this.scene.currentBattle.trainer?.config.victoryBgm);
 
-    this.scene.unshiftPhase(new MoneyRewardPhase(this.scene, this.scene.currentBattle.trainer.config.moneyMultiplier));
+    this.scene.unshiftPhase(new MoneyRewardPhase(this.scene, this.scene.currentBattle.trainer?.config.moneyMultiplier!)); // TODO: is this bang correct?
 
-    const modifierRewardFuncs = this.scene.currentBattle.trainer.config.modifierRewardFuncs;
+    const modifierRewardFuncs = this.scene.currentBattle.trainer?.config.modifierRewardFuncs!; // TODO: is this bang correct?
     for (const modifierRewardFunc of modifierRewardFuncs) {
       this.scene.unshiftPhase(new ModifierRewardPhase(this.scene, modifierRewardFunc));
     }
 
-    const trainerType = this.scene.currentBattle.trainer.config.trainerType;
+    const trainerType = this.scene.currentBattle.trainer?.config.trainerType!; // TODO: is this bang correct?
     if (vouchers.hasOwnProperty(TrainerType[trainerType])) {
-      if (!this.scene.validateVoucher(vouchers[TrainerType[trainerType]]) && this.scene.currentBattle.trainer.config.isBoss) {
+      if (!this.scene.validateVoucher(vouchers[TrainerType[trainerType]]) && this.scene.currentBattle.trainer?.config.isBoss) {
         this.scene.unshiftPhase(new ModifierRewardPhase(this.scene, [modifierTypes.VOUCHER, modifierTypes.VOUCHER, modifierTypes.VOUCHER_PLUS, modifierTypes.VOUCHER_PREMIUM][vouchers[TrainerType[trainerType]].voucherType]));
       }
     }
 
-    this.scene.ui.showText(i18next.t("battle:trainerDefeated", { trainerName: this.scene.currentBattle.trainer.getName(TrainerSlot.NONE, true) }), null, () => {
-      const victoryMessages = this.scene.currentBattle.trainer.getVictoryMessages();
+    this.scene.ui.showText(i18next.t("battle:trainerDefeated", { trainerName: this.scene.currentBattle.trainer?.getName(TrainerSlot.NONE, true) }), null, () => {
+      const victoryMessages = this.scene.currentBattle.trainer?.getVictoryMessages()!; // TODO: is this bang correct?
       let message: string;
       this.scene.executeWithSeedOffset(() => message = Utils.randSeedItem(victoryMessages), this.scene.currentBattle.waveIndex);
+      message = message!; // tell TS compiler it's defined now
 
       const showMessage = () => {
         const originalFunc = showMessageOrEnd;
-        showMessageOrEnd = () => this.scene.ui.showDialogue(message, this.scene.currentBattle.trainer.getName(), null, originalFunc);
+        showMessageOrEnd = () => this.scene.ui.showDialogue(message, this.scene.currentBattle.trainer?.getName(), null, originalFunc);
 
         showMessageOrEnd();
       };
       let showMessageOrEnd = () => this.end();
       if (victoryMessages?.length) {
-        if (this.scene.currentBattle.trainer.config.hasCharSprite && !this.scene.ui.shouldSkipDialogue(message)) {
+        if (this.scene.currentBattle.trainer?.config.hasCharSprite && !this.scene.ui.shouldSkipDialogue(message)) {
           const originalFunc = showMessageOrEnd;
           showMessageOrEnd = () => this.scene.charSprite.hide().then(() => this.scene.hideFieldOverlay(250).then(() => originalFunc()));
-          this.scene.showFieldOverlay(500).then(() => this.scene.charSprite.showCharacter(this.scene.currentBattle.trainer.getKey(), getCharVariantFromDialogue(victoryMessages[0])).then(() => showMessage()));
+          this.scene.showFieldOverlay(500).then(() => this.scene.charSprite.showCharacter(this.scene.currentBattle.trainer?.getKey()!, getCharVariantFromDialogue(victoryMessages[0])).then(() => showMessage())); // TODO: is this bang correct?
         } else {
           showMessage();
         }
@@ -4136,7 +4144,7 @@ export class ModifierRewardPhase extends BattlePhase {
       const newModifier = this.modifierType.newModifier();
       this.scene.addModifier(newModifier).then(() => {
         this.scene.playSound("item_fanfare");
-        this.scene.ui.showText(i18next.t("battle:rewardGain", { modifierName: newModifier.type.name }), null, () => resolve(), null, true);
+        this.scene.ui.showText(i18next.t("battle:rewardGain", { modifierName: newModifier?.type.name }), null, () => resolve(), null, true);
       });
     });
   }
@@ -4154,7 +4162,7 @@ export class GameOverModifierRewardPhase extends ModifierRewardPhase {
         this.scene.playSound("level_up_fanfare");
         this.scene.ui.setMode(Mode.MESSAGE);
         this.scene.ui.fadeIn(250).then(() => {
-          this.scene.ui.showText(i18next.t("battle:rewardGain", { modifierName: newModifier.type.name }), null, () => {
+          this.scene.ui.showText(i18next.t("battle:rewardGain", { modifierName: newModifier?.type.name }), null, () => {
             this.scene.time.delayedCall(1500, () => this.scene.arenaBg.setVisible(true));
             resolve();
           }, null, true, 1500);
@@ -4182,7 +4190,7 @@ export class RibbonModifierRewardPhase extends ModifierRewardPhase {
         this.scene.ui.showText(i18next.t("battle:beatModeFirstTime", {
           speciesName: this.species.name,
           gameMode: this.scene.gameMode.getName(),
-          newModifier: newModifier.type.name
+          newModifier: newModifier?.type.name
         }), null, () => {
           resolve();
         }, null, true, 1500);
@@ -4423,12 +4431,12 @@ export class UnlockPhase extends Phase {
 }
 
 export class PostGameOverPhase extends Phase {
-  private endCardPhase: EndCardPhase;
+  private endCardPhase: EndCardPhase | null;
 
-  constructor(scene: BattleScene, endCardPhase: EndCardPhase) {
+  constructor(scene: BattleScene, endCardPhase?: EndCardPhase) {
     super(scene);
 
-    this.endCardPhase = endCardPhase;
+    this.endCardPhase = endCardPhase!; // TODO: is this bang correct?
   }
 
   start() {
@@ -4454,8 +4462,8 @@ export class PostGameOverPhase extends Phase {
       this.scene.ui.fadeOut(500).then(() => {
         this.scene.ui.getMessageHandler().bg.setVisible(true);
 
-        this.endCardPhase.endCard.destroy();
-        this.endCardPhase.text.destroy();
+        this.endCardPhase?.endCard.destroy();
+        this.endCardPhase?.text.destroy();
         saveAndReset();
       });
     } else {
@@ -4734,7 +4742,7 @@ export class LearnMovePhase extends PlayerPartyMemberPokemonPhase {
                     }
                     this.scene.ui.setMode(messageMode).then(() => {
                       this.scene.ui.showText(i18next.t("battle:countdownPoof"), null, () => {
-                        this.scene.ui.showText(i18next.t("battle:learnMoveForgetSuccess", { pokemonName: getPokemonNameWithAffix(pokemon), moveName: pokemon.moveset[moveIndex].getName() }), null, () => {
+                        this.scene.ui.showText(i18next.t("battle:learnMoveForgetSuccess", { pokemonName: getPokemonNameWithAffix(pokemon), moveName: pokemon.moveset[moveIndex]!.getName() }), null, () => { // TODO: is the bang correct?
                           this.scene.ui.showText(i18next.t("battle:learnMoveAnd"), null, () => {
                             pokemon.setMove(moveIndex, Moves.NONE);
                             this.scene.unshiftPhase(new LearnMovePhase(this.scene, this.partyMemberIndex, this.moveId));
@@ -4756,14 +4764,14 @@ export class LearnMovePhase extends PlayerPartyMemberPokemonPhase {
 
 export class PokemonHealPhase extends CommonAnimPhase {
   private hpHealed: integer;
-  private message: string;
+  private message: string | null;
   private showFullHpMessage: boolean;
   private skipAnim: boolean;
   private revive: boolean;
   private healStatus: boolean;
   private preventFullHeal: boolean;
 
-  constructor(scene: BattleScene, battlerIndex: BattlerIndex, hpHealed: integer, message: string, showFullHpMessage: boolean, skipAnim: boolean = false, revive: boolean = false, healStatus: boolean = false, preventFullHeal: boolean = false) {
+  constructor(scene: BattleScene, battlerIndex: BattlerIndex, hpHealed: integer, message: string | null, showFullHpMessage: boolean, skipAnim: boolean = false, revive: boolean = false, healStatus: boolean = false, preventFullHeal: boolean = false) {
     super(scene, battlerIndex, undefined, CommonAnim.HEALTH_UP);
 
     this.hpHealed = hpHealed;
@@ -5171,7 +5179,7 @@ export class SelectModifierPhase extends BattlePhase {
     super(scene);
 
     this.rerollCount = rerollCount;
-    this.modifierTiers = modifierTiers;
+    this.modifierTiers = modifierTiers!; // TODO: is this bang correct?
   }
 
   start() {
@@ -5214,7 +5222,7 @@ export class SelectModifierPhase extends BattlePhase {
             return false;
           } else {
             this.scene.reroll = true;
-            this.scene.unshiftPhase(new SelectModifierPhase(this.scene, this.rerollCount + 1, typeOptions.map(o => o.type.tier)));
+            this.scene.unshiftPhase(new SelectModifierPhase(this.scene, this.rerollCount + 1, typeOptions.map(o => o.type?.tier).filter(t => t !== undefined) as ModifierTier[]));
             this.scene.ui.clearText();
             this.scene.ui.setMode(Mode.MESSAGE).then(() => super.end());
             if (!Overrides.WAIVE_ROLL_FEE_OVERRIDE) {
@@ -5252,17 +5260,21 @@ export class SelectModifierPhase extends BattlePhase {
         }
         return true;
       case 1:
-        modifierType = typeOptions[cursor].type;
+        if (typeOptions[cursor].type) {
+          modifierType = typeOptions[cursor].type;
+        }
         break;
       default:
         const shopOptions = getPlayerShopModifierTypeOptionsForWave(this.scene.currentBattle.waveIndex, this.scene.getWaveMoneyAmount(1));
         const shopOption = shopOptions[rowCursor > 2 || shopOptions.length <= SHOP_OPTIONS_ROW_LIMIT ? cursor : cursor + SHOP_OPTIONS_ROW_LIMIT];
-        modifierType = shopOption.type;
+        if (shopOption.type) {
+          modifierType = shopOption.type;
+        }
         cost = shopOption.cost;
         break;
       }
 
-      if (cost && (this.scene.money < cost) && !Overrides.WAIVE_ROLL_FEE_OVERRIDE) {
+      if (cost! && (this.scene.money < cost) && !Overrides.WAIVE_ROLL_FEE_OVERRIDE) { // TODO: is the bang on cost correct?
         this.scene.ui.playError();
         return false;
       }
@@ -5297,12 +5309,12 @@ export class SelectModifierPhase extends BattlePhase {
         }
       };
 
-      if (modifierType instanceof PokemonModifierType) {
+      if (modifierType! instanceof PokemonModifierType) { //TODO: is the bang correct?
         if (modifierType instanceof FusePokemonModifierType) {
           this.scene.ui.setModeWithoutClear(Mode.PARTY, PartyUiMode.SPLICE, -1, (fromSlotIndex: integer, spliceSlotIndex: integer) => {
             if (spliceSlotIndex !== undefined && fromSlotIndex < 6 && spliceSlotIndex < 6 && fromSlotIndex !== spliceSlotIndex) {
               this.scene.ui.setMode(Mode.MODIFIER_SELECT, this.isPlayer()).then(() => {
-                const modifier = modifierType.newModifier(party[fromSlotIndex], party[spliceSlotIndex]);
+                const modifier = modifierType.newModifier(party[fromSlotIndex], party[spliceSlotIndex])!; //TODO: is the bang correct?
                 applyModifier(modifier, true);
               });
             } else {
@@ -5330,7 +5342,7 @@ export class SelectModifierPhase extends BattlePhase {
                     ? modifierType.newModifier(party[slotIndex])
                     : modifierType.newModifier(party[slotIndex], option as integer)
                   : modifierType.newModifier(party[slotIndex], option - PartyOption.MOVE_1);
-                applyModifier(modifier, true);
+                applyModifier(modifier!, true); // TODO: is the bang correct?
               });
             } else {
               this.scene.ui.setMode(Mode.MODIFIER_SELECT, this.isPlayer(), typeOptions, modifierSelectCallback, this.getRerollCost(typeOptions, this.scene.lockModifierTiers));
@@ -5338,10 +5350,10 @@ export class SelectModifierPhase extends BattlePhase {
           }, pokemonModifierType.selectFilter, modifierType instanceof PokemonMoveModifierType ? (modifierType as PokemonMoveModifierType).moveSelectFilter : undefined, tmMoveId, isPpRestoreModifier);
         }
       } else {
-        applyModifier(modifierType.newModifier());
+        applyModifier(modifierType!.newModifier()!); // TODO: is the bang correct?
       }
 
-      return !cost;
+      return !cost!;// TODO: is the bang correct?
     };
     this.scene.ui.setMode(Mode.MODIFIER_SELECT, this.isPlayer(), typeOptions, modifierSelectCallback, this.getRerollCost(typeOptions, this.scene.lockModifierTiers));
   }
@@ -5361,7 +5373,7 @@ export class SelectModifierPhase extends BattlePhase {
     } else if (lockRarities) {
       const tierValues = [50, 125, 300, 750, 2000];
       for (const opt of typeOptions) {
-        baseValue += tierValues[opt.type.tier];
+        baseValue += opt.type?.tier ? tierValues[opt.type.tier] : 0;
       }
     } else {
       baseValue = 250;
@@ -5496,7 +5508,7 @@ export class PartyHealPhase extends BattlePhase {
         pokemon.hp = pokemon.getMaxHp();
         pokemon.resetStatus();
         for (const move of pokemon.moveset) {
-          move.ppUsed = 0;
+          move!.ppUsed = 0; // TODO: is this bang correct?
         }
         pokemon.updateInfo(true);
       }
diff --git a/src/pipelines/sprite.ts b/src/pipelines/sprite.ts
index 741c31183d4..c9a76dc50a4 100644
--- a/src/pipelines/sprite.ts
+++ b/src/pipelines/sprite.ts
@@ -377,7 +377,7 @@ export default class SpritePipeline extends FieldSpritePipeline {
     this.set2f("texSize", sprite.texture.source[0].width, sprite.texture.source[0].height);
     this.set1f("yOffset", sprite.height - sprite.frame.height * (isEntityObj ? sprite.parentContainer.scale : sprite.scale));
     this.set4fv("tone", tone);
-    this.bindTexture(this.game.textures.get("tera").source[0].glTexture, 1);
+    this.bindTexture(this.game.textures.get("tera").source[0].glTexture!, 1); // TODO: is this bang correct?
 
     if ((gameObject.scene as BattleScene).fusionPaletteSwaps) {
       const spriteColors = ((ignoreOverride && data["spriteColorsBase"]) || data["spriteColors"] || []) as number[][];
diff --git a/src/plugins/i18n.ts b/src/plugins/i18n.ts
index 54dc545868c..82cde7cd2ad 100644
--- a/src/plugins/i18n.ts
+++ b/src/plugins/i18n.ts
@@ -157,7 +157,7 @@ export async function initI18n(): Promise<void> {
     postProcess: ["korean-postposition"],
   });
 
-  await initFonts(localStorage.getItem("prLang"));
+  await initFonts(localStorage.getItem("prLang") ?? undefined);
 }
 
 export default i18next;
diff --git a/src/system/achv.ts b/src/system/achv.ts
index 0dcf74ce3a5..b1f575fb31c 100644
--- a/src/system/achv.ts
+++ b/src/system/achv.ts
@@ -6,6 +6,7 @@ import * as Utils from "../utils";
 import { PlayerGender } from "#enums/player-gender";
 import { ParseKeys } from "i18next";
 import { Challenge, FreshStartChallenge, SingleGenerationChallenge, SingleTypeChallenge } from "#app/data/challenge.js";
+import { ConditionFn } from "#app/@types/common.js";
 
 export enum AchvTier {
   COMMON,
@@ -27,9 +28,9 @@ export class Achv {
   public hasParent: boolean;
   public parentId: string;
 
-  private conditionFunc: (scene: BattleScene, args: any[]) => boolean;
+  private conditionFunc: ConditionFn | undefined;
 
-  constructor(localizationKey:string, name: string, description: string, iconImage: string, score: integer, conditionFunc?: (scene: BattleScene, args: any[]) => boolean) {
+  constructor(localizationKey:string, name: string, description: string, iconImage: string, score: integer, conditionFunc?: ConditionFn) {
     this.name = name;
     this.description = description;
     this.iconImage = iconImage;
@@ -63,7 +64,7 @@ export class Achv {
     return this;
   }
 
-  validate(scene: BattleScene, args: any[]): boolean {
+  validate(scene: BattleScene, args?: any[]): boolean {
     return !this.conditionFunc || this.conditionFunc(scene, args);
   }
 
diff --git a/src/system/arena-data.ts b/src/system/arena-data.ts
index f6db53d7f7f..886129edcf6 100644
--- a/src/system/arena-data.ts
+++ b/src/system/arena-data.ts
@@ -6,15 +6,15 @@ import { Terrain } from "#app/data/terrain.js";
 
 export default class ArenaData {
   public biome: Biome;
-  public weather: Weather;
-  public terrain: Terrain;
+  public weather: Weather | null;
+  public terrain: Terrain | null;
   public tags: ArenaTag[];
 
   constructor(source: Arena | any) {
     const sourceArena = source instanceof Arena ? source as Arena : null;
     this.biome = sourceArena ? sourceArena.biomeType : source.biome;
-    this.weather = sourceArena ? sourceArena.weather : source.weather ? new Weather(source.weather.weatherType, source.weather.turnsLeft) : undefined;
-    this.terrain = sourceArena ? sourceArena.terrain : source.terrain ? new Terrain(source.terrain.terrainType, source.terrain.turnsLeft) : undefined;
+    this.weather = sourceArena ? sourceArena.weather : source.weather ? new Weather(source.weather.weatherType, source.weather.turnsLeft) : null;
+    this.terrain = sourceArena ? sourceArena.terrain : source.terrain ? new Terrain(source.terrain.terrainType, source.terrain.turnsLeft) : null;
     this.tags = sourceArena ? sourceArena.tags : [];
   }
 }
diff --git a/src/system/game-data.ts b/src/system/game-data.ts
index 161b5a2c49b..2cc6ab93c61 100644
--- a/src/system/game-data.ts
+++ b/src/system/game-data.ts
@@ -41,6 +41,8 @@ import { Moves } from "#enums/moves";
 import { PlayerGender } from "#enums/player-gender";
 import { Species } from "#enums/species";
 import { applyChallenges, ChallengeType } from "#app/data/challenge.js";
+import { WeatherType } from "#app/enums/weather-type.js";
+import { TerrainType } from "#app/data/terrain.js";
 
 export const defaultStarterSpecies: Species[] = [
   Species.BULBASAUR, Species.CHARMANDER, Species.SQUIRTLE,
@@ -78,7 +80,7 @@ export function getDataTypeKey(dataType: GameDataType, slotId: integer = 0): str
 export function encrypt(data: string, bypassLogin: boolean): string {
   return (bypassLogin
     ? (data: string) => btoa(data)
-    : (data: string) => AES.encrypt(data, saveKey))(data);
+    : (data: string) => AES.encrypt(data, saveKey))(data) as unknown as string; // TODO: is this correct?
 }
 
 export function decrypt(data: string, bypassLogin: boolean): string {
@@ -230,7 +232,7 @@ export class StarterPrefs {
 }
 
 export interface StarterDataEntry {
-  moveset: StarterMoveset | StarterFormMoveData;
+  moveset: StarterMoveset | StarterFormMoveData | null;
   eggMoves: integer;
   candyCount: integer;
   friendship: integer;
@@ -279,7 +281,7 @@ export class GameData {
   public gender: PlayerGender;
 
   public dexData: DexData;
-  private defaultDexData: DexData;
+  private defaultDexData: DexData | null;
 
   public starterData: StarterData;
 
@@ -352,7 +354,7 @@ export class GameData {
       const maxIntAttrValue = 0x80000000;
       const systemData = JSON.stringify(data, (k: any, v: any) => typeof v === "bigint" ? v <= maxIntAttrValue ? Number(v) : v.toString() : v);
 
-      localStorage.setItem(`data_${loggedInUser.username}`, encrypt(systemData, bypassLogin));
+      localStorage.setItem(`data_${loggedInUser?.username}`, encrypt(systemData, bypassLogin));
 
       if (!bypassLogin) {
         Utils.apiPost(`savedata/system/update?clientSessionId=${clientSessionId}`, systemData, undefined, true)
@@ -384,7 +386,7 @@ export class GameData {
     return new Promise<boolean>(resolve => {
       console.log("Client Session:", clientSessionId);
 
-      if (bypassLogin && !localStorage.getItem(`data_${loggedInUser.username}`)) {
+      if (bypassLogin && !localStorage.getItem(`data_${loggedInUser?.username}`)) {
         return resolve(false);
       }
 
@@ -404,11 +406,11 @@ export class GameData {
               return resolve(false);
             }
 
-            const cachedSystem = localStorage.getItem(`data_${loggedInUser.username}`);
-            this.initSystem(response, cachedSystem ? AES.decrypt(cachedSystem, saveKey).toString(enc.Utf8) : null).then(resolve);
+            const cachedSystem = localStorage.getItem(`data_${loggedInUser?.username}`);
+            this.initSystem(response, cachedSystem ? AES.decrypt(cachedSystem, saveKey).toString(enc.Utf8) : undefined).then(resolve);
           });
       } else {
-        this.initSystem(decrypt(localStorage.getItem(`data_${loggedInUser.username}`), bypassLogin)).then(resolve);
+        this.initSystem(decrypt(localStorage.getItem(`data_${loggedInUser?.username}`)!, bypassLogin)).then(resolve); // TODO: is this bang correct?
       }
     });
   }
@@ -431,7 +433,7 @@ export class GameData {
 
         console.debug(systemData);
 
-        localStorage.setItem(`data_${loggedInUser.username}`, encrypt(systemDataStr, bypassLogin));
+        localStorage.setItem(`data_${loggedInUser?.username}`, encrypt(systemDataStr, bypassLogin));
 
         /*const versions = [ this.scene.game.config.gameVersion, data.gameVersion || '0.0.0' ];
 
@@ -606,9 +608,9 @@ export class GameData {
     if (bypassLogin) {
       return;
     }
-    localStorage.removeItem(`data_${loggedInUser.username}`);
+    localStorage.removeItem(`data_${loggedInUser?.username}`);
     for (let s = 0; s < 5; s++) {
-      localStorage.removeItem(`sessionData${s ? s : ""}_${loggedInUser.username}`);
+      localStorage.removeItem(`sessionData${s ? s : ""}_${loggedInUser?.username}`);
     }
   }
 
@@ -621,7 +623,7 @@ export class GameData {
   public saveSetting(setting: string, valueIndex: integer): boolean {
     let settings: object = {};
     if (localStorage.hasOwnProperty("settings")) {
-      settings = JSON.parse(localStorage.getItem("settings"));
+      settings = JSON.parse(localStorage.getItem("settings")!); // TODO: is this bang correct?
     }
 
     setSetting(this.scene, setting, valueIndex);
@@ -644,7 +646,7 @@ export class GameData {
     const key = deviceName.toLowerCase();  // Convert the gamepad name to lowercase to use as a key
     let mappingConfigs: object = {};  // Initialize an empty object to hold the mapping configurations
     if (localStorage.hasOwnProperty("mappingConfigs")) {// Check if 'mappingConfigs' exists in localStorage
-      mappingConfigs = JSON.parse(localStorage.getItem("mappingConfigs"));
+      mappingConfigs = JSON.parse(localStorage.getItem("mappingConfigs")!); // TODO: is this bang correct?
     }  // Parse the existing 'mappingConfigs' from localStorage
     if (!mappingConfigs[key]) {
       mappingConfigs[key] = {};
@@ -669,7 +671,7 @@ export class GameData {
       return false;
     }  // If 'mappingConfigs' does not exist, return false
 
-    const mappingConfigs = JSON.parse(localStorage.getItem("mappingConfigs"));  // Parse the existing 'mappingConfigs' from localStorage
+    const mappingConfigs = JSON.parse(localStorage.getItem("mappingConfigs")!);  // Parse the existing 'mappingConfigs' from localStorage // TODO: is this bang correct?
 
     for (const key of Object.keys(mappingConfigs)) {// Iterate over the keys of the mapping configurations
       this.scene.inputController.injectConfig(key, mappingConfigs[key]);
@@ -684,6 +686,7 @@ export class GameData {
     }  // If 'mappingConfigs' does not exist, return false
     localStorage.removeItem("mappingConfigs");
     this.scene.inputController.resetConfigs();
+    return true; // TODO: is `true` the correct return value?
   }
 
   /**
@@ -703,7 +706,7 @@ export class GameData {
     let settingsControls: object = {};  // Initialize an empty object to hold the gamepad settings
 
     if (localStorage.hasOwnProperty(localStoragePropertyName)) {  // Check if 'settingsControls' exists in localStorage
-      settingsControls = JSON.parse(localStorage.getItem(localStoragePropertyName));  // Parse the existing 'settingsControls' from localStorage
+      settingsControls = JSON.parse(localStorage.getItem(localStoragePropertyName)!);  // Parse the existing 'settingsControls' from localStorage // TODO: is this bang correct?
     }
 
     if (device === Device.GAMEPAD) {
@@ -734,11 +737,13 @@ export class GameData {
       return false;
     }
 
-    const settings = JSON.parse(localStorage.getItem("settings"));
+    const settings = JSON.parse(localStorage.getItem("settings")!); // TODO: is this bang correct?
 
     for (const setting of Object.keys(settings)) {
       setSetting(this.scene, setting, settings[setting]);
     }
+
+    return true; // TODO: is `true` the correct return value?
   }
 
   private loadGamepadSettings(): boolean {
@@ -747,18 +752,20 @@ export class GameData {
     if (!localStorage.hasOwnProperty("settingsGamepad")) {
       return false;
     }
-    const settingsGamepad = JSON.parse(localStorage.getItem("settingsGamepad"));
+    const settingsGamepad = JSON.parse(localStorage.getItem("settingsGamepad")!); // TODO: is this bang correct?
 
     for (const setting of Object.keys(settingsGamepad)) {
       setSettingGamepad(this.scene, setting as SettingGamepad, settingsGamepad[setting]);
     }
+
+    return true; // TODO: is `true` the correct return value?
   }
 
   public saveTutorialFlag(tutorial: Tutorial, flag: boolean): boolean {
     const key = getDataTypeKey(GameDataType.TUTORIALS);
     let tutorials: object = {};
     if (localStorage.hasOwnProperty(key)) {
-      tutorials = JSON.parse(localStorage.getItem(key));
+      tutorials = JSON.parse(localStorage.getItem(key)!); // TODO: is this bang correct?
     }
 
     Object.keys(Tutorial).map(t => t as Tutorial).forEach(t => {
@@ -784,7 +791,7 @@ export class GameData {
       return ret;
     }
 
-    const tutorials = JSON.parse(localStorage.getItem(key));
+    const tutorials = JSON.parse(localStorage.getItem(key)!); // TODO: is this bang correct?
 
     for (const tutorial of Object.keys(tutorials)) {
       ret[tutorial] = tutorials[tutorial];
@@ -812,7 +819,7 @@ export class GameData {
       return ret;
     }
 
-    const dialogues = JSON.parse(localStorage.getItem(key));
+    const dialogues = JSON.parse(localStorage.getItem(key)!); // TODO: is this bang correct?
 
     for (const dialogue of Object.keys(dialogues)) {
       ret[dialogue] = dialogues[dialogue];
@@ -843,7 +850,7 @@ export class GameData {
     } as SessionSaveData;
   }
 
-  getSession(slotId: integer): Promise<SessionSaveData> {
+  getSession(slotId: integer): Promise<SessionSaveData | null> {
     return new Promise(async (resolve, reject) => {
       if (slotId < 0) {
         return resolve(null);
@@ -858,7 +865,7 @@ export class GameData {
         }
       };
 
-      if (!bypassLogin && !localStorage.getItem(`sessionData${slotId ? slotId : ""}_${loggedInUser.username}`)) {
+      if (!bypassLogin && !localStorage.getItem(`sessionData${slotId ? slotId : ""}_${loggedInUser?.username}`)) {
         Utils.apiFetch(`savedata/session/get?slot=${slotId}&clientSessionId=${clientSessionId}`, true)
           .then(response => response.text())
           .then(async response => {
@@ -867,12 +874,12 @@ export class GameData {
               return resolve(null);
             }
 
-            localStorage.setItem(`sessionData${slotId ? slotId : ""}_${loggedInUser.username}`, encrypt(response, bypassLogin));
+            localStorage.setItem(`sessionData${slotId ? slotId : ""}_${loggedInUser?.username}`, encrypt(response, bypassLogin));
 
             await handleSessionData(response);
           });
       } else {
-        const sessionData = localStorage.getItem(`sessionData${slotId ? slotId : ""}_${loggedInUser.username}`);
+        const sessionData = localStorage.getItem(`sessionData${slotId ? slotId : ""}_${loggedInUser?.username}`);
         if (sessionData) {
           await handleSessionData(decrypt(sessionData, bypassLogin));
         } else {
@@ -934,7 +941,7 @@ export class GameData {
 
           const battleType = sessionData.battleType || 0;
           const trainerConfig = sessionData.trainer ? trainerConfigs[sessionData.trainer.trainerType] : null;
-          const battle = scene.newBattle(sessionData.waveIndex, battleType, sessionData.trainer, battleType === BattleType.TRAINER ? trainerConfig?.doubleOnly || sessionData.trainer?.variant === TrainerVariant.DOUBLE : sessionData.enemyParty.length > 1);
+          const battle = scene.newBattle(sessionData.waveIndex, battleType, sessionData.trainer, battleType === BattleType.TRAINER ? trainerConfig?.doubleOnly || sessionData.trainer?.variant === TrainerVariant.DOUBLE : sessionData.enemyParty.length > 1)!; // TODO: is this bang correct?
           battle.enemyLevels = sessionData.enemyParty.map(p => p.level);
 
           scene.arena.init();
@@ -950,10 +957,10 @@ export class GameData {
           });
 
           scene.arena.weather = sessionData.arena.weather;
-          scene.arena.eventTarget.dispatchEvent(new WeatherChangedEvent(null, scene.arena.weather?.weatherType, scene.arena.weather?.turnsLeft));
+          scene.arena.eventTarget.dispatchEvent(new WeatherChangedEvent(WeatherType.NONE, scene.arena.weather?.weatherType!, scene.arena.weather?.turnsLeft!)); // TODO: is this bang correct?
 
           scene.arena.terrain = sessionData.arena.terrain;
-          scene.arena.eventTarget.dispatchEvent(new TerrainChangedEvent(null, scene.arena.terrain?.terrainType, scene.arena.terrain?.turnsLeft));
+          scene.arena.eventTarget.dispatchEvent(new TerrainChangedEvent(TerrainType.NONE, scene.arena.terrain?.terrainType!, scene.arena.terrain?.turnsLeft!)); // TODO: is this bang correct?
           // TODO
           //scene.arena.tags = sessionData.arena.tags;
 
@@ -983,7 +990,7 @@ export class GameData {
           initSessionFromData(sessionData);
         } else {
           this.getSession(slotId)
-            .then(data => initSessionFromData(data))
+            .then(data => data && initSessionFromData(data))
             .catch(err => {
               reject(err);
               return;
@@ -999,7 +1006,7 @@ export class GameData {
   deleteSession(slotId: integer): Promise<boolean> {
     return new Promise<boolean>(resolve => {
       if (bypassLogin) {
-        localStorage.removeItem(`sessionData${this.scene.sessionSlotId ? this.scene.sessionSlotId : ""}_${loggedInUser.username}`);
+        localStorage.removeItem(`sessionData${this.scene.sessionSlotId ? this.scene.sessionSlotId : ""}_${loggedInUser?.username}`);
         return resolve(true);
       }
 
@@ -1009,8 +1016,8 @@ export class GameData {
         }
         Utils.apiFetch(`savedata/session/delete?slot=${slotId}&clientSessionId=${clientSessionId}`, true).then(response => {
           if (response.ok) {
-            loggedInUser.lastSessionSlot = -1;
-            localStorage.removeItem(`sessionData${this.scene.sessionSlotId ? this.scene.sessionSlotId : ""}_${loggedInUser.username}`);
+            loggedInUser!.lastSessionSlot = -1; // TODO: is the bang correct?
+            localStorage.removeItem(`sessionData${this.scene.sessionSlotId ? this.scene.sessionSlotId : ""}_${loggedInUser?.username}`);
             resolve(true);
           }
           return response.text();
@@ -1040,7 +1047,7 @@ export class GameData {
 
       if (sessionData.gameMode === GameModes.DAILY) {
         if (localStorage.hasOwnProperty("daily")) {
-          daily = JSON.parse(atob(localStorage.getItem("daily")));
+          daily = JSON.parse(atob(localStorage.getItem("daily")!)); // TODO: is this bang correct?
           if (daily.includes(seed)) {
             return resolve(false);
           } else {
@@ -1062,7 +1069,7 @@ export class GameData {
   tryClearSession(scene: BattleScene, slotId: integer): Promise<[success: boolean, newClear: boolean]> {
     return new Promise<[boolean, boolean]>(resolve => {
       if (bypassLogin) {
-        localStorage.removeItem(`sessionData${slotId ? slotId : ""}_${loggedInUser.username}`);
+        localStorage.removeItem(`sessionData${slotId ? slotId : ""}_${loggedInUser?.username}`);
         return resolve([true, true]);
       }
 
@@ -1073,8 +1080,8 @@ export class GameData {
         const sessionData = this.getSessionSaveData(scene);
         Utils.apiPost(`savedata/session/clear?slot=${slotId}&trainerId=${this.trainerId}&secretId=${this.secretId}&clientSessionId=${clientSessionId}`, JSON.stringify(sessionData), undefined, true).then(response => {
           if (response.ok) {
-            loggedInUser.lastSessionSlot = -1;
-            localStorage.removeItem(`sessionData${this.scene.sessionSlotId ? this.scene.sessionSlotId : ""}_${loggedInUser.username}`);
+            loggedInUser!.lastSessionSlot = -1; // TODO: is the bang correct?
+            localStorage.removeItem(`sessionData${this.scene.sessionSlotId ? this.scene.sessionSlotId : ""}_${loggedInUser?.username}`);
           }
           return response.json();
         }).then(jsonResponse => {
@@ -1161,10 +1168,10 @@ export class GameData {
         if (sync) {
           this.scene.ui.savingIcon.show();
         }
-        const sessionData = useCachedSession ? this.parseSessionData(decrypt(localStorage.getItem(`sessionData${scene.sessionSlotId ? scene.sessionSlotId : ""}_${loggedInUser.username}`), bypassLogin)) : this.getSessionSaveData(scene);
+        const sessionData = useCachedSession ? this.parseSessionData(decrypt(localStorage.getItem(`sessionData${scene.sessionSlotId ? scene.sessionSlotId : ""}_${loggedInUser?.username}`)!, bypassLogin)) : this.getSessionSaveData(scene); // TODO: is this bang correct?
 
         const maxIntAttrValue = 0x80000000;
-        const systemData = useCachedSystem ? this.parseSystemData(decrypt(localStorage.getItem(`data_${loggedInUser.username}`), bypassLogin)) : this.getSystemSaveData();
+        const systemData = useCachedSystem ? this.parseSystemData(decrypt(localStorage.getItem(`data_${loggedInUser?.username}`)!, bypassLogin)) : this.getSystemSaveData(); // TODO: is this bang correct?
 
         const request = {
           system: systemData,
@@ -1173,9 +1180,9 @@ export class GameData {
           clientSessionId: clientSessionId
         };
 
-        localStorage.setItem(`data_${loggedInUser.username}`, encrypt(JSON.stringify(systemData, (k: any, v: any) => typeof v === "bigint" ? v <= maxIntAttrValue ? Number(v) : v.toString() : v), bypassLogin));
+        localStorage.setItem(`data_${loggedInUser?.username}`, encrypt(JSON.stringify(systemData, (k: any, v: any) => typeof v === "bigint" ? v <= maxIntAttrValue ? Number(v) : v.toString() : v), bypassLogin));
 
-        localStorage.setItem(`sessionData${scene.sessionSlotId ? scene.sessionSlotId : ""}_${loggedInUser.username}`, encrypt(JSON.stringify(sessionData), bypassLogin));
+        localStorage.setItem(`sessionData${scene.sessionSlotId ? scene.sessionSlotId : ""}_${loggedInUser?.username}`, encrypt(JSON.stringify(sessionData), bypassLogin));
 
         console.debug("Session data saved");
 
@@ -1212,7 +1219,7 @@ export class GameData {
 
   public tryExportData(dataType: GameDataType, slotId: integer = 0): Promise<boolean> {
     return new Promise<boolean>(resolve => {
-      const dataKey: string = `${getDataTypeKey(dataType, slotId)}_${loggedInUser.username}`;
+      const dataKey: string = `${getDataTypeKey(dataType, slotId)}_${loggedInUser?.username}`;
       const handleData = (dataStr: string) => {
         switch (dataType) {
         case GameDataType.SYSTEM:
@@ -1251,7 +1258,7 @@ export class GameData {
   }
 
   public importData(dataType: GameDataType, slotId: integer = 0): void {
-    const dataKey = `${getDataTypeKey(dataType, slotId)}_${loggedInUser.username}`;
+    const dataKey = `${getDataTypeKey(dataType, slotId)}_${loggedInUser?.username}`;
 
     let saveFile: any = document.getElementById("saveFile");
     if (saveFile) {
@@ -1270,7 +1277,7 @@ export class GameData {
         reader.onload = (_ => {
           return e => {
             let dataName: string;
-            let dataStr = AES.decrypt(e.target.result.toString(), saveKey).toString(enc.Utf8);
+            let dataStr = AES.decrypt(e.target?.result?.toString()!, saveKey).toString(enc.Utf8); // TODO: is this bang correct?
             let valid = false;
             try {
               dataName = GameDataType[dataType].toLowerCase();
@@ -1293,10 +1300,11 @@ export class GameData {
               console.error(ex);
             }
 
-            const displayError = (error: string) => this.scene.ui.showText(error, null, () => this.scene.ui.showText(null, 0), Utils.fixedInt(1500));
+            const displayError = (error: string) => this.scene.ui.showText(error, null, () => this.scene.ui.showText("", 0), Utils.fixedInt(1500));
+            dataName = dataName!; // tell TS compiler that dataName is defined!
 
             if (!valid) {
-              return this.scene.ui.showText(`Your ${dataName} data could not be loaded. It may be corrupted.`, null, () => this.scene.ui.showText(null, 0), Utils.fixedInt(1500));
+              return this.scene.ui.showText(`Your ${dataName} data could not be loaded. It may be corrupted.`, null, () => this.scene.ui.showText("", 0), Utils.fixedInt(1500));
             }
 
             this.scene.ui.showText(`Your ${dataName} data will be overridden and the page will reload. Proceed?`, null, () => {
@@ -1329,7 +1337,7 @@ export class GameData {
                 }
               }, () => {
                 this.scene.ui.revertMode();
-                this.scene.ui.showText(null, 0);
+                this.scene.ui.showText("", 0);
               }, false, -98);
             });
           };
@@ -1652,7 +1660,7 @@ export class GameData {
     return dexAttr & DexAttr.SHINY ? dexAttr & DexAttr.VARIANT_3 ? 3 : dexAttr & DexAttr.VARIANT_2 ? 2 : 1 : 0;
   }
 
-  getNaturesForAttr(natureAttr: integer): Nature[] {
+  getNaturesForAttr(natureAttr: integer = 0): Nature[] {
     const ret: Nature[] = [];
     for (let n = 0; n < 25; n++) {
       if (natureAttr & (1 << (n + 1))) {
@@ -1707,7 +1715,7 @@ export class GameData {
         entry.hatchedCount = 0;
       }
       if (!entry.hasOwnProperty("natureAttr") || (entry.caughtAttr && !entry.natureAttr)) {
-        entry.natureAttr = this.defaultDexData[k].natureAttr || (1 << Utils.randInt(25, 1));
+        entry.natureAttr = this.defaultDexData?.[k].natureAttr || (1 << Utils.randInt(25, 1));
       }
     }
   }
diff --git a/src/system/modifier-data.ts b/src/system/modifier-data.ts
index 6f169280da1..0f3e28fe11c 100644
--- a/src/system/modifier-data.ts
+++ b/src/system/modifier-data.ts
@@ -1,6 +1,6 @@
 import BattleScene from "../battle-scene";
 import { PersistentModifier } from "../modifier/modifier";
-import { GeneratedPersistentModifierType, ModifierTypeGenerator, getModifierTypeFuncById } from "../modifier/modifier-type";
+import { GeneratedPersistentModifierType, ModifierType, ModifierTypeGenerator, getModifierTypeFuncById } from "../modifier/modifier-type";
 
 export default class ModifierData {
   private player: boolean;
@@ -27,14 +27,14 @@ export default class ModifierData {
     this.className = sourceModifier ? sourceModifier.constructor.name : source.className;
   }
 
-  toModifier(scene: BattleScene, constructor: any): PersistentModifier {
+  toModifier(scene: BattleScene, constructor: any): PersistentModifier | null {
     const typeFunc = getModifierTypeFuncById(this.typeId);
     if (!typeFunc) {
       return null;
     }
 
     try {
-      let type = typeFunc();
+      let type: ModifierType | null = typeFunc();
       type.id = this.typeId;
 
       if (type instanceof ModifierTypeGenerator) {
diff --git a/src/system/pokemon-data.ts b/src/system/pokemon-data.ts
index ca072c9eec8..8f094379434 100644
--- a/src/system/pokemon-data.ts
+++ b/src/system/pokemon-data.ts
@@ -33,8 +33,8 @@ export default class PokemonData {
   public ivs: integer[];
   public nature: Nature;
   public natureOverride: Nature | -1;
-  public moveset: PokemonMove[];
-  public status: Status;
+  public moveset: (PokemonMove | null)[];
+  public status: Status | null;
   public friendship: integer;
   public metLevel: integer;
   public metBiome: Biome | -1;
@@ -117,7 +117,7 @@ export default class PokemonData {
       if (!forHistory) {
         this.status = source.status
           ? new Status(source.status.effect, source.status.turnCount, source.status.cureTurn)
-          : undefined;
+          : null;
       }
 
       this.summonData = new PokemonSummonData();
diff --git a/src/system/voucher.ts b/src/system/voucher.ts
index b06e6e5309e..0c71e3c0286 100644
--- a/src/system/voucher.ts
+++ b/src/system/voucher.ts
@@ -3,6 +3,7 @@ import i18next from "i18next";
 import { Achv, AchvTier, achvs, getAchievementDescription } from "./achv";
 import { PlayerGender } from "#enums/player-gender";
 import { TrainerType } from "#enums/trainer-type";
+import { ConditionFn } from "#app/@types/common.js";
 
 export enum VoucherType {
   REGULAR,
@@ -16,15 +17,15 @@ export class Voucher {
   public voucherType: VoucherType;
   public description: string;
 
-  private conditionFunc: (scene: BattleScene, args: any[]) => boolean;
+  private conditionFunc: ConditionFn | undefined;
 
-  constructor(voucherType: VoucherType, description: string, conditionFunc?: (scene: BattleScene, args: any[]) => boolean) {
+  constructor(voucherType: VoucherType, description: string, conditionFunc?: ConditionFn) {
     this.description = description;
     this.voucherType = voucherType;
     this.conditionFunc = conditionFunc;
   }
 
-  validate(scene: BattleScene, args: any[]): boolean {
+  validate(scene: BattleScene, args?: any[]): boolean {
     return !this.conditionFunc || this.conditionFunc(scene, args);
   }
 
diff --git a/src/test/abilities/battle_bond.test.ts b/src/test/abilities/battle_bond.test.ts
index ce41f9b6603..1a5c71b4c15 100644
--- a/src/test/abilities/battle_bond.test.ts
+++ b/src/test/abilities/battle_bond.test.ts
@@ -46,12 +46,12 @@ describe("Abilities - BATTLE BOND", () => {
       await game.startBattle([Species.MAGIKARP, Species.GRENINJA]);
 
       const greninja = game.scene.getParty().find((p) => p.species.speciesId === Species.GRENINJA);
-      expect(greninja).not.toBe(undefined);
-      expect(greninja.formIndex).toBe(ashForm);
+      expect(greninja).toBeDefined();
+      expect(greninja!.formIndex).toBe(ashForm);
 
-      greninja.hp = 0;
-      greninja.status = new Status(StatusEffect.FAINT);
-      expect(greninja.isFainted()).toBe(true);
+      greninja!.hp = 0;
+      greninja!.status = new Status(StatusEffect.FAINT);
+      expect(greninja!.isFainted()).toBe(true);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
       await game.doKillOpponents();
@@ -59,7 +59,7 @@ describe("Abilities - BATTLE BOND", () => {
       game.doSelectModifier();
       await game.phaseInterceptor.to(QuietFormChangePhase);
 
-      expect(greninja.formIndex).toBe(baseForm);
+      expect(greninja!.formIndex).toBe(baseForm);
     },
     TIMEOUT
   );
diff --git a/src/test/abilities/disguise.test.ts b/src/test/abilities/disguise.test.ts
index 3a6fd540d27..09a0dbf7f8a 100644
--- a/src/test/abilities/disguise.test.ts
+++ b/src/test/abilities/disguise.test.ts
@@ -47,11 +47,11 @@ describe("Abilities - DISGUISE", () => {
 
       const mimikyu = game.scene.getParty().find((p) => p.species.speciesId === Species.MIMIKYU);
       expect(mimikyu).not.toBe(undefined);
-      expect(mimikyu.formIndex).toBe(bustedForm);
+      expect(mimikyu!.formIndex).toBe(bustedForm);
 
-      mimikyu.hp = 0;
-      mimikyu.status = new Status(StatusEffect.FAINT);
-      expect(mimikyu.isFainted()).toBe(true);
+      mimikyu!.hp = 0;
+      mimikyu!.status = new Status(StatusEffect.FAINT);
+      expect(mimikyu!.isFainted()).toBe(true);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
       await game.doKillOpponents();
@@ -59,7 +59,7 @@ describe("Abilities - DISGUISE", () => {
       game.doSelectModifier();
       await game.phaseInterceptor.to(QuietFormChangePhase);
 
-      expect(mimikyu.formIndex).toBe(baseForm);
+      expect(mimikyu!.formIndex).toBe(baseForm);
     },
     TIMEOUT
   );
@@ -80,17 +80,17 @@ describe("Abilities - DISGUISE", () => {
 
       await game.startBattle([Species.MIMIKYU]);
 
-      const mimikyu = game.scene.getPlayerPokemon();
-      const damage = (Math.floor(mimikyu.getMaxHp()/8));
+      const mimikyu = game.scene.getPlayerPokemon()!;
+      const damage = (Math.floor(mimikyu!.getMaxHp()/8));
 
       expect(mimikyu).not.toBe(undefined);
-      expect(mimikyu.formIndex).toBe(baseForm);
+      expect(mimikyu!.formIndex).toBe(baseForm);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
       await game.phaseInterceptor.to(TurnEndPhase);
 
-      expect(mimikyu.formIndex).toBe(bustedForm);
-      expect(game.scene.getEnemyPokemon().turnData.currDamageDealt).toBe(damage);
+      expect(mimikyu!.formIndex).toBe(bustedForm);
+      expect(game.scene.getEnemyPokemon()!.turnData.currDamageDealt).toBe(damage);
     },
     TIMEOUT
   );
diff --git a/src/test/abilities/dry_skin.test.ts b/src/test/abilities/dry_skin.test.ts
index 6da5ad08571..20b85eab767 100644
--- a/src/test/abilities/dry_skin.test.ts
+++ b/src/test/abilities/dry_skin.test.ts
@@ -38,7 +38,7 @@ describe("Abilities - Dry Skin", () => {
 
     await game.startBattle();
 
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
     expect(enemy).not.toBe(undefined);
 
     // first turn
@@ -59,7 +59,7 @@ describe("Abilities - Dry Skin", () => {
 
     await game.startBattle();
 
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
     expect(enemy).not.toBe(undefined);
 
     enemy.hp = 1;
@@ -82,7 +82,7 @@ describe("Abilities - Dry Skin", () => {
 
     await game.startBattle();
 
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
     const initialHP = 1000;
     enemy.hp = initialHP;
 
@@ -108,7 +108,7 @@ describe("Abilities - Dry Skin", () => {
 
     await game.startBattle();
 
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
     expect(enemy).not.toBe(undefined);
 
     enemy.hp = 1;
@@ -123,7 +123,7 @@ describe("Abilities - Dry Skin", () => {
 
     await game.startBattle();
 
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
     expect(enemy).not.toBe(undefined);
 
     enemy.hp = 1;
@@ -139,7 +139,7 @@ describe("Abilities - Dry Skin", () => {
 
     await game.startBattle();
 
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
     expect(enemy).not.toBe(undefined);
 
     enemy.hp = 1;
diff --git a/src/test/abilities/gulp_missile.test.ts b/src/test/abilities/gulp_missile.test.ts
index f9329017006..b64cbe2ef10 100644
--- a/src/test/abilities/gulp_missile.test.ts
+++ b/src/test/abilities/gulp_missile.test.ts
@@ -58,7 +58,7 @@ describe("Abilities - Gulp Missile", () => {
 
   it("changes to Gulping Form if HP is over half when Surf or Dive is used", async () => {
     await game.startBattle([Species.CRAMORANT]);
-    const cramorant = game.scene.getPlayerPokemon();
+    const cramorant = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.DIVE));
     await game.toNextTurn();
@@ -72,7 +72,7 @@ describe("Abilities - Gulp Missile", () => {
 
   it("changes to Gorging Form if HP is under half when Surf or Dive is used", async () => {
     await game.startBattle([Species.CRAMORANT]);
-    const cramorant = game.scene.getPlayerPokemon();
+    const cramorant = game.scene.getPlayerPokemon()!;
 
     vi.spyOn(cramorant, "getHpRatio").mockReturnValue(.49);
     expect(cramorant.getHpRatio()).toBe(.49);
@@ -88,7 +88,7 @@ describe("Abilities - Gulp Missile", () => {
     game.override.enemyMoveset(Array(4).fill(Moves.TACKLE));
     await game.startBattle([Species.CRAMORANT]);
 
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
     vi.spyOn(enemy, "damageAndUpdate");
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.SURF));
@@ -101,7 +101,7 @@ describe("Abilities - Gulp Missile", () => {
     game.override.enemyMoveset(Array(4).fill(Moves.TAIL_WHIP));
     await game.startBattle([Species.CRAMORANT]);
 
-    const cramorant = game.scene.getPlayerPokemon();
+    const cramorant = game.scene.getPlayerPokemon()!;
     vi.spyOn(cramorant, "getHpRatio").mockReturnValue(.55);
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.SURF));
@@ -120,8 +120,8 @@ describe("Abilities - Gulp Missile", () => {
     game.override.enemyMoveset(Array(4).fill(Moves.TACKLE));
     await game.startBattle([Species.CRAMORANT]);
 
-    const cramorant = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const cramorant = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(enemy, "damageAndUpdate");
     vi.spyOn(cramorant, "getHpRatio").mockReturnValue(.55);
@@ -144,8 +144,8 @@ describe("Abilities - Gulp Missile", () => {
     game.override.enemyMoveset(Array(4).fill(Moves.TACKLE));
     await game.startBattle([Species.CRAMORANT]);
 
-    const cramorant = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const cramorant = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(enemy, "damageAndUpdate");
     vi.spyOn(cramorant, "getHpRatio").mockReturnValue(.45);
@@ -159,7 +159,7 @@ describe("Abilities - Gulp Missile", () => {
     await game.phaseInterceptor.to(TurnEndPhase);
 
     expect(enemy.damageAndUpdate).toHaveReturnedWith(getEffectDamage(enemy));
-    expect(enemy.status.effect).toBe(StatusEffect.PARALYSIS);
+    expect(enemy.status?.effect).toBe(StatusEffect.PARALYSIS);
     expect(cramorant.getTag(BattlerTagType.GULP_MISSILE_PIKACHU)).toBeUndefined();
     expect(cramorant.formIndex).toBe(NORMAL_FORM);
   });
@@ -172,7 +172,7 @@ describe("Abilities - Gulp Missile", () => {
       .enemyLevel(5);
     await game.startBattle([Species.CRAMORANT]);
 
-    const cramorant = game.scene.getPlayerPokemon();
+    const cramorant = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.DIVE));
     await game.toNextTurn();
@@ -194,8 +194,8 @@ describe("Abilities - Gulp Missile", () => {
     game.override.enemyMoveset(Array(4).fill(Moves.TACKLE)).enemyAbility(Abilities.MAGIC_GUARD);
     await game.startBattle([Species.CRAMORANT]);
 
-    const cramorant = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const cramorant = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(cramorant, "getHpRatio").mockReturnValue(.55);
 
@@ -218,7 +218,7 @@ describe("Abilities - Gulp Missile", () => {
     game.override.enemyMoveset(Array(4).fill(Moves.GASTRO_ACID));
     await game.startBattle([Species.CRAMORANT]);
 
-    const cramorant = game.scene.getPlayerPokemon();
+    const cramorant = game.scene.getPlayerPokemon()!;
     vi.spyOn(cramorant, "getHpRatio").mockReturnValue(.55);
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.SURF));
@@ -238,7 +238,7 @@ describe("Abilities - Gulp Missile", () => {
     game.override.enemyMoveset(Array(4).fill(Moves.SKILL_SWAP));
     await game.startBattle([Species.CRAMORANT]);
 
-    const cramorant = game.scene.getPlayerPokemon();
+    const cramorant = game.scene.getPlayerPokemon()!;
     vi.spyOn(cramorant, "getHpRatio").mockReturnValue(.55);
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.SURF));
@@ -261,6 +261,6 @@ describe("Abilities - Gulp Missile", () => {
     game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
     await game.phaseInterceptor.to(TurnStartPhase);
 
-    expect(game.scene.getEnemyPokemon().hasAbility(Abilities.GULP_MISSILE)).toBe(false);
+    expect(game.scene.getEnemyPokemon()?.hasAbility(Abilities.GULP_MISSILE)).toBe(false);
   });
 });
diff --git a/src/test/abilities/hustle.test.ts b/src/test/abilities/hustle.test.ts
index 63e54dfb157..4434dc62a6b 100644
--- a/src/test/abilities/hustle.test.ts
+++ b/src/test/abilities/hustle.test.ts
@@ -38,7 +38,7 @@ describe("Abilities - Hustle", () => {
 
   it("increases the user's Attack stat by 50%", async () => {
     await game.startBattle([Species.PIKACHU]);
-    const pikachu = game.scene.getPlayerPokemon();
+    const pikachu = game.scene.getPlayerPokemon()!;
     const atk = pikachu.stats[Stat.ATK];
 
     vi.spyOn(pikachu, "getBattleStat");
@@ -53,7 +53,7 @@ describe("Abilities - Hustle", () => {
 
   it("lowers the accuracy of the user's physical moves by 20%", async () => {
     await game.startBattle([Species.PIKACHU]);
-    const pikachu = game.scene.getPlayerPokemon();
+    const pikachu = game.scene.getPlayerPokemon()!;
 
     vi.spyOn(pikachu, "getAccuracyMultiplier");
 
@@ -65,7 +65,7 @@ describe("Abilities - Hustle", () => {
 
   it("does not affect non-physical moves", async () => {
     await game.startBattle([Species.PIKACHU]);
-    const pikachu = game.scene.getPlayerPokemon();
+    const pikachu = game.scene.getPlayerPokemon()!;
     const spatk = pikachu.stats[Stat.SPATK];
 
     vi.spyOn(pikachu, "getBattleStat");
@@ -83,8 +83,8 @@ describe("Abilities - Hustle", () => {
     game.override.enemyLevel(30);
 
     await game.startBattle([Species.PIKACHU]);
-    const pikachu = game.scene.getPlayerPokemon();
-    const enemyPokemon = game.scene.getEnemyPokemon();
+    const pikachu = game.scene.getPlayerPokemon()!;
+    const enemyPokemon = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(pikachu, "getAccuracyMultiplier");
     vi.spyOn(allMoves[Moves.FISSURE], "calculateBattleAccuracy");
diff --git a/src/test/abilities/ice_face.test.ts b/src/test/abilities/ice_face.test.ts
index a08a6a01b60..cdf8d5928ee 100644
--- a/src/test/abilities/ice_face.test.ts
+++ b/src/test/abilities/ice_face.test.ts
@@ -40,11 +40,11 @@ describe("Abilities - Ice Face", () => {
 
     await game.phaseInterceptor.to(MoveEndPhase);
 
-    const eiscue = game.scene.getEnemyPokemon();
+    const eiscue = game.scene.getEnemyPokemon()!;
 
     expect(eiscue.isFullHp()).toBe(true);
     expect(eiscue.formIndex).toBe(noiceForm);
-    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBe(undefined);
+    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBeUndefined();
   });
 
   it("takes no damage from the first hit of multihit physical move and transforms to Noice", async () => {
@@ -54,7 +54,7 @@ describe("Abilities - Ice Face", () => {
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.SURGING_STRIKES));
 
-    const eiscue = game.scene.getEnemyPokemon();
+    const eiscue = game.scene.getEnemyPokemon()!;
     expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBeDefined();
 
     // First hit
@@ -82,7 +82,7 @@ describe("Abilities - Ice Face", () => {
 
     await game.phaseInterceptor.to(MoveEndPhase);
 
-    const eiscue = game.scene.getEnemyPokemon();
+    const eiscue = game.scene.getEnemyPokemon()!;
 
     expect(eiscue.getTag(BattlerTagType.ICE_FACE)).not.toBe(undefined);
     expect(eiscue.formIndex).toBe(icefaceForm);
@@ -96,7 +96,7 @@ describe("Abilities - Ice Face", () => {
 
     await game.phaseInterceptor.to(MoveEndPhase);
 
-    const eiscue = game.scene.getEnemyPokemon();
+    const eiscue = game.scene.getEnemyPokemon()!;
 
     expect(eiscue.getTag(BattlerTagType.ICE_FACE)).not.toBe(undefined);
     expect(eiscue.formIndex).toBe(icefaceForm);
@@ -112,15 +112,15 @@ describe("Abilities - Ice Face", () => {
 
     await game.phaseInterceptor.to(MoveEndPhase);
 
-    const eiscue = game.scene.getEnemyPokemon();
+    const eiscue = game.scene.getEnemyPokemon()!;
 
     expect(eiscue.isFullHp()).toBe(true);
     expect(eiscue.formIndex).toBe(noiceForm);
-    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBe(undefined);
+    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBeUndefined();
 
     await game.phaseInterceptor.to(MoveEndPhase);
 
-    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).not.toBe(undefined);
+    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).not.toBeNull();
     expect(eiscue.formIndex).toBe(icefaceForm);
   });
 
@@ -133,9 +133,9 @@ describe("Abilities - Ice Face", () => {
     game.doAttack(getMovePosition(game.scene, 0, Moves.SNOWSCAPE));
 
     await game.phaseInterceptor.to(TurnEndPhase);
-    let eiscue = game.scene.getPlayerPokemon();
+    let eiscue = game.scene.getPlayerPokemon()!;
 
-    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBe(undefined);
+    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBeUndefined();
     expect(eiscue.formIndex).toBe(noiceForm);
     expect(eiscue.isFullHp()).toBe(true);
 
@@ -145,7 +145,7 @@ describe("Abilities - Ice Face", () => {
     game.doSwitchPokemon(1);
 
     await game.phaseInterceptor.to(QuietFormChangePhase);
-    eiscue = game.scene.getPlayerPokemon();
+    eiscue = game.scene.getPlayerPokemon()!;
 
     expect(eiscue.formIndex).toBe(icefaceForm);
     expect(eiscue.getTag(BattlerTagType.ICE_FACE)).not.toBe(undefined);
@@ -158,17 +158,17 @@ describe("Abilities - Ice Face", () => {
     await game.startBattle([Species.EISCUE]);
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.HAIL));
-    const eiscue = game.scene.getPlayerPokemon();
+    const eiscue = game.scene.getPlayerPokemon()!;
 
     await game.phaseInterceptor.to(QuietFormChangePhase);
 
     expect(eiscue.formIndex).toBe(noiceForm);
-    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBe(undefined);
+    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBeUndefined();
 
     await game.phaseInterceptor.to(TurnEndPhase);
 
     expect(eiscue.formIndex).toBe(noiceForm);
-    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBe(undefined);
+    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBeUndefined();
   });
 
   it("persists form change when switched out", async () => {
@@ -179,9 +179,9 @@ describe("Abilities - Ice Face", () => {
     game.doAttack(getMovePosition(game.scene, 0, Moves.ICE_BEAM));
 
     await game.phaseInterceptor.to(TurnEndPhase);
-    let eiscue = game.scene.getPlayerPokemon();
+    let eiscue = game.scene.getPlayerPokemon()!;
 
-    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBe(undefined);
+    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBeUndefined();
     expect(eiscue.formIndex).toBe(noiceForm);
     expect(eiscue.isFullHp()).toBe(true);
 
@@ -192,7 +192,7 @@ describe("Abilities - Ice Face", () => {
     eiscue = game.scene.getParty()[1];
 
     expect(eiscue.formIndex).toBe(noiceForm);
-    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBe(undefined);
+    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBeUndefined();
   });
 
   it("reverts to Ice Face on arena reset", async () => {
@@ -205,10 +205,10 @@ describe("Abilities - Ice Face", () => {
 
     await game.startBattle([Species.EISCUE]);
 
-    const eiscue = game.scene.getPlayerPokemon();
+    const eiscue = game.scene.getPlayerPokemon()!;
 
     expect(eiscue.formIndex).toBe(noiceForm);
-    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBe(undefined);
+    expect(eiscue.getTag(BattlerTagType.ICE_FACE)).toBeUndefined();
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.ICE_BEAM));
     await game.doKillOpponents();
@@ -229,7 +229,7 @@ describe("Abilities - Ice Face", () => {
 
     await game.phaseInterceptor.to(TurnEndPhase);
 
-    const eiscue = game.scene.getEnemyPokemon();
+    const eiscue = game.scene.getEnemyPokemon()!;
 
     expect(eiscue.getTag(BattlerTagType.ICE_FACE)).not.toBe(undefined);
     expect(eiscue.formIndex).toBe(icefaceForm);
@@ -245,7 +245,7 @@ describe("Abilities - Ice Face", () => {
 
     await game.phaseInterceptor.to(TurnEndPhase);
 
-    const eiscue = game.scene.getEnemyPokemon();
+    const eiscue = game.scene.getEnemyPokemon()!;
 
     expect(eiscue.getTag(BattlerTagType.ICE_FACE)).not.toBe(undefined);
     expect(eiscue.formIndex).toBe(icefaceForm);
@@ -261,10 +261,10 @@ describe("Abilities - Ice Face", () => {
 
     await game.phaseInterceptor.to(TurnInitPhase);
 
-    const eiscue = game.scene.getEnemyPokemon();
+    const eiscue = game.scene.getEnemyPokemon()!;
 
     expect(eiscue.getTag(BattlerTagType.ICE_FACE)).not.toBe(undefined);
     expect(eiscue.formIndex).toBe(icefaceForm);
-    expect(game.scene.getPlayerPokemon().hasAbility(Abilities.TRACE)).toBe(true);
+    expect(game.scene.getPlayerPokemon()!.hasAbility(Abilities.TRACE)).toBe(true);
   });
 });
diff --git a/src/test/abilities/libero.test.ts b/src/test/abilities/libero.test.ts
index c38ec082169..e4d99d5b56c 100644
--- a/src/test/abilities/libero.test.ts
+++ b/src/test/abilities/libero.test.ts
@@ -46,7 +46,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
@@ -64,7 +64,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP, Species.BULBASAUR]);
 
-      let leadPokemon = game.scene.getPlayerPokemon();
+      let leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
@@ -86,7 +86,7 @@ describe("Abilities - Protean", () => {
       game.doSwitchPokemon(1);
       await game.toNextTurn();
 
-      leadPokemon = game.scene.getPlayerPokemon();
+      leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
@@ -104,7 +104,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.scene.arena.weather = new Weather(WeatherType.SUNNY);
@@ -128,7 +128,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -150,7 +150,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.scene.arena.biomeType = Biome.MOUNTAIN;
@@ -169,7 +169,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.DIG));
@@ -188,7 +188,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -196,7 +196,7 @@ describe("Abilities - Protean", () => {
       vi.spyOn(game.scene.getCurrentPhase() as MoveEffectPhase, "hitCheck").mockReturnValueOnce(false);
       await game.phaseInterceptor.to(TurnEndPhase);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon.isFullHp()).toBe(true);
       testPokemonTypeMatchesDefaultMoveType(leadPokemon, Moves.TACKLE);
     },
@@ -211,7 +211,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -230,7 +230,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -248,7 +248,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       leadPokemon.summonData.types = [allMoves[Moves.SPLASH].defaultType];
@@ -267,7 +267,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       vi.spyOn(leadPokemon, "isTerastallized").mockReturnValue(true);
@@ -287,7 +287,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.STRUGGLE));
@@ -305,7 +305,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.BURN_UP));
@@ -324,7 +324,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TRICK_OR_TREAT));
@@ -342,7 +342,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.CURSE));
diff --git a/src/test/abilities/magic_guard.test.ts b/src/test/abilities/magic_guard.test.ts
index 18e28284f72..23b3bad828f 100644
--- a/src/test/abilities/magic_guard.test.ts
+++ b/src/test/abilities/magic_guard.test.ts
@@ -53,9 +53,10 @@ describe("Abilities - Magic Guard", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
+      expect(enemyPokemon).toBeDefined();
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
 
@@ -79,7 +80,7 @@ describe("Abilities - Magic Guard", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
 
@@ -91,7 +92,7 @@ describe("Abilities - Magic Guard", () => {
        * - The Pokemon's CatchRateMultiplier should be 1.5
        */
       expect(leadPokemon.hp).toBe(leadPokemon.getMaxHp());
-      expect(getStatusEffectCatchRateMultiplier(leadPokemon.status.effect)).toBe(1.5);
+      expect(getStatusEffectCatchRateMultiplier(leadPokemon.status!.effect)).toBe(1.5);
     }, TIMEOUT
   );
 
@@ -103,7 +104,7 @@ describe("Abilities - Magic Guard", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
 
@@ -127,7 +128,7 @@ describe("Abilities - Magic Guard", () => {
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       await game.phaseInterceptor.to(TurnEndPhase);
 
@@ -138,7 +139,7 @@ describe("Abilities - Magic Guard", () => {
        * - The enemy Pokemon's hypothetical CatchRateMultiplier should be 1.5
        */
       expect(enemyPokemon.hp).toBe(enemyPokemon.getMaxHp());
-      expect(getStatusEffectCatchRateMultiplier(enemyPokemon.status.effect)).toBe(1.5);
+      expect(getStatusEffectCatchRateMultiplier(enemyPokemon.status!.effect)).toBe(1.5);
     }, TIMEOUT
   );
 
@@ -151,9 +152,9 @@ describe("Abilities - Magic Guard", () => {
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
-      const toxicStartCounter = enemyPokemon.status.turnCount;
+      const toxicStartCounter = enemyPokemon.status!.turnCount;
       //should be 0
 
       await game.phaseInterceptor.to(TurnEndPhase);
@@ -165,23 +166,23 @@ describe("Abilities - Magic Guard", () => {
        * - The enemy Pokemon's hypothetical CatchRateMultiplier should be 1.5
        */
       expect(enemyPokemon.hp).toBe(enemyPokemon.getMaxHp());
-      expect(enemyPokemon.status.turnCount).toBeGreaterThan(toxicStartCounter);
-      expect(getStatusEffectCatchRateMultiplier(enemyPokemon.status.effect)).toBe(1.5);
+      expect(enemyPokemon.status!.turnCount).toBeGreaterThan(toxicStartCounter);
+      expect(getStatusEffectCatchRateMultiplier(enemyPokemon.status!.effect)).toBe(1.5);
     }, TIMEOUT
   );
 
 
   it("Magic Guard prevents damage caused by entry hazards", async () => {
     //Adds and applies Spikes to both sides of the arena
-    const newTag = getArenaTag(ArenaTagType.SPIKES, 5, Moves.SPIKES, 0, 0, ArenaTagSide.BOTH);
+    const newTag = getArenaTag(ArenaTagType.SPIKES, 5, Moves.SPIKES, 0, 0, ArenaTagSide.BOTH)!;
     game.scene.arena.tags.push(newTag);
 
     await game.startBattle([Species.MAGIKARP]);
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
 
-    const enemyPokemon = game.scene.getEnemyPokemon();
+    const enemyPokemon = game.scene.getEnemyPokemon()!;
 
     await game.phaseInterceptor.to(TurnEndPhase);
 
@@ -197,17 +198,17 @@ describe("Abilities - Magic Guard", () => {
 
   it("Magic Guard does not prevent poison from Toxic Spikes", async () => {
     //Adds and applies Spikes to both sides of the arena
-    const playerTag = getArenaTag(ArenaTagType.TOXIC_SPIKES, 5, Moves.TOXIC_SPIKES, 0, 0, ArenaTagSide.PLAYER);
-    const enemyTag = getArenaTag(ArenaTagType.TOXIC_SPIKES, 5, Moves.TOXIC_SPIKES, 0, 0, ArenaTagSide.ENEMY);
+    const playerTag = getArenaTag(ArenaTagType.TOXIC_SPIKES, 5, Moves.TOXIC_SPIKES, 0, 0, ArenaTagSide.PLAYER)!;
+    const enemyTag = getArenaTag(ArenaTagType.TOXIC_SPIKES, 5, Moves.TOXIC_SPIKES, 0, 0, ArenaTagSide.ENEMY)!;
     game.scene.arena.tags.push(playerTag);
     game.scene.arena.tags.push(enemyTag);
 
     await game.startBattle([Species.MAGIKARP]);
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
 
-    const enemyPokemon = game.scene.getEnemyPokemon();
+    const enemyPokemon = game.scene.getEnemyPokemon()!;
 
     await game.phaseInterceptor.to(TurnEndPhase);
 
@@ -217,8 +218,8 @@ describe("Abilities - Magic Guard", () => {
     * - The player Pokemon (with Magic Guard) has not taken damage from poison
     * - The enemy Pokemon (without Magic Guard) has taken damage from poison
     */
-    expect(leadPokemon.status.effect).toBe(StatusEffect.POISON);
-    expect(enemyPokemon.status.effect).toBe(StatusEffect.POISON);
+    expect(leadPokemon.status!.effect).toBe(StatusEffect.POISON);
+    expect(enemyPokemon.status!.effect).toBe(StatusEffect.POISON);
     expect(leadPokemon.hp).toBe(leadPokemon.getMaxHp());
     expect(enemyPokemon.hp).toBeLessThan(enemyPokemon.getMaxHp());
   }, TIMEOUT
@@ -230,11 +231,11 @@ describe("Abilities - Magic Guard", () => {
       game.override.moveset([Moves.CURSE]);
       game.override.enemyAbility(Abilities.MAGIC_GUARD);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.CURSE));
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       await game.phaseInterceptor.to(TurnEndPhase);
 
@@ -254,7 +255,7 @@ describe("Abilities - Magic Guard", () => {
     game.override.moveset([Moves.HIGH_JUMP_KICK]);
     await game.startBattle([Species.MAGIKARP]);
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.HIGH_JUMP_KICK));
     await game.phaseInterceptor.to(MoveEffectPhase, false);
@@ -274,7 +275,7 @@ describe("Abilities - Magic Guard", () => {
     game.override.moveset([Moves.TAKE_DOWN]);
     await game.startBattle([Species.MAGIKARP]);
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.TAKE_DOWN));
 
@@ -292,7 +293,7 @@ describe("Abilities - Magic Guard", () => {
     game.override.moveset([Moves.STRUGGLE]);
     await game.startBattle([Species.MAGIKARP]);
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.STRUGGLE));
 
@@ -311,7 +312,7 @@ describe("Abilities - Magic Guard", () => {
     game.override.moveset([Moves.STEEL_BEAM]);
     await game.startBattle([Species.MAGIKARP]);
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.STEEL_BEAM));
 
@@ -339,7 +340,7 @@ describe("Abilities - Magic Guard", () => {
     game.override.moveset([Moves.BELLY_DRUM]);
     await game.startBattle([Species.MAGIKARP]);
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.BELLY_DRUM));
 
@@ -362,7 +363,7 @@ describe("Abilities - Magic Guard", () => {
 
     await game.startBattle([Species.MAGIKARP]);
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
 
@@ -374,7 +375,7 @@ describe("Abilities - Magic Guard", () => {
     * - The player Pokemon is asleep
     */
     expect(leadPokemon.hp).toBe(leadPokemon.getMaxHp());
-    expect(leadPokemon.status.effect).toBe(StatusEffect.SLEEP);
+    expect(leadPokemon.status!.effect).toBe(StatusEffect.SLEEP);
   }, TIMEOUT
   );
 
@@ -385,9 +386,9 @@ describe("Abilities - Magic Guard", () => {
 
     await game.startBattle([Species.MAGIKARP]);
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
-    const enemyPokemon = game.scene.getEnemyPokemon();
+    const enemyPokemon = game.scene.getEnemyPokemon()!;
     enemyPokemon.hp = 1;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -410,9 +411,9 @@ describe("Abilities - Magic Guard", () => {
 
     await game.startBattle([Species.MAGIKARP]);
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
-    const enemyPokemon = game.scene.getEnemyPokemon();
+    const enemyPokemon = game.scene.getEnemyPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
     await game.phaseInterceptor.to(TurnEndPhase);
@@ -434,9 +435,9 @@ describe("Abilities - Magic Guard", () => {
 
     await game.startBattle([Species.MAGIKARP]);
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
-    const enemyPokemon = game.scene.getEnemyPokemon();
+    const enemyPokemon = game.scene.getEnemyPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.ABSORB));
     await game.phaseInterceptor.to(TurnEndPhase);
@@ -457,7 +458,7 @@ describe("Abilities - Magic Guard", () => {
     game.override.weather(WeatherType.SUNNY);
 
     await game.startBattle([Species.MAGIKARP]);
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
     game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
     await game.phaseInterceptor.to(TurnEndPhase);
 
diff --git a/src/test/abilities/parental_bond.test.ts b/src/test/abilities/parental_bond.test.ts
index 45d65fca083..1fb27ad7e1f 100644
--- a/src/test/abilities/parental_bond.test.ts
+++ b/src/test/abilities/parental_bond.test.ts
@@ -47,10 +47,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       let enemyStartingHp = enemyPokemon.hp;
@@ -80,10 +80,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.POWER_UP_PUNCH));
@@ -102,10 +102,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.BABY_DOLL_EYES));
@@ -122,10 +122,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.DOUBLE_HIT));
@@ -147,10 +147,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SELF_DESTRUCT));
@@ -168,10 +168,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.ROLLOUT));
@@ -192,10 +192,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       const enemyStartingHp = enemyPokemon.hp;
@@ -215,10 +215,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       const playerStartingHp = leadPokemon.hp;
@@ -268,10 +268,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.EARTHQUAKE));
@@ -288,10 +288,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.PIDGEOT]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.MIND_BLOWN));
@@ -314,10 +314,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.BURN_UP));
@@ -342,10 +342,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -364,10 +364,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       const enemyStartingHp = enemyPokemon.hp;
@@ -395,10 +395,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       const enemyStartingHp = enemyPokemon.hp;
@@ -425,10 +425,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.HYPER_BEAM));
@@ -455,10 +455,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.ANCHOR_SHOT));
@@ -487,10 +487,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SMACK_DOWN));
@@ -516,10 +516,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD, Species.BLASTOISE]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.U_TURN));
@@ -542,10 +542,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.WAKE_UP_SLAP));
@@ -572,10 +572,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -594,10 +594,10 @@ describe("Abilities - Parental Bond", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.WATER_GUN));
diff --git a/src/test/abilities/pastel_veil.test.ts b/src/test/abilities/pastel_veil.test.ts
index 8035d54a7e5..e3d52a720b3 100644
--- a/src/test/abilities/pastel_veil.test.ts
+++ b/src/test/abilities/pastel_veil.test.ts
@@ -51,7 +51,7 @@ describe("Abilities - Pastel Veil", () => {
 
   it("it heals the poisoned status condition of allies if user is sent out into battle", async () => {
     await game.startBattle([Species.MAGIKARP, Species.MAGIKARP, Species.GALAR_PONYTA]);
-    const ponyta = game.scene.getParty().find(p => p.species.speciesId === Species.GALAR_PONYTA);
+    const ponyta = game.scene.getParty().find(p => p.species.speciesId === Species.GALAR_PONYTA)!;
 
     vi.spyOn(ponyta, "getAbility").mockReturnValue(allAbilities[Abilities.PASTEL_VEIL]);
 
@@ -66,7 +66,7 @@ describe("Abilities - Pastel Veil", () => {
     const poisonedMon = game.scene.getPlayerField().find(p => p.status?.effect === StatusEffect.POISON);
 
     await game.phaseInterceptor.to(CommandPhase);
-    game.doAttack(getMovePosition(game.scene, (poisonedMon.getBattlerIndex() as BattlerIndex.PLAYER | BattlerIndex.PLAYER_2), Moves.SPLASH));
+    game.doAttack(getMovePosition(game.scene, (poisonedMon!.getBattlerIndex() as BattlerIndex.PLAYER | BattlerIndex.PLAYER_2), Moves.SPLASH));
     game.doSwitchPokemon(2);
     await game.phaseInterceptor.to(TurnEndPhase);
 
diff --git a/src/test/abilities/power_construct.test.ts b/src/test/abilities/power_construct.test.ts
index 769499c0e53..dd8fd836e51 100644
--- a/src/test/abilities/power_construct.test.ts
+++ b/src/test/abilities/power_construct.test.ts
@@ -47,11 +47,11 @@ describe("Abilities - POWER CONSTRUCT", () => {
 
       const zygarde = game.scene.getParty().find((p) => p.species.speciesId === Species.ZYGARDE);
       expect(zygarde).not.toBe(undefined);
-      expect(zygarde.formIndex).toBe(completeForm);
+      expect(zygarde!.formIndex).toBe(completeForm);
 
-      zygarde.hp = 0;
-      zygarde.status = new Status(StatusEffect.FAINT);
-      expect(zygarde.isFainted()).toBe(true);
+      zygarde!.hp = 0;
+      zygarde!.status = new Status(StatusEffect.FAINT);
+      expect(zygarde!.isFainted()).toBe(true);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
       await game.doKillOpponents();
@@ -59,7 +59,7 @@ describe("Abilities - POWER CONSTRUCT", () => {
       game.doSelectModifier();
       await game.phaseInterceptor.to(QuietFormChangePhase);
 
-      expect(zygarde.formIndex).toBe(baseForm);
+      expect(zygarde!.formIndex).toBe(baseForm);
     },
     TIMEOUT
   );
diff --git a/src/test/abilities/protean.test.ts b/src/test/abilities/protean.test.ts
index 7c6cca2eccd..63d1a0ea719 100644
--- a/src/test/abilities/protean.test.ts
+++ b/src/test/abilities/protean.test.ts
@@ -46,7 +46,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
@@ -64,7 +64,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP, Species.BULBASAUR]);
 
-      let leadPokemon = game.scene.getPlayerPokemon();
+      let leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
@@ -86,7 +86,7 @@ describe("Abilities - Protean", () => {
       game.doSwitchPokemon(1);
       await game.toNextTurn();
 
-      leadPokemon = game.scene.getPlayerPokemon();
+      leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
@@ -104,7 +104,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.scene.arena.weather = new Weather(WeatherType.SUNNY);
@@ -128,7 +128,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -150,7 +150,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.scene.arena.biomeType = Biome.MOUNTAIN;
@@ -169,7 +169,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.DIG));
@@ -188,7 +188,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -196,7 +196,7 @@ describe("Abilities - Protean", () => {
       vi.spyOn(game.scene.getCurrentPhase() as MoveEffectPhase, "hitCheck").mockReturnValueOnce(false);
       await game.phaseInterceptor.to(TurnEndPhase);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       expect(enemyPokemon.isFullHp()).toBe(true);
       testPokemonTypeMatchesDefaultMoveType(leadPokemon, Moves.TACKLE);
     },
@@ -211,7 +211,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -230,7 +230,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TACKLE));
@@ -248,7 +248,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       leadPokemon.summonData.types = [allMoves[Moves.SPLASH].defaultType];
@@ -267,7 +267,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       vi.spyOn(leadPokemon, "isTerastallized").mockReturnValue(true);
@@ -287,7 +287,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.STRUGGLE));
@@ -305,7 +305,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.BURN_UP));
@@ -324,7 +324,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.TRICK_OR_TREAT));
@@ -342,7 +342,7 @@ describe("Abilities - Protean", () => {
 
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       expect(leadPokemon).not.toBe(undefined);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.CURSE));
diff --git a/src/test/abilities/quick_draw.test.ts b/src/test/abilities/quick_draw.test.ts
index 56f21cab838..75bb9ec6a0a 100644
--- a/src/test/abilities/quick_draw.test.ts
+++ b/src/test/abilities/quick_draw.test.ts
@@ -41,8 +41,8 @@ describe("Abilities - Quick Draw", () => {
   test("makes pokemon going first in its priority bracket", async () => {
     await game.startBattle();
 
-    const pokemon = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const pokemon = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     pokemon.hp = 1;
     enemy.hp = 1;
@@ -61,8 +61,8 @@ describe("Abilities - Quick Draw", () => {
   }, async () => {
     await game.startBattle();
 
-    const pokemon = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const pokemon = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     pokemon.hp = 1;
     enemy.hp = 1;
@@ -81,8 +81,8 @@ describe("Abilities - Quick Draw", () => {
 
     await game.startBattle();
 
-    const pokemon = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const pokemon = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     pokemon.hp = 1;
     enemy.hp = 1;
diff --git a/src/test/abilities/sand_spit.test.ts b/src/test/abilities/sand_spit.test.ts
index dacfe7ad27e..d3d1a8e0028 100644
--- a/src/test/abilities/sand_spit.test.ts
+++ b/src/test/abilities/sand_spit.test.ts
@@ -42,7 +42,7 @@ describe("Ability Timing", () => {
     game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
     await game.toNextTurn();
 
-    expect(game.scene.arena.weather.weatherType).toBe(WeatherType.SANDSTORM);
+    expect(game.scene.arena.weather?.weatherType).toBe(WeatherType.SANDSTORM);
   }, 20000);
 
   it("should not trigger when targetted with status moves", async() => {
diff --git a/src/test/abilities/sap_sipper.test.ts b/src/test/abilities/sap_sipper.test.ts
index 20a677a3244..6fbe57978e9 100644
--- a/src/test/abilities/sap_sipper.test.ts
+++ b/src/test/abilities/sap_sipper.test.ts
@@ -87,7 +87,7 @@ describe("Abilities - Sap Sipper", () => {
     await game.phaseInterceptor.to(TurnEndPhase);
 
     expect(game.scene.arena.terrain).toBeDefined();
-    expect(game.scene.arena.terrain.terrainType).toBe(TerrainType.GRASSY);
+    expect(game.scene.arena.terrain!.terrainType).toBe(TerrainType.GRASSY);
     expect(game.scene.getEnemyParty()[0].summonData.battleStats[BattleStat.ATK]).toBe(0);
   });
 
diff --git a/src/test/abilities/schooling.test.ts b/src/test/abilities/schooling.test.ts
index 7671534a549..e55b7795006 100644
--- a/src/test/abilities/schooling.test.ts
+++ b/src/test/abilities/schooling.test.ts
@@ -45,7 +45,7 @@ describe("Abilities - SCHOOLING", () => {
 
       await game.startBattle([Species.MAGIKARP, Species.WISHIWASHI]);
 
-      const wishiwashi = game.scene.getParty().find((p) => p.species.speciesId === Species.WISHIWASHI);
+      const wishiwashi = game.scene.getParty().find((p) => p.species.speciesId === Species.WISHIWASHI)!;
       expect(wishiwashi).not.toBe(undefined);
       expect(wishiwashi.formIndex).toBe(schoolForm);
 
diff --git a/src/test/abilities/serene_grace.test.ts b/src/test/abilities/serene_grace.test.ts
index 3e8ff0bbea0..c486604e4f9 100644
--- a/src/test/abilities/serene_grace.test.ts
+++ b/src/test/abilities/serene_grace.test.ts
@@ -66,8 +66,8 @@ describe("Abilities - Serene Grace", () => {
     expect(move.id).toBe(Moves.AIR_SLASH);
 
     const chance = new Utils.IntegerHolder(move.chance);
-    console.log(move.chance + " Their ability is " + phase.getUserPokemon().getAbility().name);
-    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon(), null, chance, move, phase.getTarget(), false);
+    console.log(move.chance + " Their ability is " + phase.getUserPokemon()!.getAbility().name);
+    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon()!, null, chance, move, phase.getTarget(), false);
     expect(chance.value).toBe(30);
 
   }, 20000);
@@ -99,7 +99,7 @@ describe("Abilities - Serene Grace", () => {
     expect(move.id).toBe(Moves.AIR_SLASH);
 
     const chance = new Utils.IntegerHolder(move.chance);
-    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon(), null, chance, move, phase.getTarget(), false);
+    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon()!, null, chance, move, phase.getTarget(), false);
     expect(chance.value).toBe(60);
 
   }, 20000);
diff --git a/src/test/abilities/sheer_force.test.ts b/src/test/abilities/sheer_force.test.ts
index d3e1ae904cc..3f1bcadd43f 100644
--- a/src/test/abilities/sheer_force.test.ts
+++ b/src/test/abilities/sheer_force.test.ts
@@ -69,8 +69,8 @@ describe("Abilities - Sheer Force", () => {
     const power = new Utils.IntegerHolder(move.power);
     const chance = new Utils.IntegerHolder(move.chance);
 
-    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon(), null, chance, move, phase.getTarget(), false);
-    applyPreAttackAbAttrs(MovePowerBoostAbAttr, phase.getUserPokemon(), phase.getTarget(), move, power);
+    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon()!, null, chance, move, phase.getTarget(), false);
+    applyPreAttackAbAttrs(MovePowerBoostAbAttr, phase.getUserPokemon()!, phase.getTarget()!, move, power);
 
     expect(chance.value).toBe(0);
     expect(power.value).toBe(move.power * 5461/4096);
@@ -108,8 +108,8 @@ describe("Abilities - Sheer Force", () => {
     const power = new Utils.IntegerHolder(move.power);
     const chance = new Utils.IntegerHolder(move.chance);
 
-    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon(), null, chance, move, phase.getTarget(), false);
-    applyPreAttackAbAttrs(MovePowerBoostAbAttr, phase.getUserPokemon(), phase.getTarget(), move, power);
+    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon()!, null, chance, move, phase.getTarget(), false);
+    applyPreAttackAbAttrs(MovePowerBoostAbAttr, phase.getUserPokemon()!, phase.getTarget()!, move, power);
 
     expect(chance.value).toBe(-1);
     expect(power.value).toBe(move.power);
@@ -147,8 +147,8 @@ describe("Abilities - Sheer Force", () => {
     const power = new Utils.IntegerHolder(move.power);
     const chance = new Utils.IntegerHolder(move.chance);
 
-    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon(), null, chance, move, phase.getTarget(), false);
-    applyPreAttackAbAttrs(MovePowerBoostAbAttr, phase.getUserPokemon(), phase.getTarget(), move, power);
+    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon()!, null, chance, move, phase.getTarget(), false);
+    applyPreAttackAbAttrs(MovePowerBoostAbAttr, phase.getUserPokemon()!, phase.getTarget()!, move, power);
 
     expect(chance.value).toBe(-1);
     expect(power.value).toBe(move.power);
@@ -187,8 +187,8 @@ describe("Abilities - Sheer Force", () => {
     //Disable color change due to being hit by Sheer Force
     const power = new Utils.IntegerHolder(move.power);
     const chance = new Utils.IntegerHolder(move.chance);
-    const user = phase.getUserPokemon();
-    const target = phase.getTarget();
+    const user = phase.getUserPokemon()!;
+    const target = phase.getTarget()!;
     const opponentType = target.getTypes()[0];
 
     applyAbAttrs(MoveEffectChanceMultiplierAbAttr, user, null, chance, move, target, false);
diff --git a/src/test/abilities/shield_dust.test.ts b/src/test/abilities/shield_dust.test.ts
index f6906cb7b85..c7e62b333d7 100644
--- a/src/test/abilities/shield_dust.test.ts
+++ b/src/test/abilities/shield_dust.test.ts
@@ -67,8 +67,8 @@ describe("Abilities - Shield Dust", () => {
     expect(move.id).toBe(Moves.AIR_SLASH);
 
     const chance = new Utils.IntegerHolder(move.chance);
-    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon(), null, chance, move, phase.getTarget(), false);
-    applyPreDefendAbAttrs(IgnoreMoveEffectsAbAttr, phase.getTarget(),phase.getUserPokemon(),null,null, chance);
+    applyAbAttrs(MoveEffectChanceMultiplierAbAttr, phase.getUserPokemon()!, null, chance, move, phase.getTarget(), false);
+    applyPreDefendAbAttrs(IgnoreMoveEffectsAbAttr, phase.getTarget()!, phase.getUserPokemon()!, null!, null!, chance);
     expect(chance.value).toBe(0);
 
   }, 20000);
diff --git a/src/test/abilities/shields_down.test.ts b/src/test/abilities/shields_down.test.ts
index 64904c80032..4d85e8aa47c 100644
--- a/src/test/abilities/shields_down.test.ts
+++ b/src/test/abilities/shields_down.test.ts
@@ -45,7 +45,7 @@ describe("Abilities - SHIELDS DOWN", () => {
 
       await game.startBattle([Species.MAGIKARP, Species.MINIOR]);
 
-      const minior = game.scene.getParty().find((p) => p.species.speciesId === Species.MINIOR);
+      const minior = game.scene.getParty().find((p) => p.species.speciesId === Species.MINIOR)!;
       expect(minior).not.toBe(undefined);
       expect(minior.formIndex).toBe(coreForm);
 
diff --git a/src/test/abilities/steely_spirit.test.ts b/src/test/abilities/steely_spirit.test.ts
index e21067539df..5d5514bc3a1 100644
--- a/src/test/abilities/steely_spirit.test.ts
+++ b/src/test/abilities/steely_spirit.test.ts
@@ -40,7 +40,7 @@ describe("Abilities - Steely Spirit", () => {
   it("increases Steel-type moves' power used by the user and its allies by 50%", async () => {
     await game.startBattle([Species.PIKACHU, Species.SHUCKLE]);
     const boostSource = game.scene.getPlayerField()[1];
-    const enemyToCheck = game.scene.getEnemyPokemon();
+    const enemyToCheck = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(boostSource, "getAbility").mockReturnValue(allAbilities[Abilities.STEELY_SPIRIT]);
 
@@ -57,7 +57,7 @@ describe("Abilities - Steely Spirit", () => {
 
   it("stacks if multiple users with this ability are on the field.", async () => {
     await game.startBattle([Species.PIKACHU, Species.PIKACHU]);
-    const enemyToCheck = game.scene.getEnemyPokemon();
+    const enemyToCheck = game.scene.getEnemyPokemon()!;
 
     game.scene.getPlayerField().forEach(p => {
       vi.spyOn(p, "getAbility").mockReturnValue(allAbilities[Abilities.STEELY_SPIRIT]);
@@ -79,7 +79,7 @@ describe("Abilities - Steely Spirit", () => {
   it("does not take effect when suppressed", async () => {
     await game.startBattle([Species.PIKACHU, Species.SHUCKLE]);
     const boostSource = game.scene.getPlayerField()[1];
-    const enemyToCheck = game.scene.getEnemyPokemon();
+    const enemyToCheck = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(boostSource, "getAbility").mockReturnValue(allAbilities[Abilities.STEELY_SPIRIT]);
     expect(boostSource.hasAbility(Abilities.STEELY_SPIRIT)).toBe(true);
diff --git a/src/test/abilities/sweet_veil.test.ts b/src/test/abilities/sweet_veil.test.ts
index 19c1210b443..03e9452a358 100644
--- a/src/test/abilities/sweet_veil.test.ts
+++ b/src/test/abilities/sweet_veil.test.ts
@@ -92,7 +92,7 @@ describe("Abilities - Sweet Veil", () => {
 
     await game.phaseInterceptor.to(TurnEndPhase);
 
-    const drowsyMon = game.scene.getPlayerField().find(p => !!p.getTag(BattlerTagType.DROWSY));
+    const drowsyMon = game.scene.getPlayerField().find(p => !!p.getTag(BattlerTagType.DROWSY))!;
 
     await game.phaseInterceptor.to(CommandPhase);
     game.doAttack(getMovePosition(game.scene, (drowsyMon.getBattlerIndex() as BattlerIndex.PLAYER | BattlerIndex.PLAYER_2), Moves.SPLASH));
diff --git a/src/test/abilities/unseen_fist.test.ts b/src/test/abilities/unseen_fist.test.ts
index 0ee4dbef513..a6cad8b03ce 100644
--- a/src/test/abilities/unseen_fist.test.ts
+++ b/src/test/abilities/unseen_fist.test.ts
@@ -72,10 +72,10 @@ async function testUnseenFistHitResult(game: GameManager, attackMove: Moves, pro
 
   await game.startBattle();
 
-  const leadPokemon = game.scene.getPlayerPokemon();
+  const leadPokemon = game.scene.getPlayerPokemon()!;
   expect(leadPokemon).not.toBe(undefined);
 
-  const enemyPokemon = game.scene.getEnemyPokemon();
+  const enemyPokemon = game.scene.getEnemyPokemon()!;
   expect(enemyPokemon).not.toBe(undefined);
 
   const enemyStartingHp = enemyPokemon.hp;
diff --git a/src/test/abilities/wind_power.test.ts b/src/test/abilities/wind_power.test.ts
index 8a4c2969cc4..670544a89ef 100644
--- a/src/test/abilities/wind_power.test.ts
+++ b/src/test/abilities/wind_power.test.ts
@@ -34,7 +34,7 @@ describe("Abilities - Wind Power", () => {
 
   it("it becomes charged when hit by wind moves", async () => {
     await game.startBattle([Species.MAGIKARP]);
-    const shiftry = game.scene.getEnemyPokemon();
+    const shiftry = game.scene.getEnemyPokemon()!;
 
     expect(shiftry.getTag(BattlerTagType.CHARGED)).toBeUndefined();
 
@@ -49,7 +49,7 @@ describe("Abilities - Wind Power", () => {
     game.override.enemySpecies(Species.MAGIKARP);
 
     await game.startBattle([Species.SHIFTRY]);
-    const shiftry = game.scene.getPlayerPokemon();
+    const shiftry = game.scene.getPlayerPokemon()!;
 
     expect(shiftry.getTag(BattlerTagType.CHARGED)).toBeUndefined();
 
@@ -64,8 +64,8 @@ describe("Abilities - Wind Power", () => {
     game.override.ability(Abilities.WIND_POWER);
 
     await game.startBattle([Species.SHIFTRY]);
-    const magikarp = game.scene.getEnemyPokemon();
-    const shiftry = game.scene.getPlayerPokemon();
+    const magikarp = game.scene.getEnemyPokemon()!;
+    const shiftry = game.scene.getPlayerPokemon()!;
 
     expect(shiftry.getTag(BattlerTagType.CHARGED)).toBeUndefined();
     expect(magikarp.getTag(BattlerTagType.CHARGED)).toBeUndefined();
@@ -82,7 +82,7 @@ describe("Abilities - Wind Power", () => {
     game.override.enemySpecies(Species.MAGIKARP);
 
     await game.startBattle([Species.SHIFTRY]);
-    const shiftry = game.scene.getPlayerPokemon();
+    const shiftry = game.scene.getPlayerPokemon()!;
 
     expect(shiftry.getTag(BattlerTagType.CHARGED)).toBeUndefined();
 
diff --git a/src/test/abilities/wind_rider.test.ts b/src/test/abilities/wind_rider.test.ts
index 855def63b6f..e27349efe41 100644
--- a/src/test/abilities/wind_rider.test.ts
+++ b/src/test/abilities/wind_rider.test.ts
@@ -34,7 +34,7 @@ describe("Abilities - Wind Rider", () => {
 
   it("takes no damage from wind moves and its Attack is increased by one stage when hit by one", async () => {
     await game.startBattle([Species.MAGIKARP]);
-    const shiftry = game.scene.getEnemyPokemon();
+    const shiftry = game.scene.getEnemyPokemon()!;
 
     expect(shiftry.summonData.battleStats[BattleStat.ATK]).toBe(0);
 
@@ -51,7 +51,7 @@ describe("Abilities - Wind Rider", () => {
     game.override.enemySpecies(Species.MAGIKARP);
 
     await game.startBattle([Species.SHIFTRY]);
-    const shiftry = game.scene.getPlayerPokemon();
+    const shiftry = game.scene.getPlayerPokemon()!;
 
     expect(shiftry.summonData.battleStats[BattleStat.ATK]).toBe(0);
 
@@ -67,8 +67,8 @@ describe("Abilities - Wind Rider", () => {
     game.override.enemySpecies(Species.MAGIKARP);
 
     await game.startBattle([Species.SHIFTRY]);
-    const magikarp = game.scene.getEnemyPokemon();
-    const shiftry = game.scene.getPlayerPokemon();
+    const magikarp = game.scene.getEnemyPokemon()!;
+    const shiftry = game.scene.getPlayerPokemon()!;
 
     expect(shiftry.summonData.battleStats[BattleStat.ATK]).toBe(0);
     expect(magikarp.summonData.battleStats[BattleStat.ATK]).toBe(0);
@@ -85,8 +85,8 @@ describe("Abilities - Wind Rider", () => {
     game.override.enemySpecies(Species.MAGIKARP);
 
     await game.startBattle([Species.SHIFTRY]);
-    const magikarp = game.scene.getEnemyPokemon();
-    const shiftry = game.scene.getPlayerPokemon();
+    const magikarp = game.scene.getEnemyPokemon()!;
+    const shiftry = game.scene.getPlayerPokemon()!;
 
     expect(shiftry.summonData.battleStats[BattleStat.ATK]).toBe(0);
     expect(magikarp.summonData.battleStats[BattleStat.ATK]).toBe(0);
@@ -103,7 +103,7 @@ describe("Abilities - Wind Rider", () => {
     game.override.enemySpecies(Species.MAGIKARP);
 
     await game.startBattle([Species.SHIFTRY]);
-    const shiftry = game.scene.getPlayerPokemon();
+    const shiftry = game.scene.getPlayerPokemon()!;
 
     expect(shiftry.summonData.battleStats[BattleStat.ATK]).toBe(0);
     expect(shiftry.isFullHp()).toBe(true);
diff --git a/src/test/abilities/zen_mode.test.ts b/src/test/abilities/zen_mode.test.ts
index 01d3724825c..63c6a3d4acf 100644
--- a/src/test/abilities/zen_mode.test.ts
+++ b/src/test/abilities/zen_mode.test.ts
@@ -150,7 +150,7 @@ describe("Abilities - ZEN MODE", () => {
 
       await game.startBattle([Species.MAGIKARP, Species.DARMANITAN]);
 
-      const darmanitan = game.scene.getParty().find((p) => p.species.speciesId === Species.DARMANITAN);
+      const darmanitan = game.scene.getParty().find((p) => p.species.speciesId === Species.DARMANITAN)!;
       expect(darmanitan).not.toBe(undefined);
       expect(darmanitan.formIndex).toBe(zenForm);
 
diff --git a/src/test/abilities/zero_to_hero.test.ts b/src/test/abilities/zero_to_hero.test.ts
index 409fb35a78c..c58761ce621 100644
--- a/src/test/abilities/zero_to_hero.test.ts
+++ b/src/test/abilities/zero_to_hero.test.ts
@@ -45,7 +45,7 @@ describe("Abilities - ZERO TO HERO", () => {
 
       await game.startBattle([Species.MAGIKARP, Species.PALAFIN]);
 
-      const palafin = game.scene.getParty().find((p) => p.species.speciesId === Species.PALAFIN);
+      const palafin = game.scene.getParty().find((p) => p.species.speciesId === Species.PALAFIN)!;
       expect(palafin).not.toBe(undefined);
       expect(palafin.formIndex).toBe(heroForm);
 
diff --git a/src/test/account.spec.ts b/src/test/account.spec.ts
index 28e48ce9933..d5d0458c7e8 100644
--- a/src/test/account.spec.ts
+++ b/src/test/account.spec.ts
@@ -8,21 +8,21 @@ describe("account", () => {
     it("should set loggedInUser to Guest and lastSessionSlot to -1", () => {
       initLoggedInUser();
 
-      expect(loggedInUser.username).toBe("Guest");
-      expect(loggedInUser.lastSessionSlot).toBe(-1);
+      expect(loggedInUser!.username).toBe("Guest");
+      expect(loggedInUser!.lastSessionSlot).toBe(-1);
     });
   });
 
   describe("updateUserInfo", () => {
-    it("should set loggedInUser to Guest if bypassLogin is true", async () => {
+    it("should set loggedInUser! to Guest if bypassLogin is true", async () => {
       vi.spyOn(battleScene, "bypassLogin", "get").mockReturnValue(true);
 
       const [success, status] = await updateUserInfo();
 
       expect(success).toBe(true);
       expect(status).toBe(200);
-      expect(loggedInUser.username).toBe("Guest");
-      expect(loggedInUser.lastSessionSlot).toBe(-1);
+      expect(loggedInUser!.username).toBe("Guest");
+      expect(loggedInUser!.lastSessionSlot).toBe(-1);
     });
 
     it("should fetch user info from the API if bypassLogin is false", async () => {
@@ -43,8 +43,8 @@ describe("account", () => {
 
       expect(success).toBe(true);
       expect(status).toBe(200);
-      expect(loggedInUser.username).toBe("test");
-      expect(loggedInUser.lastSessionSlot).toBe(99);
+      expect(loggedInUser!.username).toBe("test");
+      expect(loggedInUser!.lastSessionSlot).toBe(99);
     });
 
     it("should handle resolved API errors", async () => {
diff --git a/src/test/achievements/achievement.test.ts b/src/test/achievements/achievement.test.ts
index 14466a71086..5cd9c4d4094 100644
--- a/src/test/achievements/achievement.test.ts
+++ b/src/test/achievements/achievement.test.ts
@@ -3,12 +3,12 @@ import { Achv, AchvTier, DamageAchv, HealAchv, LevelAchv, ModifierAchv, MoneyAch
 import GameManager from "#test/utils/gameManager";
 import { IntegerHolder, NumberHolder } from "#app/utils.js";
 import Phaser from "phaser";
-import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
 import BattleScene from "../../battle-scene";
 
 describe("check some Achievement related stuff", () => {
   it ("should check Achievement creation", () => {
-    const ach = new MoneyAchv("", "Achievement", 1000, null, 100);
+    const ach = new MoneyAchv("", "Achievement", 1000, null!, 100);
     expect(ach.name).toBe("Achievement");
   });
 });
@@ -58,7 +58,7 @@ describe("Achv", () => {
   });
 
   it("should validate the achievement based on the condition function", () => {
-    const conditionFunc = jest.fn((scene: BattleScene, args: any[]) => args[0] === 10);
+    const conditionFunc = vi.fn((scene: BattleScene, args: any[]) => args[0] === 10);
     const achv = new Achv("", "Test Achievement", "Test Description", "test_icon", 10, conditionFunc);
 
     expect(achv.validate(new BattleScene(), [5])).toBe(false);
@@ -196,7 +196,7 @@ describe("ModifierAchv", () => {
   it("should validate the achievement based on the modifier function", () => {
     const modifierAchv = new ModifierAchv("", "Test Modifier Achievement", "Test Description", "modifier_icon", 10, () => true);
     const scene = new BattleScene();
-    const modifier = new TurnHeldItemTransferModifier(null, 3, 1);
+    const modifier = new TurnHeldItemTransferModifier(null!, 3, 1);
 
     expect(modifierAchv.validate(scene, [modifier])).toBe(true);
   });
diff --git a/src/test/arena/weather_strong_winds.test.ts b/src/test/arena/weather_strong_winds.test.ts
index 0fd45173033..d9f626cfb83 100644
--- a/src/test/arena/weather_strong_winds.test.ts
+++ b/src/test/arena/weather_strong_winds.test.ts
@@ -35,8 +35,8 @@ describe("Weather - Strong Winds", () => {
     game.override.enemySpecies(Species.RAYQUAZA);
 
     await game.startBattle([Species.PIKACHU]);
-    const pikachu = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const pikachu = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.THUNDERBOLT));
 
@@ -46,8 +46,8 @@ describe("Weather - Strong Winds", () => {
 
   it("electric type move is neutral for flying type pokemon", async () => {
     await game.startBattle([Species.PIKACHU]);
-    const pikachu = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const pikachu = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.THUNDERBOLT));
 
@@ -57,8 +57,8 @@ describe("Weather - Strong Winds", () => {
 
   it("ice type move is neutral for flying type pokemon", async () => {
     await game.startBattle([Species.PIKACHU]);
-    const pikachu = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const pikachu = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.ICE_BEAM));
 
@@ -68,8 +68,8 @@ describe("Weather - Strong Winds", () => {
 
   it("rock type move is neutral for flying type pokemon", async () => {
     await game.startBattle([Species.PIKACHU]);
-    const pikachu = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const pikachu = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.ROCK_SLIDE));
 
diff --git a/src/test/battle/battle.test.ts b/src/test/battle/battle.test.ts
index 21b890d9cf0..a4713f90506 100644
--- a/src/test/battle/battle.test.ts
+++ b/src/test/battle/battle.test.ts
@@ -90,7 +90,7 @@ describe("Test Battle Phase", () => {
   it("newGame one-liner", async() => {
     await game.startBattle();
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("do attack wave 3 - single battle - regular - OHKO", async() => {
@@ -218,7 +218,7 @@ describe("Test Battle Phase", () => {
       Species.CHARIZARD,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("1vs1", async() => {
@@ -230,7 +230,7 @@ describe("Test Battle Phase", () => {
       Species.BLASTOISE,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("2vs2", async() => {
@@ -244,7 +244,7 @@ describe("Test Battle Phase", () => {
       Species.CHARIZARD,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("4vs2", async() => {
@@ -260,7 +260,7 @@ describe("Test Battle Phase", () => {
       Species.GABITE,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("kill opponent pokemon", async() => {
@@ -342,7 +342,7 @@ describe("Test Battle Phase", () => {
       .startingHeldItems([{ name: "TEMP_STAT_BOOSTER", type: TempBattleStat.ACC }]);
 
     await game.startBattle();
-    game.scene.getPlayerPokemon().hp = 1;
+    game.scene.getPlayerPokemon()!.hp = 1;
     game.doAttack(getMovePosition(game.scene, 0, moveToUse));
 
     await game.phaseInterceptor.to(BattleEndPhase);
diff --git a/src/test/battle/special_battle.test.ts b/src/test/battle/special_battle.test.ts
index b8a29e82f69..6130df703f5 100644
--- a/src/test/battle/special_battle.test.ts
+++ b/src/test/battle/special_battle.test.ts
@@ -40,7 +40,7 @@ describe("Test Battle Phase", () => {
       Species.CHARIZARD,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("startBattle 2vs2 boss", async() => {
@@ -52,7 +52,7 @@ describe("Test Battle Phase", () => {
       Species.CHARIZARD,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("startBattle 2vs2 trainer", async() => {
@@ -64,7 +64,7 @@ describe("Test Battle Phase", () => {
       Species.CHARIZARD,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("startBattle 2vs1 trainer", async() => {
@@ -76,7 +76,7 @@ describe("Test Battle Phase", () => {
       Species.CHARIZARD,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("startBattle 2vs1 rival", async() => {
@@ -88,7 +88,7 @@ describe("Test Battle Phase", () => {
       Species.CHARIZARD,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("startBattle 2vs2 rival", async() => {
@@ -100,7 +100,7 @@ describe("Test Battle Phase", () => {
       Species.CHARIZARD,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("startBattle 1vs1 trainer", async() => {
@@ -111,7 +111,7 @@ describe("Test Battle Phase", () => {
       Species.BLASTOISE,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("startBattle 2vs2 trainer", async() => {
@@ -123,7 +123,7 @@ describe("Test Battle Phase", () => {
       Species.CHARIZARD,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 
   it("startBattle 4vs2 trainer", async() => {
@@ -137,7 +137,7 @@ describe("Test Battle Phase", () => {
       Species.GABITE,
     ]);
     expect(game.scene.ui?.getMode()).toBe(Mode.COMMAND);
-    expect(game.scene.getCurrentPhase().constructor.name).toBe(CommandPhase.name);
+    expect(game.scene.getCurrentPhase()!.constructor.name).toBe(CommandPhase.name);
   }, 20000);
 });
 
diff --git a/src/test/battlerTags/octolock.test.ts b/src/test/battlerTags/octolock.test.ts
index 4c1c58d4345..369a84e21fa 100644
--- a/src/test/battlerTags/octolock.test.ts
+++ b/src/test/battlerTags/octolock.test.ts
@@ -6,7 +6,7 @@ import { StatChangePhase } from "#app/phases.js";
 import { BattleStat } from "#app/data/battle-stat.js";
 import { BattlerTagType } from "#app/enums/battler-tag-type.js";
 
-jest.mock("#app/battle-scene.js");
+vi.mock("#app/battle-scene.js");
 
 describe("BattlerTag - OctolockTag", () => {
   describe("lapse behavior", () => {
@@ -49,7 +49,7 @@ describe("BattlerTag - OctolockTag", () => {
 
   it("cannot be added to pokemon who are octolocked", { timeout: 2000 }, async => {
     const mockPokemon = {
-      getTag: vi.fn().mockReturnValue(new BattlerTag(null, null, null, null)) as Pokemon["getTag"],
+      getTag: vi.fn().mockReturnValue(new BattlerTag(null!, null!, null!, null!)) as Pokemon["getTag"],
     } as Pokemon;
 
     const subject = new OctolockTag(1);
diff --git a/src/test/battlerTags/stockpiling.test.ts b/src/test/battlerTags/stockpiling.test.ts
index 5cf07c47ce1..005f1e1593c 100644
--- a/src/test/battlerTags/stockpiling.test.ts
+++ b/src/test/battlerTags/stockpiling.test.ts
@@ -27,7 +27,7 @@ describe("BattlerTag - StockpilingTag", () => {
         expect((phase as StatChangePhase)["levels"]).toEqual(1);
         expect((phase as StatChangePhase)["stats"]).toEqual(expect.arrayContaining([BattleStat.DEF, BattleStat.SPDEF]));
 
-        (phase as StatChangePhase)["onChange"](mockPokemon, [BattleStat.DEF, BattleStat.SPDEF], [1, 1]);
+        (phase as StatChangePhase)["onChange"]!(mockPokemon, [BattleStat.DEF, BattleStat.SPDEF], [1, 1]);
       });
 
       subject.onAdd(mockPokemon);
@@ -54,7 +54,7 @@ describe("BattlerTag - StockpilingTag", () => {
         expect((phase as StatChangePhase)["levels"]).toEqual(1);
         expect((phase as StatChangePhase)["stats"]).toEqual(expect.arrayContaining([BattleStat.DEF, BattleStat.SPDEF]));
 
-        (phase as StatChangePhase)["onChange"](mockPokemon, [BattleStat.DEF, BattleStat.SPDEF], [1, 1]);
+        (phase as StatChangePhase)["onChange"]!(mockPokemon, [BattleStat.DEF, BattleStat.SPDEF], [1, 1]);
       });
 
       subject.onAdd(mockPokemon);
@@ -79,7 +79,7 @@ describe("BattlerTag - StockpilingTag", () => {
         expect((phase as StatChangePhase)["levels"]).toEqual(1);
         expect((phase as StatChangePhase)["stats"]).toEqual(expect.arrayContaining([BattleStat.DEF, BattleStat.SPDEF]));
 
-        (phase as StatChangePhase)["onChange"](mockPokemon, [BattleStat.DEF, BattleStat.SPDEF], [1, 1]);
+        (phase as StatChangePhase)["onChange"]!(mockPokemon, [BattleStat.DEF, BattleStat.SPDEF], [1, 1]);
       });
 
       subject.onOverlap(mockPokemon);
@@ -109,7 +109,7 @@ describe("BattlerTag - StockpilingTag", () => {
         expect((phase as StatChangePhase)["stats"]).toEqual(expect.arrayContaining([BattleStat.DEF, BattleStat.SPDEF]));
 
         // def doesn't change
-        (phase as StatChangePhase)["onChange"](mockPokemon, [BattleStat.SPDEF], [1]);
+        (phase as StatChangePhase)["onChange"]!(mockPokemon, [BattleStat.SPDEF], [1]);
       });
 
       subject.onAdd(mockPokemon);
@@ -121,7 +121,7 @@ describe("BattlerTag - StockpilingTag", () => {
         expect((phase as StatChangePhase)["stats"]).toEqual(expect.arrayContaining([BattleStat.DEF, BattleStat.SPDEF]));
 
         // def doesn't change
-        (phase as StatChangePhase)["onChange"](mockPokemon, [BattleStat.SPDEF], [1]);
+        (phase as StatChangePhase)["onChange"]!(mockPokemon, [BattleStat.SPDEF], [1]);
       });
 
       subject.onOverlap(mockPokemon);
diff --git a/src/test/evolution.test.ts b/src/test/evolution.test.ts
index acb012741ff..c8ebffa6119 100644
--- a/src/test/evolution.test.ts
+++ b/src/test/evolution.test.ts
@@ -64,7 +64,7 @@ describe("Evolution", () => {
   it("should handle illegal abilityIndex values", async () => {
     await game.runToSummon([Species.SQUIRTLE]);
 
-    const squirtle = game.scene.getPlayerPokemon();
+    const squirtle = game.scene.getPlayerPokemon()!;
     squirtle.abilityIndex = 5;
 
     squirtle.evolve(pokemonEvolutions[Species.SQUIRTLE][0], squirtle.getSpeciesForm());
@@ -74,7 +74,7 @@ describe("Evolution", () => {
   it("should handle nincada's unique evolution", async () => {
     await game.runToSummon([Species.NINCADA]);
 
-    const nincada = game.scene.getPlayerPokemon();
+    const nincada = game.scene.getPlayerPokemon()!;
     nincada.abilityIndex = 2;
 
     nincada.evolve(pokemonEvolutions[Species.NINCADA][0], nincada.getSpeciesForm());
diff --git a/src/test/evolutions/evolutions.test.ts b/src/test/evolutions/evolutions.test.ts
index e6e9e0d56e2..af43e91b059 100644
--- a/src/test/evolutions/evolutions.test.ts
+++ b/src/test/evolutions/evolutions.test.ts
@@ -34,14 +34,14 @@ describe("Evolution tests", () => {
      * 1, 2 or 3, it's a 4 family maushold
      */
     await game.startBattle([Species.TANDEMAUS]); // starts us off with a tandemaus
-    const playerPokemon = game.scene.getPlayerPokemon();
+    const playerPokemon = game.scene.getPlayerPokemon()!;
     playerPokemon.level = 25; // tandemaus evolves at level 25
     vi.spyOn(Utils, "randSeedInt").mockReturnValue(0); // setting the random generator to be 0 to force a three family maushold
-    const threeForm = playerPokemon.getEvolution();
+    const threeForm = playerPokemon.getEvolution()!;
     expect(threeForm.evoFormKey).toBe("three"); // as per pokemon-forms, the evoFormKey for 3 family mausholds is "three"
     for (let f = 1; f < 4; f++) {
       vi.spyOn(Utils, "randSeedInt").mockReturnValue(f); // setting the random generator to 1, 2 and 3 to force 4 family mausholds
-      const fourForm = playerPokemon.getEvolution();
+      const fourForm = playerPokemon.getEvolution()!;
       expect(fourForm.evoFormKey).toBe(null); // meanwhile, according to the pokemon-forms, the evoFormKey for a 4 family maushold is null
     }
   }, 5000);
diff --git a/src/test/field/pokemon.test.ts b/src/test/field/pokemon.test.ts
new file mode 100644
index 00000000000..2220a6f613e
--- /dev/null
+++ b/src/test/field/pokemon.test.ts
@@ -0,0 +1,31 @@
+import { Species } from "#app/enums/species.js";
+import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
+import GameManager from "../utils/gameManager";
+
+describe("Spec - Pokemon", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+  });
+
+  it("should not crash when trying to set status of undefined", async () => {
+    await game.runToSummon([Species.ABRA]);
+
+    const pkm = game.scene.getPlayerPokemon()!;
+    expect(pkm).toBeDefined();
+
+    expect(pkm.trySetStatus(undefined)).toBe(true);
+  });
+});
diff --git a/src/test/final_boss.test.ts b/src/test/final_boss.test.ts
index bc950e45767..c087bd5ba82 100644
--- a/src/test/final_boss.test.ts
+++ b/src/test/final_boss.test.ts
@@ -35,7 +35,7 @@ describe("Final Boss", () => {
 
     expect(game.scene.currentBattle.waveIndex).toBe(FinalWave.Classic);
     expect(game.scene.arena.biomeType).toBe(Biome.END);
-    expect(game.scene.getEnemyPokemon().species.speciesId).toBe(Species.ETERNATUS);
+    expect(game.scene.getEnemyPokemon()!.species.speciesId).toBe(Species.ETERNATUS);
   });
 
   it("should NOT spawn Eternatus before wave 200 in END biome", async () => {
@@ -44,7 +44,7 @@ describe("Final Boss", () => {
 
     expect(game.scene.currentBattle.waveIndex).not.toBe(FinalWave.Classic);
     expect(game.scene.arena.biomeType).toBe(Biome.END);
-    expect(game.scene.getEnemyPokemon().species.speciesId).not.toBe(Species.ETERNATUS);
+    expect(game.scene.getEnemyPokemon()!.species.speciesId).not.toBe(Species.ETERNATUS);
   });
 
   it("should NOT spawn Eternatus outside of END biome", async () => {
@@ -53,7 +53,7 @@ describe("Final Boss", () => {
 
     expect(game.scene.currentBattle.waveIndex).toBe(FinalWave.Classic);
     expect(game.scene.arena.biomeType).not.toBe(Biome.END);
-    expect(game.scene.getEnemyPokemon().species.speciesId).not.toBe(Species.ETERNATUS);
+    expect(game.scene.getEnemyPokemon()!.species.speciesId).not.toBe(Species.ETERNATUS);
   });
 
   it.todo("should change form on direct hit down to last boss fragment", () => {});
diff --git a/src/test/internals.test.ts b/src/test/internals.test.ts
index 2ada42d0c8c..d186849830d 100644
--- a/src/test/internals.test.ts
+++ b/src/test/internals.test.ts
@@ -24,7 +24,7 @@ describe("Internals", () => {
 
   it("should provide Eevee with 3 defined abilities", async () => {
     await game.runToSummon([Species.EEVEE]);
-    const eevee = game.scene.getPlayerPokemon();
+    const eevee = game.scene.getPlayerPokemon()!;
 
     expect(eevee.getSpeciesForm().getAbilityCount()).toBe(3);
 
@@ -35,7 +35,7 @@ describe("Internals", () => {
 
   it("should set Eeeve abilityIndex between 0-2", async () => {
     await game.runToSummon([Species.EEVEE]);
-    const eevee = game.scene.getPlayerPokemon();
+    const eevee = game.scene.getPlayerPokemon()!;
 
     expect(eevee.abilityIndex).toBeGreaterThanOrEqual(0);
     expect(eevee.abilityIndex).toBeLessThanOrEqual(2);
diff --git a/src/test/items/exp_booster.test.ts b/src/test/items/exp_booster.test.ts
index 7ea457eda1f..3348304b2e7 100644
--- a/src/test/items/exp_booster.test.ts
+++ b/src/test/items/exp_booster.test.ts
@@ -31,7 +31,7 @@ describe("EXP Modifier Items", () => {
     game.override.startingHeldItems([{name: "LUCKY_EGG"}, {name: "GOLDEN_EGG"}]);
     await game.startBattle();
 
-    const partyMember = game.scene.getPlayerPokemon();
+    const partyMember = game.scene.getPlayerPokemon()!;
     const modifierBonusExp = new Utils.NumberHolder(1);
     partyMember.scene.applyModifiers(PokemonExpBoosterModifier, true, partyMember, modifierBonusExp);
     expect(modifierBonusExp.value).toBe(2.4);
diff --git a/src/test/items/leek.test.ts b/src/test/items/leek.test.ts
index 8532f0df8d9..2cfd4d8dc64 100644
--- a/src/test/items/leek.test.ts
+++ b/src/test/items/leek.test.ts
@@ -56,7 +56,7 @@ describe("Items - Leek", () => {
       Species.FARFETCHD
     ]);
 
-    const partyMember = game.scene.getPlayerPokemon();
+    const partyMember = game.scene.getPlayerPokemon()!;
 
     // Making sure modifier is not applied without holding item
     const critLevel = new Utils.IntegerHolder(0);
@@ -76,7 +76,7 @@ describe("Items - Leek", () => {
       Species.GALAR_FARFETCHD
     ]);
 
-    const partyMember = game.scene.getPlayerPokemon();
+    const partyMember = game.scene.getPlayerPokemon()!;
 
     // Making sure modifier is not applied without holding item
     const critLevel = new Utils.IntegerHolder(0);
@@ -96,7 +96,7 @@ describe("Items - Leek", () => {
       Species.SIRFETCHD
     ]);
 
-    const partyMember = game.scene.getPlayerPokemon();
+    const partyMember = game.scene.getPlayerPokemon()!;
 
     // Making sure modifier is not applied without holding item
     const critLevel = new Utils.IntegerHolder(0);
@@ -186,7 +186,7 @@ describe("Items - Leek", () => {
       Species.PIKACHU
     ]);
 
-    const partyMember = game.scene.getPlayerPokemon();
+    const partyMember = game.scene.getPlayerPokemon()!;
 
     // Making sure modifier is not applied without holding item
     const critLevel = new Utils.IntegerHolder(0);
diff --git a/src/test/items/leftovers.test.ts b/src/test/items/leftovers.test.ts
index 6850528a664..e791c4426a1 100644
--- a/src/test/items/leftovers.test.ts
+++ b/src/test/items/leftovers.test.ts
@@ -40,7 +40,7 @@ describe("Items - Leftovers", () => {
     // Make sure leftovers are there
     expect(game.scene.modifiers[0].type.id).toBe("LEFTOVERS");
 
-    const leadPokemon = game.scene.getPlayerPokemon();
+    const leadPokemon = game.scene.getPlayerPokemon()!;
 
     // We should have full hp
     expect(leadPokemon.isFullHp()).toBe(true);
diff --git a/src/test/items/light_ball.test.ts b/src/test/items/light_ball.test.ts
index fef5793d26c..ff7dfa4eba5 100644
--- a/src/test/items/light_ball.test.ts
+++ b/src/test/items/light_ball.test.ts
@@ -83,7 +83,7 @@ describe("Items - Light Ball", () => {
     expect(spAtkValue.value / spAtkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["LIGHT_BALL"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["LIGHT_BALL"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.SPATK, spAtkValue);
 
@@ -122,7 +122,7 @@ describe("Items - Light Ball", () => {
     expect(spAtkValue.value / spAtkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["LIGHT_BALL"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["LIGHT_BALL"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.SPATK, spAtkValue);
 
@@ -161,7 +161,7 @@ describe("Items - Light Ball", () => {
     expect(spAtkValue.value / spAtkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["LIGHT_BALL"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["LIGHT_BALL"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.SPATK, spAtkValue);
 
@@ -189,7 +189,7 @@ describe("Items - Light Ball", () => {
     expect(spAtkValue.value / spAtkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["LIGHT_BALL"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["LIGHT_BALL"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.SPATK, spAtkValue);
 
diff --git a/src/test/items/metal_powder.test.ts b/src/test/items/metal_powder.test.ts
index da5d9109c9a..966762e4175 100644
--- a/src/test/items/metal_powder.test.ts
+++ b/src/test/items/metal_powder.test.ts
@@ -79,7 +79,7 @@ describe("Items - Metal Powder", () => {
     expect(defValue.value / defStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["METAL_POWDER"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["METAL_POWDER"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.DEF, defValue);
 
     expect(defValue.value / defStat).toBe(2);
@@ -112,7 +112,7 @@ describe("Items - Metal Powder", () => {
     expect(defValue.value / defStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["METAL_POWDER"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["METAL_POWDER"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.DEF, defValue);
 
     expect(defValue.value / defStat).toBe(2);
@@ -145,7 +145,7 @@ describe("Items - Metal Powder", () => {
     expect(defValue.value / defStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["METAL_POWDER"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["METAL_POWDER"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.DEF, defValue);
 
     expect(defValue.value / defStat).toBe(2);
@@ -167,7 +167,7 @@ describe("Items - Metal Powder", () => {
     expect(defValue.value / defStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["METAL_POWDER"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["METAL_POWDER"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.DEF, defValue);
 
     expect(defValue.value / defStat).toBe(1);
diff --git a/src/test/items/quick_powder.test.ts b/src/test/items/quick_powder.test.ts
index 939d25070bc..d2435dab431 100644
--- a/src/test/items/quick_powder.test.ts
+++ b/src/test/items/quick_powder.test.ts
@@ -79,7 +79,7 @@ describe("Items - Quick Powder", () => {
     expect(spdValue.value / spdStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["QUICK_POWDER"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["QUICK_POWDER"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.SPD, spdValue);
 
     expect(spdValue.value / spdStat).toBe(2);
@@ -112,7 +112,7 @@ describe("Items - Quick Powder", () => {
     expect(spdValue.value / spdStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["QUICK_POWDER"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["QUICK_POWDER"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.SPD, spdValue);
 
     expect(spdValue.value / spdStat).toBe(2);
@@ -145,7 +145,7 @@ describe("Items - Quick Powder", () => {
     expect(spdValue.value / spdStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["QUICK_POWDER"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["QUICK_POWDER"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.SPD, spdValue);
 
     expect(spdValue.value / spdStat).toBe(2);
@@ -167,7 +167,7 @@ describe("Items - Quick Powder", () => {
     expect(spdValue.value / spdStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["QUICK_POWDER"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["QUICK_POWDER"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.SPD, spdValue);
 
     expect(spdValue.value / spdStat).toBe(1);
diff --git a/src/test/items/scope_lens.test.ts b/src/test/items/scope_lens.test.ts
index 72dc838548e..60f7aec171b 100644
--- a/src/test/items/scope_lens.test.ts
+++ b/src/test/items/scope_lens.test.ts
@@ -55,7 +55,7 @@ describe("Items - Scope Lens", () => {
       Species.GASTLY
     ]);
 
-    const partyMember = game.scene.getPlayerPokemon();
+    const partyMember = game.scene.getPlayerPokemon()!;
 
     // Making sure modifier is not applied without holding item
     const critLevel = new Utils.IntegerHolder(0);
diff --git a/src/test/items/thick_club.test.ts b/src/test/items/thick_club.test.ts
index 6b56cf98099..841cd7c90ac 100644
--- a/src/test/items/thick_club.test.ts
+++ b/src/test/items/thick_club.test.ts
@@ -79,7 +79,7 @@ describe("Items - Thick Club", () => {
     expect(atkValue.value / atkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["THICK_CLUB"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["THICK_CLUB"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
 
     expect(atkValue.value / atkStat).toBe(2);
@@ -101,7 +101,7 @@ describe("Items - Thick Club", () => {
     expect(atkValue.value / atkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["THICK_CLUB"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["THICK_CLUB"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
 
     expect(atkValue.value / atkStat).toBe(2);
@@ -123,7 +123,7 @@ describe("Items - Thick Club", () => {
     expect(atkValue.value / atkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["THICK_CLUB"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["THICK_CLUB"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
 
     expect(atkValue.value / atkStat).toBe(2);
@@ -160,7 +160,7 @@ describe("Items - Thick Club", () => {
     expect(atkValue.value / atkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["THICK_CLUB"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["THICK_CLUB"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
 
     expect(atkValue.value / atkStat).toBe(2);
@@ -197,7 +197,7 @@ describe("Items - Thick Club", () => {
     expect(atkValue.value / atkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["THICK_CLUB"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["THICK_CLUB"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
 
     expect(atkValue.value / atkStat).toBe(2);
@@ -219,7 +219,7 @@ describe("Items - Thick Club", () => {
     expect(atkValue.value / atkStat).toBe(1);
 
     // Giving Eviolite to party member and testing if it applies
-    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType(null, ["THICK_CLUB"]).newModifier(partyMember), true);
+    partyMember.scene.addModifier(modifierTypes.SPECIES_STAT_BOOSTER().generateType([], ["THICK_CLUB"])!.newModifier(partyMember), true);
     partyMember.scene.applyModifiers(SpeciesStatBoosterModifier, true, partyMember, Stat.ATK, atkValue);
 
     expect(atkValue.value / atkStat).toBe(1);
diff --git a/src/test/items/toxic_orb.test.ts b/src/test/items/toxic_orb.test.ts
index b5e9b6c4d65..69f55cb2bbc 100644
--- a/src/test/items/toxic_orb.test.ts
+++ b/src/test/items/toxic_orb.test.ts
@@ -72,6 +72,6 @@ describe("Items - Toxic orb", () => {
     const message2 = game.textInterceptor.getLatestMessage();
     expect(message2).toContain("is hurt");
     expect(message2).toContain("by poison");
-    expect(game.scene.getParty()[0].status.effect).toBe(StatusEffect.TOXIC);
+    expect(game.scene.getParty()[0].status!.effect).toBe(StatusEffect.TOXIC);
   }, 20000);
 });
diff --git a/src/test/localization/terrain.test.ts b/src/test/localization/terrain.test.ts
index f97b7813948..c072f9cc9ab 100644
--- a/src/test/localization/terrain.test.ts
+++ b/src/test/localization/terrain.test.ts
@@ -37,18 +37,18 @@ describe("terrain", () => {
       mockI18next();
 
       const text = getTerrainStartMessage(terrainType);
-      expect(text).toBe(undefined);
+      expect(text).toBeNull();
     });
 
     it("should return the clear text", () => {
       mockI18next();
       const text = getTerrainClearMessage(terrainType);
-      expect(text).toBe(undefined);
+      expect(text).toBeNull();
     });
 
     it("should return the block text", async () => {
       await game.startBattle([Species.MAGIKARP]);
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       mockI18next();
       const text = getTerrainBlockMessage(pokemon, terrainType);
       expect(text).toBe("terrain:defaultBlockMessage");
@@ -80,7 +80,7 @@ describe("terrain", () => {
 
     it("should return the block text", async () => {
       await game.startBattle([Species.MAGIKARP]);
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       mockI18next();
       const text = getTerrainBlockMessage(pokemon, terrainType);
       expect(text).toBe("terrain:mistyBlockMessage");
@@ -112,7 +112,7 @@ describe("terrain", () => {
 
     it("should return the block text", async () => {
       await game.startBattle([Species.MAGIKARP]);
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       mockI18next();
       const text = getTerrainBlockMessage(pokemon, terrainType);
       expect(text).toBe("terrain:defaultBlockMessage");
@@ -144,7 +144,7 @@ describe("terrain", () => {
 
     it("should return the block text", async () => {
       await game.startBattle([Species.MAGIKARP]);
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       mockI18next();
       const text = getTerrainBlockMessage(pokemon, terrainType);
       expect(text).toBe("terrain:defaultBlockMessage");
@@ -176,7 +176,7 @@ describe("terrain", () => {
 
     it("should return the block text", async () => {
       await game.startBattle([Species.MAGIKARP]);
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       mockI18next();
       const text = getTerrainBlockMessage(pokemon, terrainType);
       expect(text).toBe("terrain:defaultBlockMessage");
diff --git a/src/test/moves/astonish.test.ts b/src/test/moves/astonish.test.ts
index c5d59f82102..358e4a9bec3 100644
--- a/src/test/moves/astonish.test.ts
+++ b/src/test/moves/astonish.test.ts
@@ -43,9 +43,9 @@ describe("Moves - Astonish", () => {
     async () => {
       await game.startBattle([Species.MEOWSCARADA]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.ASTONISH));
 
diff --git a/src/test/moves/aurora_veil.test.ts b/src/test/moves/aurora_veil.test.ts
index f98e9e9cc0c..a10c9b6b60a 100644
--- a/src/test/moves/aurora_veil.test.ts
+++ b/src/test/moves/aurora_veil.test.ts
@@ -49,7 +49,7 @@ describe("Moves - Aurora Veil", () => {
     game.doAttack(getMovePosition(game.scene, 0, moveToUse));
 
     await game.phaseInterceptor.to(TurnEndPhase);
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power * singleBattleMultiplier);
   });
@@ -64,7 +64,7 @@ describe("Moves - Aurora Veil", () => {
     game.doAttack(getMovePosition(game.scene, 1, moveToUse));
 
     await game.phaseInterceptor.to(TurnEndPhase);
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power * doubleBattleMultiplier);
   });
@@ -77,7 +77,7 @@ describe("Moves - Aurora Veil", () => {
 
     await game.phaseInterceptor.to(TurnEndPhase);
 
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power * singleBattleMultiplier);
   });
@@ -92,7 +92,7 @@ describe("Moves - Aurora Veil", () => {
     game.doAttack(getMovePosition(game.scene, 1, moveToUse));
 
     await game.phaseInterceptor.to(TurnEndPhase);
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power * doubleBattleMultiplier);
   });
diff --git a/src/test/moves/baton_pass.test.ts b/src/test/moves/baton_pass.test.ts
index ba961613998..9f0cb3619b2 100644
--- a/src/test/moves/baton_pass.test.ts
+++ b/src/test/moves/baton_pass.test.ts
@@ -45,7 +45,7 @@ describe("Moves - Baton Pass", () => {
     // round 1 - buff
     game.doAttack(getMovePosition(game.scene, 0, Moves.NASTY_PLOT));
     await game.toNextTurn();
-    expect(game.scene.getPlayerPokemon().summonData.battleStats[BattleStat.SPATK]).toEqual(2);
+    expect(game.scene.getPlayerPokemon()!.summonData.battleStats[BattleStat.SPATK]).toEqual(2);
 
     // round 2 - baton pass
     game.doAttack(getMovePosition(game.scene, 0, Moves.BATON_PASS));
@@ -53,8 +53,9 @@ describe("Moves - Baton Pass", () => {
     await game.phaseInterceptor.to(TurnEndPhase);
 
     // assert
-    expect(game.scene.getPlayerPokemon().species.speciesId).toEqual(Species.SHUCKLE);
-    expect(game.scene.getPlayerPokemon().summonData.battleStats[BattleStat.SPATK]).toEqual(2);
+    const playerPkm = game.scene.getPlayerPokemon()!;
+    expect(playerPkm.species.speciesId).toEqual(Species.SHUCKLE);
+    expect(playerPkm.summonData.battleStats[BattleStat.SPATK]).toEqual(2);
   }, 20000);
 
   it("passes stat stage buffs when AI uses it", async() => {
@@ -72,17 +73,17 @@ describe("Moves - Baton Pass", () => {
     await game.toNextTurn();
 
     // round 2 - baton pass
-    game.scene.getEnemyPokemon().hp = 100;
+    game.scene.getEnemyPokemon()!.hp = 100;
     game.override.enemyMoveset(new Array(4).fill(Moves.BATON_PASS));
     game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
     await game.phaseInterceptor.to(PostSummonPhase, false);
 
     // assert
     // check buffs are still there
-    expect(game.scene.getEnemyPokemon().summonData.battleStats[BattleStat.SPATK]).toEqual(2);
+    expect(game.scene.getEnemyPokemon()!.summonData.battleStats[BattleStat.SPATK]).toEqual(2);
     // confirm that a switch actually happened. can't use species because I
     // can't find a way to override trainer parties with more than 1 pokemon species
-    expect(game.scene.getEnemyPokemon().hp).not.toEqual(100);
+    expect(game.scene.getEnemyPokemon()!.hp).not.toEqual(100);
     expect(game.phaseInterceptor.log.slice(-4)).toEqual([
       "MoveEffectPhase",
       "SwitchSummonPhase",
diff --git a/src/test/moves/beat_up.test.ts b/src/test/moves/beat_up.test.ts
index e720c625956..a5e4b3cbd34 100644
--- a/src/test/moves/beat_up.test.ts
+++ b/src/test/moves/beat_up.test.ts
@@ -42,8 +42,8 @@ describe("Moves - Beat Up", () => {
     async () => {
       await game.startBattle([Species.MAGIKARP, Species.BULBASAUR, Species.CHARMANDER, Species.SQUIRTLE, Species.PIKACHU, Species.EEVEE]);
 
-      const playerPokemon = game.scene.getPlayerPokemon();
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       let enemyStartingHp = enemyPokemon.hp;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.BEAT_UP));
@@ -66,7 +66,7 @@ describe("Moves - Beat Up", () => {
     async () => {
       await game.startBattle([Species.MAGIKARP, Species.BULBASAUR, Species.CHARMANDER, Species.SQUIRTLE, Species.PIKACHU, Species.EEVEE]);
 
-      const playerPokemon = game.scene.getPlayerPokemon();
+      const playerPokemon = game.scene.getPlayerPokemon()!;
 
       game.scene.getParty()[1].trySetStatus(StatusEffect.BURN);
 
@@ -84,8 +84,8 @@ describe("Moves - Beat Up", () => {
       game.override.startingHeldItems([{name: "MULTI_LENS", count: 1}]);
       await game.startBattle([Species.MAGIKARP, Species.BULBASAUR, Species.CHARMANDER, Species.SQUIRTLE, Species.PIKACHU, Species.EEVEE]);
 
-      const playerPokemon = game.scene.getPlayerPokemon();
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
       let enemyStartingHp = enemyPokemon.hp;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.BEAT_UP));
diff --git a/src/test/moves/belly_drum.test.ts b/src/test/moves/belly_drum.test.ts
index 5bb27394805..74afc910faf 100644
--- a/src/test/moves/belly_drum.test.ts
+++ b/src/test/moves/belly_drum.test.ts
@@ -43,7 +43,7 @@ describe("Moves - BELLY DRUM", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       const hpLost = Math.floor(leadPokemon.getMaxHp() / RATIO);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.BELLY_DRUM));
@@ -58,7 +58,7 @@ describe("Moves - BELLY DRUM", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       const hpLost = Math.floor(leadPokemon.getMaxHp() / RATIO);
 
       // Here - BattleStat.ATK -> -3 and BattleStat.SPATK -> 6
@@ -78,7 +78,7 @@ describe("Moves - BELLY DRUM", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
 
       leadPokemon.summonData.battleStats[BattleStat.ATK] = 6;
 
@@ -94,7 +94,7 @@ describe("Moves - BELLY DRUM", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       const hpLost = Math.floor(leadPokemon.getMaxHp() / RATIO);
       leadPokemon.hp = hpLost - PREDAMAGE;
 
diff --git a/src/test/moves/ceaseless_edge.test.ts b/src/test/moves/ceaseless_edge.test.ts
index 288ea6ac277..c5ce8375102 100644
--- a/src/test/moves/ceaseless_edge.test.ts
+++ b/src/test/moves/ceaseless_edge.test.ts
@@ -45,7 +45,7 @@ describe("Moves - Ceaseless Edge", () => {
     async () => {
       await game.startBattle([ Species.ILLUMISE ]);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       const enemyStartingHp = enemyPokemon.hp;
 
@@ -70,7 +70,7 @@ describe("Moves - Ceaseless Edge", () => {
       game.override.startingHeldItems([{name: "MULTI_LENS"}]);
       await game.startBattle([ Species.ILLUMISE ]);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       const enemyStartingHp = enemyPokemon.hp;
 
diff --git a/src/test/moves/clangorous_soul.test.ts b/src/test/moves/clangorous_soul.test.ts
index 251225e7068..5493466ba56 100644
--- a/src/test/moves/clangorous_soul.test.ts
+++ b/src/test/moves/clangorous_soul.test.ts
@@ -44,7 +44,7 @@ describe("Moves - CLANGOROUS_SOUL", () => {
   	async() => {
   	 	await game.startBattle([Species.MAGIKARP]);
 
-     	const leadPokemon = game.scene.getPlayerPokemon();
+     	const leadPokemon = game.scene.getPlayerPokemon()!;
       const hpLost = Math.floor(leadPokemon.getMaxHp() / RATIO);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.CLANGOROUS_SOUL));
@@ -63,7 +63,7 @@ describe("Moves - CLANGOROUS_SOUL", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       const hpLost = Math.floor(leadPokemon.getMaxHp() / RATIO);
 
       //Here - BattleStat.SPD -> 0 and BattleStat.SPDEF -> 4
@@ -88,7 +88,7 @@ describe("Moves - CLANGOROUS_SOUL", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
 
       leadPokemon.summonData.battleStats[BattleStat.ATK] = 6;
       leadPokemon.summonData.battleStats[BattleStat.DEF] = 6;
@@ -112,7 +112,7 @@ describe("Moves - CLANGOROUS_SOUL", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       const hpLost = Math.floor(leadPokemon.getMaxHp() / RATIO);
       leadPokemon.hp = hpLost - PREDAMAGE;
 
diff --git a/src/test/moves/double_team.test.ts b/src/test/moves/double_team.test.ts
index 48b322f5f11..2153b856517 100644
--- a/src/test/moves/double_team.test.ts
+++ b/src/test/moves/double_team.test.ts
@@ -36,8 +36,8 @@ describe("Moves - Double Team", () => {
   it("increases the user's evasion by one stage.", async () => {
     await game.startBattle([Species.MAGIKARP]);
 
-    const ally = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const ally = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(enemy, "getAccuracyMultiplier");
     expect(ally.summonData.battleStats[BattleStat.EVA]).toBe(0);
diff --git a/src/test/moves/dragon_rage.test.ts b/src/test/moves/dragon_rage.test.ts
index 3c6e2b83baa..6ec7521f678 100644
--- a/src/test/moves/dragon_rage.test.ts
+++ b/src/test/moves/dragon_rage.test.ts
@@ -51,7 +51,7 @@ describe("Moves - Dragon Rage", () => {
     await game.startBattle();
 
     partyPokemon = game.scene.getParty()[0];
-    enemyPokemon = game.scene.getEnemyPokemon();
+    enemyPokemon = game.scene.getEnemyPokemon()!;
 
     // remove berries
     game.scene.removePartyMemberModifiers(0);
diff --git a/src/test/moves/dynamax_cannon.test.ts b/src/test/moves/dynamax_cannon.test.ts
index 8af6a624797..57846c1aef7 100644
--- a/src/test/moves/dynamax_cannon.test.ts
+++ b/src/test/moves/dynamax_cannon.test.ts
@@ -81,7 +81,7 @@ describe("Moves - Dynamax Cannon", () => {
     const phase = game.scene.getCurrentPhase() as MoveEffectPhase;
     expect(phase.move.moveId).toBe(dynamaxCannon.id);
     // Force level cap to be 100
-    vi.spyOn(phase.getTarget().scene, "getMaxExpLevel").mockReturnValue(100);
+    vi.spyOn(phase.getTarget()!.scene, "getMaxExpLevel").mockReturnValue(100);
     await game.phaseInterceptor.to(DamagePhase, false);
     expect(dynamaxCannon.calculateBattlePower).toHaveLastReturnedWith(120);
   }, 20000);
@@ -98,7 +98,7 @@ describe("Moves - Dynamax Cannon", () => {
     const phase = game.scene.getCurrentPhase() as MoveEffectPhase;
     expect(phase.move.moveId).toBe(dynamaxCannon.id);
     // Force level cap to be 100
-    vi.spyOn(phase.getTarget().scene, "getMaxExpLevel").mockReturnValue(100);
+    vi.spyOn(phase.getTarget()!.scene, "getMaxExpLevel").mockReturnValue(100);
     await game.phaseInterceptor.to(DamagePhase, false);
     expect(dynamaxCannon.calculateBattlePower).toHaveLastReturnedWith(140);
   }, 20000);
@@ -115,7 +115,7 @@ describe("Moves - Dynamax Cannon", () => {
     const phase = game.scene.getCurrentPhase() as MoveEffectPhase;
     expect(phase.move.moveId).toBe(dynamaxCannon.id);
     // Force level cap to be 100
-    vi.spyOn(phase.getTarget().scene, "getMaxExpLevel").mockReturnValue(100);
+    vi.spyOn(phase.getTarget()!.scene, "getMaxExpLevel").mockReturnValue(100);
     await game.phaseInterceptor.to(DamagePhase, false);
     expect(dynamaxCannon.calculateBattlePower).toHaveLastReturnedWith(160);
   }, 20000);
@@ -132,7 +132,7 @@ describe("Moves - Dynamax Cannon", () => {
     const phase = game.scene.getCurrentPhase() as MoveEffectPhase;
     expect(phase.move.moveId).toBe(dynamaxCannon.id);
     // Force level cap to be 100
-    vi.spyOn(phase.getTarget().scene, "getMaxExpLevel").mockReturnValue(100);
+    vi.spyOn(phase.getTarget()!.scene, "getMaxExpLevel").mockReturnValue(100);
     await game.phaseInterceptor.to(DamagePhase, false);
     expect(dynamaxCannon.calculateBattlePower).toHaveLastReturnedWith(180);
   }, 20000);
@@ -149,7 +149,7 @@ describe("Moves - Dynamax Cannon", () => {
     const phase = game.scene.getCurrentPhase() as MoveEffectPhase;
     expect(phase.move.moveId).toBe(dynamaxCannon.id);
     // Force level cap to be 100
-    vi.spyOn(phase.getTarget().scene, "getMaxExpLevel").mockReturnValue(100);
+    vi.spyOn(phase.getTarget()!.scene, "getMaxExpLevel").mockReturnValue(100);
     await game.phaseInterceptor.to(DamagePhase, false);
     expect(dynamaxCannon.calculateBattlePower).toHaveLastReturnedWith(200);
   }, 20000);
diff --git a/src/test/moves/fillet_away.test.ts b/src/test/moves/fillet_away.test.ts
index a3922b18468..6965ced46d9 100644
--- a/src/test/moves/fillet_away.test.ts
+++ b/src/test/moves/fillet_away.test.ts
@@ -44,7 +44,7 @@ describe("Moves - FILLET AWAY", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       const hpLost = Math.floor(leadPokemon.getMaxHp() / RATIO);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.FILLET_AWAY));
@@ -61,7 +61,7 @@ describe("Moves - FILLET AWAY", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       const hpLost = Math.floor(leadPokemon.getMaxHp() / RATIO);
 
       //Here - BattleStat.SPD -> 0 and BattleStat.SPATK -> 3
@@ -82,7 +82,7 @@ describe("Moves - FILLET AWAY", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
 
       leadPokemon.summonData.battleStats[BattleStat.ATK] = 6;
       leadPokemon.summonData.battleStats[BattleStat.SPATK] = 6;
@@ -102,7 +102,7 @@ describe("Moves - FILLET AWAY", () => {
     async() => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
       const hpLost = Math.floor(leadPokemon.getMaxHp() / RATIO);
       leadPokemon.hp = hpLost - PREDAMAGE;
 
diff --git a/src/test/moves/fissure.test.ts b/src/test/moves/fissure.test.ts
index f2f58212209..979bc40646c 100644
--- a/src/test/moves/fissure.test.ts
+++ b/src/test/moves/fissure.test.ts
@@ -45,7 +45,7 @@ describe("Moves - Fissure", () => {
     await game.startBattle();
 
     partyPokemon = game.scene.getParty()[0];
-    enemyPokemon = game.scene.getEnemyPokemon();
+    enemyPokemon = game.scene.getEnemyPokemon()!;
 
     // remove berries
     game.scene.removePartyMemberModifiers(0);
diff --git a/src/test/moves/flower_shield.test.ts b/src/test/moves/flower_shield.test.ts
index a00c84f8714..7ca5fb8bc62 100644
--- a/src/test/moves/flower_shield.test.ts
+++ b/src/test/moves/flower_shield.test.ts
@@ -39,8 +39,8 @@ describe("Moves - Flower Shield", () => {
     game.override.enemySpecies(Species.CHERRIM);
 
     await game.startBattle([Species.MAGIKARP]);
-    const cherrim = game.scene.getEnemyPokemon();
-    const magikarp = game.scene.getPlayerPokemon();
+    const cherrim = game.scene.getEnemyPokemon()!;
+    const magikarp = game.scene.getPlayerPokemon()!;
 
     expect(magikarp.summonData.battleStats[BattleStat.DEF]).toBe(0);
     expect(cherrim.summonData.battleStats[BattleStat.DEF]).toBe(0);
@@ -81,8 +81,8 @@ describe("Moves - Flower Shield", () => {
     game.override.enemyLevel(50);
 
     await game.startBattle([Species.CHERRIM]);
-    const paras = game.scene.getEnemyPokemon();
-    const cherrim = game.scene.getPlayerPokemon();
+    const paras = game.scene.getEnemyPokemon()!;
+    const cherrim = game.scene.getPlayerPokemon()!;
 
     expect(paras.summonData.battleStats[BattleStat.DEF]).toBe(0);
     expect(cherrim.summonData.battleStats[BattleStat.DEF]).toBe(0);
@@ -100,8 +100,8 @@ describe("Moves - Flower Shield", () => {
     game.override.enemySpecies(Species.MAGIKARP);
 
     await game.startBattle([Species.MAGIKARP]);
-    const enemy = game.scene.getEnemyPokemon();
-    const ally = game.scene.getPlayerPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
+    const ally = game.scene.getPlayerPokemon()!;
 
     expect(enemy.summonData.battleStats[BattleStat.DEF]).toBe(0);
     expect(ally.summonData.battleStats[BattleStat.DEF]).toBe(0);
diff --git a/src/test/moves/foresight.test.ts b/src/test/moves/foresight.test.ts
index 4a2b4f8af03..5d847ca1bc4 100644
--- a/src/test/moves/foresight.test.ts
+++ b/src/test/moves/foresight.test.ts
@@ -35,7 +35,7 @@ describe("Internals", () => {
   it("should allow Normal and Fighting moves to hit Ghost types", async () => {
     await game.startBattle();
 
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.QUICK_ATTACK));
     await game.toNextTurn();
@@ -59,7 +59,7 @@ describe("Internals", () => {
     game.override.enemyMoveset(Array(4).fill(Moves.MINIMIZE));
     await game.startBattle();
 
-    const pokemon = game.scene.getPlayerPokemon();
+    const pokemon = game.scene.getPlayerPokemon()!;
     vi.spyOn(pokemon, "getAccuracyMultiplier");
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.FORESIGHT));
diff --git a/src/test/moves/fusion_bolt.test.ts b/src/test/moves/fusion_bolt.test.ts
index 3ba4148db9f..c7a21e2c736 100644
--- a/src/test/moves/fusion_bolt.test.ts
+++ b/src/test/moves/fusion_bolt.test.ts
@@ -41,7 +41,7 @@ describe("Moves - Fusion Bolt", () => {
       Species.ZEKROM,
     ]);
 
-    const partyMember = game.scene.getPlayerPokemon();
+    const partyMember = game.scene.getPlayerPokemon()!;
     const initialHp = partyMember.hp;
 
     game.doAttack(getMovePosition(game.scene, 0, fusionBolt));
diff --git a/src/test/moves/fusion_flare.test.ts b/src/test/moves/fusion_flare.test.ts
index 9862995be32..9ae42e7977f 100644
--- a/src/test/moves/fusion_flare.test.ts
+++ b/src/test/moves/fusion_flare.test.ts
@@ -41,7 +41,7 @@ describe("Moves - Fusion Flare", () => {
       Species.RESHIRAM,
     ]);
 
-    const partyMember = game.scene.getPlayerPokemon();
+    const partyMember = game.scene.getPlayerPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, fusionFlare));
 
@@ -49,7 +49,7 @@ describe("Moves - Fusion Flare", () => {
 
     // Inflict freeze quietly and check if it was properly inflicted
     partyMember.trySetStatus(StatusEffect.FREEZE, false);
-    expect(partyMember.status.effect).toBe(StatusEffect.FREEZE);
+    expect(partyMember.status!.effect).toBe(StatusEffect.FREEZE);
 
     await game.toNextTurn();
 
diff --git a/src/test/moves/gastro_acid.test.ts b/src/test/moves/gastro_acid.test.ts
index c6692d3442c..77cf35f39e2 100644
--- a/src/test/moves/gastro_acid.test.ts
+++ b/src/test/moves/gastro_acid.test.ts
@@ -83,6 +83,6 @@ describe("Moves - Gastro Acid", () => {
 
     await game.phaseInterceptor.to("TurnInitPhase");
 
-    expect(game.scene.getPlayerPokemon().getLastXMoves()[0].result).toBe(MoveResult.FAIL);
+    expect(game.scene.getPlayerPokemon()!.getLastXMoves()[0].result).toBe(MoveResult.FAIL);
   }, TIMEOUT);
 });
diff --git a/src/test/moves/glaive_rush.test.ts b/src/test/moves/glaive_rush.test.ts
index fc9f6ee1c7f..ce63da6b565 100644
--- a/src/test/moves/glaive_rush.test.ts
+++ b/src/test/moves/glaive_rush.test.ts
@@ -38,7 +38,7 @@ describe("Moves - Glaive Rush", () => {
 
   it("takes double damage from attacks", async() => {
     await game.startBattle();
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
     enemy.hp = 1000;
 
     vi.spyOn(game.scene, "randBattleSeedInt").mockReturnValue(0);
@@ -50,11 +50,11 @@ describe("Moves - Glaive Rush", () => {
     await game.phaseInterceptor.to(DamagePhase);
     expect(enemy.hp).toBeLessThanOrEqual(1001 - (damageDealt * 3));
 
-  }, 20000);
+  }, 5000); // TODO: revert back to 20s
 
   it("always gets hit by attacks", async() => {
     await game.startBattle();
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
     enemy.hp = 1000;
 
     allMoves[Moves.AVALANCHE].accuracy = 0;
@@ -68,8 +68,8 @@ describe("Moves - Glaive Rush", () => {
     game.override.startingHeldItems([{name: "MULTI_LENS", count: 2}]);
     game.override.enemyMoveset(Array(4).fill(Moves.AVALANCHE));
     await game.startBattle();
-    const player = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const player = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
     enemy.hp = 1000;
     player.hp = 1000;
 
@@ -87,8 +87,8 @@ describe("Moves - Glaive Rush", () => {
   it("secondary effects only last until next move", async() => {
     game.override.enemyMoveset(Array(4).fill(Moves.SHADOW_SNEAK));
     await game.startBattle();
-    const player = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const player = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
     enemy.hp = 1000;
     player.hp = 1000;
     allMoves[Moves.SHADOW_SNEAK].accuracy = 0;
@@ -112,8 +112,8 @@ describe("Moves - Glaive Rush", () => {
     game.override.enemyMoveset(Array(4).fill(Moves.SHADOW_SNEAK));
     game.override.starterSpecies(0);
     await game.startBattle([Species.KLINK, Species.FEEBAS]);
-    const player = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const player = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
     enemy.hp = 1000;
     allMoves[Moves.SHADOW_SNEAK].accuracy = 0;
 
diff --git a/src/test/moves/hard_press.test.ts b/src/test/moves/hard_press.test.ts
index 6a45e49137b..baf63a1ad23 100644
--- a/src/test/moves/hard_press.test.ts
+++ b/src/test/moves/hard_press.test.ts
@@ -48,7 +48,7 @@ describe("Moves - Hard Press", () => {
   it("should return 50 power if target HP ratio is at 50%", async () => {
     await game.startBattle([Species.PIKACHU]);
     const targetHpRatio = .5;
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(enemy, "getHpRatio").mockReturnValue(targetHpRatio);
 
@@ -61,7 +61,7 @@ describe("Moves - Hard Press", () => {
   it("should return 1 power if target HP ratio is at 1%", async () => {
     await game.startBattle([Species.PIKACHU]);
     const targetHpRatio = .01;
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(enemy, "getHpRatio").mockReturnValue(targetHpRatio);
 
@@ -74,7 +74,7 @@ describe("Moves - Hard Press", () => {
   it("should return 1 power if target HP ratio is less than 1%", async () => {
     await game.startBattle([Species.PIKACHU]);
     const targetHpRatio = .005;
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
 
     vi.spyOn(enemy, "getHpRatio").mockReturnValue(targetHpRatio);
 
diff --git a/src/test/moves/hyper_beam.test.ts b/src/test/moves/hyper_beam.test.ts
index e7d3454ba32..369d4cac853 100644
--- a/src/test/moves/hyper_beam.test.ts
+++ b/src/test/moves/hyper_beam.test.ts
@@ -43,8 +43,8 @@ describe("Moves - Hyper Beam", () => {
     async () => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const leadPokemon = game.scene.getPlayerPokemon();
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const leadPokemon = game.scene.getPlayerPokemon()!;
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.HYPER_BEAM));
 
diff --git a/src/test/moves/light_screen.test.ts b/src/test/moves/light_screen.test.ts
index e47b6fe93ea..9de1f8c492b 100644
--- a/src/test/moves/light_screen.test.ts
+++ b/src/test/moves/light_screen.test.ts
@@ -48,7 +48,7 @@ describe("Moves - Light Screen", () => {
 
     await game.phaseInterceptor.to(TurnEndPhase);
 
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power * singleBattleMultiplier);
   });
@@ -63,7 +63,7 @@ describe("Moves - Light Screen", () => {
     game.doAttack(getMovePosition(game.scene, 1, moveToUse));
 
     await game.phaseInterceptor.to(TurnEndPhase);
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power * doubleBattleMultiplier);
   });
@@ -75,7 +75,7 @@ describe("Moves - Light Screen", () => {
     game.doAttack(getMovePosition(game.scene, 0, moveToUse));
 
     await game.phaseInterceptor.to(TurnEndPhase);
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power);
   });
diff --git a/src/test/moves/lucky_chant.test.ts b/src/test/moves/lucky_chant.test.ts
index 1a29edb8052..1232ce9ffc3 100644
--- a/src/test/moves/lucky_chant.test.ts
+++ b/src/test/moves/lucky_chant.test.ts
@@ -41,7 +41,7 @@ describe("Moves - Lucky Chant", () => {
     async () => {
       await game.startBattle([Species.CHARIZARD]);
 
-      const playerPokemon = game.scene.getPlayerPokemon();
+      const playerPokemon = game.scene.getPlayerPokemon()!;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
 
@@ -91,8 +91,8 @@ describe("Moves - Lucky Chant", () => {
 
       await game.startBattle([Species.CHARIZARD]);
 
-      const playerPokemon = game.scene.getPlayerPokemon();
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       enemyPokemon.addTag(BattlerTagType.ALWAYS_CRIT, 2, Moves.NONE, 0);
 
diff --git a/src/test/moves/make_it_rain.test.ts b/src/test/moves/make_it_rain.test.ts
index 850f8f644b8..72386930873 100644
--- a/src/test/moves/make_it_rain.test.ts
+++ b/src/test/moves/make_it_rain.test.ts
@@ -55,8 +55,8 @@ describe("Moves - Make It Rain", () => {
 
     await game.startBattle([Species.CHARIZARD]);
 
-    const playerPokemon = game.scene.getPlayerPokemon();
-    const enemyPokemon = game.scene.getEnemyPokemon();
+    const playerPokemon = game.scene.getPlayerPokemon()!;
+    const enemyPokemon = game.scene.getEnemyPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.MAKE_IT_RAIN));
 
diff --git a/src/test/moves/miracle_eye.test.ts b/src/test/moves/miracle_eye.test.ts
index 188c5736fc4..53d575ea96d 100644
--- a/src/test/moves/miracle_eye.test.ts
+++ b/src/test/moves/miracle_eye.test.ts
@@ -35,7 +35,7 @@ describe("Internals", () => {
   it("should allow Psychic moves to hit Dark types", async () => {
     await game.startBattle();
 
-    const enemy = game.scene.getEnemyPokemon();
+    const enemy = game.scene.getEnemyPokemon()!;
 
     game.doAttack(getMovePosition(game.scene, 0, Moves.CONFUSION));
     await game.toNextTurn();
diff --git a/src/test/moves/purify.test.ts b/src/test/moves/purify.test.ts
index 4d108c43d4b..0367cc5a9b2 100644
--- a/src/test/moves/purify.test.ts
+++ b/src/test/moves/purify.test.ts
@@ -42,8 +42,8 @@ describe("Moves - Purify", () => {
     async () => {
       await game.startBattle();
 
-      const enemyPokemon: EnemyPokemon = game.scene.getEnemyPokemon();
-      const playerPokemon: PlayerPokemon = game.scene.getPlayerPokemon();
+      const enemyPokemon: EnemyPokemon = game.scene.getEnemyPokemon()!;
+      const playerPokemon: PlayerPokemon = game.scene.getPlayerPokemon()!;
 
       playerPokemon.hp = playerPokemon.getMaxHp() - 1;
       enemyPokemon.status = new Status(StatusEffect.BURN);
@@ -51,7 +51,7 @@ describe("Moves - Purify", () => {
       game.doAttack(getMovePosition(game.scene, 0, Moves.PURIFY));
       await game.phaseInterceptor.to(MoveEndPhase);
 
-      expect(enemyPokemon.status).toBe(undefined);
+      expect(enemyPokemon.status).toBeNull();
       expect(playerPokemon.isFullHp()).toBe(true);
     },
     TIMEOUT
@@ -62,7 +62,7 @@ describe("Moves - Purify", () => {
     async () => {
       await game.startBattle();
 
-      const playerPokemon: PlayerPokemon = game.scene.getPlayerPokemon();
+      const playerPokemon: PlayerPokemon = game.scene.getPlayerPokemon()!;
 
       playerPokemon.hp = playerPokemon.getMaxHp() - 1;
       const playerInitialHp = playerPokemon.hp;
diff --git a/src/test/moves/reflect.test.ts b/src/test/moves/reflect.test.ts
index 821d9df437a..f5ea489a75e 100644
--- a/src/test/moves/reflect.test.ts
+++ b/src/test/moves/reflect.test.ts
@@ -47,7 +47,7 @@ describe("Moves - Reflect", () => {
     game.doAttack(getMovePosition(game.scene, 0, moveToUse));
 
     await game.phaseInterceptor.to(TurnEndPhase);
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power * singleBattleMultiplier);
   });
@@ -62,7 +62,7 @@ describe("Moves - Reflect", () => {
     game.doAttack(getMovePosition(game.scene, 1, moveToUse));
 
     await game.phaseInterceptor.to(TurnEndPhase);
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power * doubleBattleMultiplier);
   });
@@ -75,7 +75,7 @@ describe("Moves - Reflect", () => {
 
     await game.phaseInterceptor.to(TurnEndPhase);
 
-    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon(), game.scene.getPlayerPokemon(), allMoves[moveToUse]);
+    const mockedDmg = getMockedMoveDamage(game.scene.getEnemyPokemon()!, game.scene.getPlayerPokemon()!, allMoves[moveToUse]);
 
     expect(mockedDmg).toBe(allMoves[moveToUse].power);
   });
diff --git a/src/test/moves/roost.test.ts b/src/test/moves/roost.test.ts
index 9ebd52e457d..a9036dcb478 100644
--- a/src/test/moves/roost.test.ts
+++ b/src/test/moves/roost.test.ts
@@ -40,7 +40,7 @@ describe("Moves - Roost", () => {
     async () => {
       await game.startBattle([Species.MAGIKARP]);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       const enemyStartingHp = enemyPokemon.hp;
 
diff --git a/src/test/moves/spit_up.test.ts b/src/test/moves/spit_up.test.ts
index 298c96d6d66..ec0a53028ff 100644
--- a/src/test/moves/spit_up.test.ts
+++ b/src/test/moves/spit_up.test.ts
@@ -45,10 +45,10 @@ describe("Moves - Spit Up", () => {
 
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
       expect(stockpilingTag.stockpiledCount).toBe(stacksToSetup);
 
@@ -69,11 +69,11 @@ describe("Moves - Spit Up", () => {
 
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       pokemon.addTag(BattlerTagType.STOCKPILING);
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
       expect(stockpilingTag.stockpiledCount).toBe(stacksToSetup);
 
@@ -94,12 +94,12 @@ describe("Moves - Spit Up", () => {
 
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       pokemon.addTag(BattlerTagType.STOCKPILING);
       pokemon.addTag(BattlerTagType.STOCKPILING);
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
       expect(stockpilingTag.stockpiledCount).toBe(stacksToSetup);
 
@@ -118,9 +118,9 @@ describe("Moves - Spit Up", () => {
   it("fails without stacks", { timeout: 10000 }, async () => {
     await game.startBattle([Species.ABOMASNOW]);
 
-    const pokemon = game.scene.getPlayerPokemon();
+    const pokemon = game.scene.getPlayerPokemon()!;
 
-    const stockpilingTag = pokemon.getTag(StockpilingTag);
+    const stockpilingTag = pokemon.getTag(StockpilingTag)!;
     expect(stockpilingTag).toBeUndefined();
 
     vi.spyOn(allMoves[Moves.SPIT_UP], "calculateBattlePower");
@@ -137,10 +137,10 @@ describe("Moves - Spit Up", () => {
     it("decreases stats based on stored values (both boosts equal)", { timeout: 10000 }, async () => {
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
 
       vi.spyOn(allMoves[Moves.SPIT_UP], "calculateBattlePower");
@@ -166,10 +166,10 @@ describe("Moves - Spit Up", () => {
     it("decreases stats based on stored values (different boosts)", { timeout: 10000 }, async () => {
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
 
       // for the sake of simplicity (and because other tests cover the setup), set boost amounts directly
diff --git a/src/test/moves/stockpile.test.ts b/src/test/moves/stockpile.test.ts
index 604b08745eb..375eeab3c95 100644
--- a/src/test/moves/stockpile.test.ts
+++ b/src/test/moves/stockpile.test.ts
@@ -41,7 +41,7 @@ describe("Moves - Stockpile", () => {
     it("Gains a stockpile stack and increases DEF and SPDEF by 1 on each use, fails at max stacks (3)", { timeout: 10000 }, async () => {
       await game.startBattle([Species.ABOMASNOW]);
 
-      const user = game.scene.getPlayerPokemon();
+      const user = game.scene.getPlayerPokemon()!;
 
       // Unfortunately, Stockpile stacks are not directly queryable (i.e. there is no pokemon.getStockpileStacks()),
       // we just have to know that they're implemented as a BattlerTag.
@@ -59,7 +59,7 @@ describe("Moves - Stockpile", () => {
         game.doAttack(getMovePosition(game.scene, 0, Moves.STOCKPILE));
         await game.phaseInterceptor.to(TurnInitPhase);
 
-        const stockpilingTag = user.getTag(StockpilingTag);
+        const stockpilingTag = user.getTag(StockpilingTag)!;
         const def = user.summonData.battleStats[BattleStat.DEF];
         const spdef = user.summonData.battleStats[BattleStat.SPDEF];
 
@@ -82,7 +82,7 @@ describe("Moves - Stockpile", () => {
     it("Gains a stockpile stack even if DEF and SPDEF are at +6", { timeout: 10000 }, async () => {
       await game.startBattle([Species.ABOMASNOW]);
 
-      const user = game.scene.getPlayerPokemon();
+      const user = game.scene.getPlayerPokemon()!;
 
       user.summonData.battleStats[BattleStat.DEF] = 6;
       user.summonData.battleStats[BattleStat.SPDEF] = 6;
@@ -94,7 +94,7 @@ describe("Moves - Stockpile", () => {
       game.doAttack(getMovePosition(game.scene, 0, Moves.STOCKPILE));
       await game.phaseInterceptor.to(TurnInitPhase);
 
-      const stockpilingTag = user.getTag(StockpilingTag);
+      const stockpilingTag = user.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
       expect(stockpilingTag.stockpiledCount).toBe(1);
       expect(user.summonData.battleStats[BattleStat.DEF]).toBe(6);
@@ -106,7 +106,7 @@ describe("Moves - Stockpile", () => {
       game.doAttack(getMovePosition(game.scene, 0, Moves.STOCKPILE));
       await game.phaseInterceptor.to(TurnInitPhase);
 
-      const stockpilingTagAgain = user.getTag(StockpilingTag);
+      const stockpilingTagAgain = user.getTag(StockpilingTag)!;
       expect(stockpilingTagAgain).toBeDefined();
       expect(stockpilingTagAgain.stockpiledCount).toBe(2);
       expect(user.summonData.battleStats[BattleStat.DEF]).toBe(6);
diff --git a/src/test/moves/swallow.test.ts b/src/test/moves/swallow.test.ts
index 9a0a19dce2b..aed30445fd2 100644
--- a/src/test/moves/swallow.test.ts
+++ b/src/test/moves/swallow.test.ts
@@ -44,13 +44,13 @@ describe("Moves - Swallow", () => {
 
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       vi.spyOn(pokemon, "getMaxHp").mockReturnValue(100);
       pokemon["hp"] = 1;
 
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
       expect(stockpilingTag.stockpiledCount).toBe(stacksToSetup);
 
@@ -71,14 +71,14 @@ describe("Moves - Swallow", () => {
 
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       vi.spyOn(pokemon, "getMaxHp").mockReturnValue(100);
       pokemon["hp"] = 1;
 
       pokemon.addTag(BattlerTagType.STOCKPILING);
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
       expect(stockpilingTag.stockpiledCount).toBe(stacksToSetup);
 
@@ -99,7 +99,7 @@ describe("Moves - Swallow", () => {
 
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       vi.spyOn(pokemon, "getMaxHp").mockReturnValue(100);
       pokemon["hp"] = 0.0001;
 
@@ -107,7 +107,7 @@ describe("Moves - Swallow", () => {
       pokemon.addTag(BattlerTagType.STOCKPILING);
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
       expect(stockpilingTag.stockpiledCount).toBe(stacksToSetup);
 
@@ -126,9 +126,9 @@ describe("Moves - Swallow", () => {
   it("fails without stacks", { timeout: 10000 }, async () => {
     await game.startBattle([Species.ABOMASNOW]);
 
-    const pokemon = game.scene.getPlayerPokemon();
+    const pokemon = game.scene.getPlayerPokemon()!;
 
-    const stockpilingTag = pokemon.getTag(StockpilingTag);
+    const stockpilingTag = pokemon.getTag(StockpilingTag)!;
     expect(stockpilingTag).toBeUndefined();
 
     game.doAttack(0);
@@ -141,10 +141,10 @@ describe("Moves - Swallow", () => {
     it("decreases stats based on stored values (both boosts equal)", { timeout: 10000 }, async () => {
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
 
       game.doAttack(0);
@@ -166,10 +166,10 @@ describe("Moves - Swallow", () => {
     it("decreases stats based on stored values (different boosts)", { timeout: 10000 }, async () => {
       await game.startBattle([Species.ABOMASNOW]);
 
-      const pokemon = game.scene.getPlayerPokemon();
+      const pokemon = game.scene.getPlayerPokemon()!;
       pokemon.addTag(BattlerTagType.STOCKPILING);
 
-      const stockpilingTag = pokemon.getTag(StockpilingTag);
+      const stockpilingTag = pokemon.getTag(StockpilingTag)!;
       expect(stockpilingTag).toBeDefined();
 
       // for the sake of simplicity (and because other tests cover the setup), set boost amounts directly
diff --git a/src/test/moves/tailwind.test.ts b/src/test/moves/tailwind.test.ts
index d88de680d8a..b2643dc68f3 100644
--- a/src/test/moves/tailwind.test.ts
+++ b/src/test/moves/tailwind.test.ts
@@ -80,8 +80,8 @@ describe("Abilities - Wind Rider", () => {
 
     await game.startBattle([Species.MAGIKARP]);
 
-    const ally = game.scene.getPlayerPokemon();
-    const enemy = game.scene.getEnemyPokemon();
+    const ally = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
 
     const allySpd = ally.getStat(Stat.SPD);
     const enemySpd = enemy.getStat(Stat.SPD);
diff --git a/src/test/moves/thousand_arrows.test.ts b/src/test/moves/thousand_arrows.test.ts
index 3b15610f896..84a71ee5256 100644
--- a/src/test/moves/thousand_arrows.test.ts
+++ b/src/test/moves/thousand_arrows.test.ts
@@ -39,7 +39,7 @@ describe("Moves - Thousand Arrows", () => {
     async () => {
       await game.startBattle([ Species.ILLUMISE ]);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.THOUSAND_ARROWS));
 
@@ -62,7 +62,7 @@ describe("Moves - Thousand Arrows", () => {
 
       await game.startBattle([ Species.ILLUMISE ]);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.THOUSAND_ARROWS));
 
@@ -84,9 +84,9 @@ describe("Moves - Thousand Arrows", () => {
 
       await game.startBattle([ Species.ILLUMISE ]);
 
-      const enemyPokemon = game.scene.getEnemyPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon()!;
 
-      enemyPokemon.addTag(BattlerTagType.MAGNET_RISEN, null, Moves.MAGNET_RISE);
+      enemyPokemon.addTag(BattlerTagType.MAGNET_RISEN, undefined, Moves.MAGNET_RISE);
 
       game.doAttack(getMovePosition(game.scene, 0, Moves.THOUSAND_ARROWS));
 
diff --git a/src/test/moves/tidy_up.test.ts b/src/test/moves/tidy_up.test.ts
index 83e1dda07cb..e35a438c562 100644
--- a/src/test/moves/tidy_up.test.ts
+++ b/src/test/moves/tidy_up.test.ts
@@ -106,7 +106,7 @@ describe("Moves - Tidy Up", () => {
 
   it("user's stats are raised with no traps set", async() => {
     await game.startBattle();
-    const player = game.scene.getPlayerPokemon().summonData.battleStats;
+    const player = game.scene.getPlayerPokemon()!.summonData.battleStats;
 
     expect(player[BattleStat.ATK]).toBe(0);
     expect(player[BattleStat.SPD]).toBe(0);
diff --git a/src/test/moves/u_turn.test.ts b/src/test/moves/u_turn.test.ts
index c54a94dde2b..2c12a4da43b 100644
--- a/src/test/moves/u_turn.test.ts
+++ b/src/test/moves/u_turn.test.ts
@@ -43,7 +43,7 @@ describe("Moves - U-turn", () => {
       Species.RAICHU,
       Species.SHUCKLE
     ]);
-    game.scene.getPlayerPokemon().hp = playerHp;
+    game.scene.getPlayerPokemon()!.hp = playerHp;
 
     // act
     game.doAttack(getMovePosition(game.scene, 0, Moves.U_TURN));
@@ -53,7 +53,7 @@ describe("Moves - U-turn", () => {
     // assert
     expect(game.scene.getParty()[1].hp).toEqual(Math.floor(game.scene.getParty()[1].getMaxHp() * 0.33 + playerHp));
     expect(game.phaseInterceptor.log).toContain("SwitchSummonPhase");
-    expect(game.scene.getPlayerPokemon().species.speciesId).toBe(Species.SHUCKLE);
+    expect(game.scene.getPlayerPokemon()!.species.speciesId).toBe(Species.SHUCKLE);
   }, 20000);
 
   it("triggers rough skin on the u-turn user before a new pokemon is switched in", async() => {
@@ -70,9 +70,10 @@ describe("Moves - U-turn", () => {
     await game.phaseInterceptor.to(SwitchPhase, false);
 
     // assert
-    expect(game.scene.getPlayerPokemon().hp).not.toEqual(game.scene.getPlayerPokemon().getMaxHp());
-    expect(game.scene.getEnemyPokemon().battleData.abilityRevealed).toBe(true); // proxy for asserting ability activated
-    expect(game.scene.getPlayerPokemon().species.speciesId).toEqual(Species.RAICHU);
+    const playerPkm = game.scene.getPlayerPokemon()!;
+    expect(playerPkm.hp).not.toEqual(playerPkm.getMaxHp());
+    expect(game.scene.getEnemyPokemon()!.battleData.abilityRevealed).toBe(true); // proxy for asserting ability activated
+    expect(playerPkm.species.speciesId).toEqual(Species.RAICHU);
     expect(game.phaseInterceptor.log).not.toContain("SwitchSummonPhase");
   }, 20000);
 
@@ -83,16 +84,17 @@ describe("Moves - U-turn", () => {
       Species.RAICHU,
       Species.SHUCKLE
     ]);
-    vi.spyOn(game.scene.getEnemyPokemon(), "randSeedInt").mockReturnValue(0);
+    vi.spyOn(game.scene.getEnemyPokemon()!, "randSeedInt").mockReturnValue(0);
 
     // act
     game.doAttack(getMovePosition(game.scene, 0, Moves.U_TURN));
     await game.phaseInterceptor.to(SwitchPhase, false);
 
     // assert
-    expect(game.scene.getPlayerPokemon().status?.effect).toEqual(StatusEffect.POISON);
-    expect(game.scene.getPlayerPokemon().species.speciesId).toEqual(Species.RAICHU);
-    expect(game.scene.getEnemyPokemon().battleData.abilityRevealed).toBe(true); // proxy for asserting ability activated
+    const playerPkm = game.scene.getPlayerPokemon()!;
+    expect(playerPkm.status?.effect).toEqual(StatusEffect.POISON);
+    expect(playerPkm.species.speciesId).toEqual(Species.RAICHU);
+    expect(game.scene.getEnemyPokemon()!.battleData.abilityRevealed).toBe(true); // proxy for asserting ability activated
     expect(game.phaseInterceptor.log).not.toContain("SwitchSummonPhase");
   }, 20000);
 });
diff --git a/src/test/settingMenu/helpers/menuManip.ts b/src/test/settingMenu/helpers/menuManip.ts
index f33867476cf..4fd5f526897 100644
--- a/src/test/settingMenu/helpers/menuManip.ts
+++ b/src/test/settingMenu/helpers/menuManip.ts
@@ -70,7 +70,7 @@ export class MenuManip {
   weWantThisBindInstead(keycode) {
     this.keycode = Phaser.Input.Keyboard.KeyCodes[keycode];
     const icon = getIconWithKeycode(this.config, this.keycode);
-    const key = getKeyWithKeycode(this.config, this.keycode);
+    const key = getKeyWithKeycode(this.config, this.keycode)!; // TODO: is this bang correct?
     const _keys = key.toLowerCase().split("_");
     const iconIdentifier = _keys[_keys.length-1];
     expect(icon.toLowerCase().includes(iconIdentifier)).toEqual(true);
@@ -78,7 +78,7 @@ export class MenuManip {
   }
 
   whenWeDelete(settingName?: string) {
-    this.settingName = SettingKeyboard[settingName] || this.settingName;
+    this.settingName = settingName ? SettingKeyboard[settingName] : this.settingName;
     // const key = getKeyWithSettingName(this.config, this.settingName);
     deleteBind(this.config, this.settingName);
     // expect(this.config.custom[key]).toEqual(-1);
@@ -86,7 +86,7 @@ export class MenuManip {
   }
 
   whenWeTryToDelete(settingName?: string) {
-    this.settingName = SettingKeyboard[settingName] || this.settingName;
+    this.settingName = settingName ? SettingKeyboard[settingName] : this.settingName;
     deleteBind(this.config, this.settingName);
     return this;
   }
diff --git a/src/test/settingMenu/rebinding_setting.test.ts b/src/test/settingMenu/rebinding_setting.test.ts
index 3bc17109c95..eead23972c2 100644
--- a/src/test/settingMenu/rebinding_setting.test.ts
+++ b/src/test/settingMenu/rebinding_setting.test.ts
@@ -37,13 +37,13 @@ describe("Test Rebinding", () => {
     expect(button).toEqual(Button.LEFT);
   });
   it("Check key for Keyboard KeyCode", () => {
-    const key = getKeyWithKeycode(config, Phaser.Input.Keyboard.KeyCodes.LEFT);
+    const key = getKeyWithKeycode(config, Phaser.Input.Keyboard.KeyCodes.LEFT) ?? "";
     const settingName = config.custom[key];
     const button = config.settings[settingName];
     expect(button).toEqual(Button.LEFT);
   });
   it("Check key for currenly Assigned to action not alt", () => {
-    const key = getKeyWithKeycode(config, Phaser.Input.Keyboard.KeyCodes.A);
+    const key = getKeyWithKeycode(config, Phaser.Input.Keyboard.KeyCodes.A) ?? "";
     const settingName = config.custom[key];
     const button = config.settings[settingName];
     expect(button).toEqual(Button.LEFT);
@@ -66,25 +66,25 @@ describe("Test Rebinding", () => {
   });
   it("Check icon for currenly Assigned to key code", () => {
     const keycode = Phaser.Input.Keyboard.KeyCodes.LEFT;
-    const key = getKeyWithKeycode(config, keycode);
+    const key = getKeyWithKeycode(config, keycode) ?? "";
     const icon = config.icons[key];
     expect(icon).toEqual("KEY_ARROW_LEFT.png");
   });
   it("Check icon for currenly Assigned to key code", () => {
     const keycode = Phaser.Input.Keyboard.KeyCodes.A;
-    const key = getKeyWithKeycode(config, keycode);
+    const key = getKeyWithKeycode(config, keycode) ?? "";
     const icon = config.icons[key];
     expect(icon).toEqual("A.png");
   });
   it("Check icon for currenly Assigned to setting name", () => {
     const settingName = SettingKeyboard.Button_Left;
-    const key = getKeyWithSettingName(config, settingName);
+    const key = getKeyWithSettingName(config, settingName) ?? "";
     const icon = config.icons[key];
     expect(icon).toEqual("KEY_ARROW_LEFT.png");
   });
   it("Check icon for currenly Assigned to setting name alt", () => {
     const settingName = SettingKeyboard.Alt_Button_Left;
-    const key = getKeyWithSettingName(config, settingName);
+    const key = getKeyWithSettingName(config, settingName) ?? "";
     const icon = config.icons[key];
     expect(icon).toEqual("A.png");
   });
@@ -369,7 +369,7 @@ describe("Test Rebinding", () => {
 
   it("test keyboard listener", () => {
     const keyDown = Phaser.Input.Keyboard.KeyCodes.S;
-    const key = getKeyWithKeycode(config, keyDown);
+    const key = getKeyWithKeycode(config, keyDown) ?? "";
     const settingName = config.custom[key];
     const buttonDown = config.settings[settingName];
     expect(buttonDown).toEqual(Button.DOWN);
diff --git a/src/test/sprites/pokemonSprite.test.ts b/src/test/sprites/pokemonSprite.test.ts
index ce847751b6b..deb5844d677 100644
--- a/src/test/sprites/pokemonSprite.test.ts
+++ b/src/test/sprites/pokemonSprite.test.ts
@@ -23,9 +23,12 @@ describe("check if every variant's sprite are correctly set", () => {
     expVariant = masterlist.exp;
     femaleVariant = masterlist.female;
     backVariant = masterlist.back;
-    delete masterlist.exp;
-    delete masterlist.female;
-    delete masterlist.back;
+    //@ts-ignore
+    delete masterlist.exp; //TODO: resolve ts-ignore
+    //@ts-ignore
+    delete masterlist.female; //TODO: resolve ts-ignore
+    //@ts-ignore
+    delete masterlist.back; //TODO: resolve ts-ignore
   });
 
   it("data should not be undefined", () => {
@@ -103,7 +106,7 @@ describe("check if every variant's sprite are correctly set", () => {
   }
 
   function getMissingFiles(keys: Record<string, any>, dirPath: string): string[] {
-    const errors = [];
+    const errors: string[] = [];
     for (const key of Object.keys(keys)) {
       const row = keys[key];
       for (const [index, elm] of row.entries()) {
diff --git a/src/test/ui/starter-select.test.ts b/src/test/ui/starter-select.test.ts
index eae5b3fe3a5..b61338bfcad 100644
--- a/src/test/ui/starter-select.test.ts
+++ b/src/test/ui/starter-select.test.ts
@@ -55,8 +55,8 @@ describe("UI - Starter select", () => {
       game.phaseInterceptor.unlock();
     });
     await game.phaseInterceptor.run(SelectStarterPhase);
-    let options: OptionSelectItem[];
-    let optionSelectUiHandler: OptionSelectUiHandler;
+    let options: OptionSelectItem[] = [];
+    let optionSelectUiHandler: OptionSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.OPTION_SELECT, () => {
         optionSelectUiHandler = game.scene.ui.getHandler() as OptionSelectUiHandler;
@@ -69,7 +69,7 @@ describe("UI - Starter select", () => {
     expect(options.some(option => option.label === "Manage Moves")).toBe(true);
     expect(options.some(option => option.label === "Use Candies")).toBe(true);
     expect(options.some(option => option.label === "Cancel")).toBe(true);
-    optionSelectUiHandler.processInput(Button.ACTION);
+    optionSelectUiHandler?.processInput(Button.ACTION);
 
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.STARTER_SELECT, () => {
@@ -116,8 +116,8 @@ describe("UI - Starter select", () => {
       game.phaseInterceptor.unlock();
     });
     await game.phaseInterceptor.run(SelectStarterPhase);
-    let options: OptionSelectItem[];
-    let optionSelectUiHandler: OptionSelectUiHandler;
+    let options: OptionSelectItem[] = [];
+    let optionSelectUiHandler: OptionSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.OPTION_SELECT, () => {
         optionSelectUiHandler = game.scene.ui.getHandler() as OptionSelectUiHandler;
@@ -130,7 +130,7 @@ describe("UI - Starter select", () => {
     expect(options.some(option => option.label === "Manage Moves")).toBe(true);
     expect(options.some(option => option.label === "Use Candies")).toBe(true);
     expect(options.some(option => option.label === "Cancel")).toBe(true);
-    optionSelectUiHandler.processInput(Button.ACTION);
+    optionSelectUiHandler?.processInput(Button.ACTION);
 
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.STARTER_SELECT, () => {
@@ -180,8 +180,8 @@ describe("UI - Starter select", () => {
       game.phaseInterceptor.unlock();
     });
     await game.phaseInterceptor.run(SelectStarterPhase);
-    let options: OptionSelectItem[];
-    let optionSelectUiHandler: OptionSelectUiHandler;
+    let options: OptionSelectItem[] = [];
+    let optionSelectUiHandler: OptionSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.OPTION_SELECT, () => {
         optionSelectUiHandler = game.scene.ui.getHandler() as OptionSelectUiHandler;
@@ -194,7 +194,7 @@ describe("UI - Starter select", () => {
     expect(options.some(option => option.label === "Manage Moves")).toBe(true);
     expect(options.some(option => option.label === "Use Candies")).toBe(true);
     expect(options.some(option => option.label === "Cancel")).toBe(true);
-    optionSelectUiHandler.processInput(Button.ACTION);
+    optionSelectUiHandler?.processInput(Button.ACTION);
 
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.STARTER_SELECT, () => {
@@ -242,8 +242,8 @@ describe("UI - Starter select", () => {
       game.phaseInterceptor.unlock();
     });
     await game.phaseInterceptor.run(SelectStarterPhase);
-    let options: OptionSelectItem[];
-    let optionSelectUiHandler: OptionSelectUiHandler;
+    let options: OptionSelectItem[] = [];
+    let optionSelectUiHandler: OptionSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.OPTION_SELECT, () => {
         optionSelectUiHandler = game.scene.ui.getHandler() as OptionSelectUiHandler;
@@ -256,7 +256,7 @@ describe("UI - Starter select", () => {
     expect(options.some(option => option.label === "Manage Moves")).toBe(true);
     expect(options.some(option => option.label === "Use Candies")).toBe(true);
     expect(options.some(option => option.label === "Cancel")).toBe(true);
-    optionSelectUiHandler.processInput(Button.ACTION);
+    optionSelectUiHandler?.processInput(Button.ACTION);
 
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.STARTER_SELECT, () => {
@@ -303,8 +303,8 @@ describe("UI - Starter select", () => {
       game.phaseInterceptor.unlock();
     });
     await game.phaseInterceptor.run(SelectStarterPhase);
-    let options: OptionSelectItem[];
-    let optionSelectUiHandler: OptionSelectUiHandler;
+    let options: OptionSelectItem[] = [];
+    let optionSelectUiHandler: OptionSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.OPTION_SELECT, () => {
         optionSelectUiHandler = game.scene.ui.getHandler() as OptionSelectUiHandler;
@@ -317,7 +317,7 @@ describe("UI - Starter select", () => {
     expect(options.some(option => option.label === "Manage Moves")).toBe(true);
     expect(options.some(option => option.label === "Use Candies")).toBe(true);
     expect(options.some(option => option.label === "Cancel")).toBe(true);
-    optionSelectUiHandler.processInput(Button.ACTION);
+    optionSelectUiHandler?.processInput(Button.ACTION);
 
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.STARTER_SELECT, () => {
@@ -364,8 +364,8 @@ describe("UI - Starter select", () => {
       game.phaseInterceptor.unlock();
     });
     await game.phaseInterceptor.run(SelectStarterPhase);
-    let options: OptionSelectItem[];
-    let optionSelectUiHandler: OptionSelectUiHandler;
+    let options: OptionSelectItem[] = [];
+    let optionSelectUiHandler: OptionSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.OPTION_SELECT, () => {
         optionSelectUiHandler = game.scene.ui.getHandler() as OptionSelectUiHandler;
@@ -378,7 +378,7 @@ describe("UI - Starter select", () => {
     expect(options.some(option => option.label === "Manage Moves")).toBe(true);
     expect(options.some(option => option.label === "Use Candies")).toBe(true);
     expect(options.some(option => option.label === "Cancel")).toBe(true);
-    optionSelectUiHandler.processInput(Button.ACTION);
+    optionSelectUiHandler?.processInput(Button.ACTION);
 
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.STARTER_SELECT, () => {
@@ -426,8 +426,8 @@ describe("UI - Starter select", () => {
       game.phaseInterceptor.unlock();
     });
     await game.phaseInterceptor.run(SelectStarterPhase);
-    let options: OptionSelectItem[];
-    let optionSelectUiHandler: OptionSelectUiHandler;
+    let options: OptionSelectItem[] = [];
+    let optionSelectUiHandler: OptionSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.OPTION_SELECT, () => {
         optionSelectUiHandler = game.scene.ui.getHandler() as OptionSelectUiHandler;
@@ -440,7 +440,7 @@ describe("UI - Starter select", () => {
     expect(options.some(option => option.label === "Manage Moves")).toBe(true);
     expect(options.some(option => option.label === "Use Candies")).toBe(true);
     expect(options.some(option => option.label === "Cancel")).toBe(true);
-    optionSelectUiHandler.processInput(Button.ACTION);
+    optionSelectUiHandler?.processInput(Button.ACTION);
 
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.STARTER_SELECT, () => {
@@ -486,8 +486,8 @@ describe("UI - Starter select", () => {
       game.phaseInterceptor.unlock();
     });
     await game.phaseInterceptor.run(SelectStarterPhase);
-    let options: OptionSelectItem[];
-    let optionSelectUiHandler: OptionSelectUiHandler;
+    let options: OptionSelectItem[] = [];
+    let optionSelectUiHandler: OptionSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.OPTION_SELECT, () => {
         optionSelectUiHandler = game.scene.ui.getHandler() as OptionSelectUiHandler;
@@ -500,7 +500,7 @@ describe("UI - Starter select", () => {
     expect(options.some(option => option.label === "Manage Moves")).toBe(true);
     expect(options.some(option => option.label === "Use Candies")).toBe(true);
     expect(options.some(option => option.label === "Cancel")).toBe(true);
-    optionSelectUiHandler.processInput(Button.ACTION);
+    optionSelectUiHandler?.processInput(Button.ACTION);
 
     let starterSelectUiHandler: StarterSelectUiHandler;
     await new Promise<void>((resolve) => {
@@ -551,8 +551,8 @@ describe("UI - Starter select", () => {
       game.phaseInterceptor.unlock();
     });
     await game.phaseInterceptor.run(SelectStarterPhase);
-    let options: OptionSelectItem[];
-    let optionSelectUiHandler: OptionSelectUiHandler;
+    let options: OptionSelectItem[] = [];
+    let optionSelectUiHandler: OptionSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.OPTION_SELECT, () => {
         optionSelectUiHandler = game.scene.ui.getHandler() as OptionSelectUiHandler;
@@ -565,9 +565,9 @@ describe("UI - Starter select", () => {
     expect(options.some(option => option.label === "Manage Moves")).toBe(true);
     expect(options.some(option => option.label === "Use Candies")).toBe(true);
     expect(options.some(option => option.label === "Cancel")).toBe(true);
-    optionSelectUiHandler.processInput(Button.ACTION);
+    optionSelectUiHandler?.processInput(Button.ACTION);
 
-    let starterSelectUiHandler: StarterSelectUiHandler;
+    let starterSelectUiHandler: StarterSelectUiHandler | undefined;
     await new Promise<void>((resolve) => {
       game.onNextPrompt("SelectStarterPhase", Mode.STARTER_SELECT, () => {
         starterSelectUiHandler = game.scene.ui.getHandler() as StarterSelectUiHandler;
@@ -576,11 +576,11 @@ describe("UI - Starter select", () => {
       });
     });
 
-    expect(starterSelectUiHandler.starterSpecies.length).toBe(1);
-    expect(starterSelectUiHandler.starterSpecies[0].generation).toBe(1);
-    expect(starterSelectUiHandler.starterSpecies[0].speciesId).toBe(32);
-    expect(starterSelectUiHandler.cursorObj.x).toBe(53);
-    expect(starterSelectUiHandler.cursorObj.y).toBe(31);
+    expect(starterSelectUiHandler?.starterSpecies.length).toBe(1);
+    expect(starterSelectUiHandler?.starterSpecies[0].generation).toBe(1);
+    expect(starterSelectUiHandler?.starterSpecies[0].speciesId).toBe(32);
+    expect(starterSelectUiHandler?.cursorObj.x).toBe(53);
+    expect(starterSelectUiHandler?.cursorObj.y).toBe(31);
 
     game.onNextPrompt("SelectStarterPhase", Mode.CONFIRM, () => {
       const handler = game.scene.ui.getHandler() as StarterSelectUiHandler;
diff --git a/src/test/utils/TextInterceptor.ts b/src/test/utils/TextInterceptor.ts
index a49f41f6be0..507161eb6d0 100644
--- a/src/test/utils/TextInterceptor.ts
+++ b/src/test/utils/TextInterceptor.ts
@@ -1,6 +1,6 @@
 export default class TextInterceptor {
   private scene;
-  public logs = [];
+  public logs: string[] = [];
   constructor(scene) {
     this.scene = scene;
     scene.messageWrapper = this;
@@ -17,6 +17,6 @@ export default class TextInterceptor {
   }
 
   getLatestMessage(): string {
-    return this.logs.pop();
+    return this.logs.pop() ?? "";
   }
 }
diff --git a/src/test/utils/gameManager.ts b/src/test/utils/gameManager.ts
index 842c6086058..771ab1e7081 100644
--- a/src/test/utils/gameManager.ts
+++ b/src/test/utils/gameManager.ts
@@ -81,7 +81,7 @@ export default class GameManager {
    * Ends the current phase.
    */
   endPhase() {
-    this.scene.getCurrentPhase().end();
+    this.scene.getCurrentPhase()?.end();
   }
 
   /**
@@ -174,7 +174,7 @@ export default class GameManager {
     // Confirm target selection if move is multi-target
     this.onNextPrompt("SelectTargetPhase", Mode.TARGET_SELECT, () => {
       const handler = this.scene.ui.getHandler() as TargetSelectUiHandler;
-      const move = (this.scene.getCurrentPhase() as SelectTargetPhase).getPokemon().getMoveset()[movePosition].getMove();
+      const move = (this.scene.getCurrentPhase() as SelectTargetPhase).getPokemon().getMoveset()[movePosition]!.getMove(); // TODO: is the bang correct?
       if (move.isMultiTarget()) {
         handler.processInput(Button.ACTION);
       }
@@ -255,7 +255,7 @@ export default class GameManager {
    */
   isCurrentPhase(phaseTarget) {
     const targetName = typeof phaseTarget === "string" ? phaseTarget : phaseTarget.name;
-    return this.scene.getCurrentPhase().constructor.name === targetName;
+    return this.scene.getCurrentPhase()?.constructor.name === targetName;
   }
 
   /**
@@ -278,7 +278,7 @@ export default class GameManager {
       await waitUntil(() => this.scene.ui?.getMode() === Mode.TITLE);
       await this.scene.gameData.tryExportData(GameDataType.SESSION, 0);
       await waitUntil(() => localStorage.hasOwnProperty("toExport"));
-      return resolve(localStorage.getItem("toExport"));
+      return resolve(localStorage.getItem("toExport")!); // TODO: is this bang correct?;
     });
   }
 
@@ -332,7 +332,7 @@ export default class GameManager {
   doRevivePokemon(pokemonIndex: number) {
     const party = this.scene.getParty();
     const candidate = new ModifierTypeOption(modifierTypes.MAX_REVIVE(), 0);
-    const modifier = candidate.type.newModifier(party[pokemonIndex]);
+    const modifier = candidate.type!.newModifier(party[pokemonIndex]);
     this.scene.addModifier(modifier, false);
   }
 
diff --git a/src/test/utils/gameManagerUtils.ts b/src/test/utils/gameManagerUtils.ts
index 74a73bb7875..dfba55fc75c 100644
--- a/src/test/utils/gameManagerUtils.ts
+++ b/src/test/utils/gameManagerUtils.ts
@@ -85,6 +85,7 @@ export function waitUntil(truth) {
 export function getMovePosition(scene: BattleScene, pokemonIndex: 0 | 1, move: Moves) {
   const playerPokemon = scene.getPlayerField()[pokemonIndex];
   const moveSet = playerPokemon.getMoveset();
-  const index = moveSet.findIndex((m) => m.moveId === move);
+  const index = moveSet.findIndex((m) => m?.moveId === move);
+  console.log(`Move position for ${Moves[move]} (=${move}):`, index);
   return index;
 }
diff --git a/src/test/utils/inputsHandler.ts b/src/test/utils/inputsHandler.ts
index e41667dc873..148329ada32 100644
--- a/src/test/utils/inputsHandler.ts
+++ b/src/test/utils/inputsHandler.ts
@@ -7,13 +7,17 @@ import TouchControl from "#app/touch-controls";
 import { JSDOM } from "jsdom";
 import fs from "fs";
 
+interface LogEntry {
+  type: string;
+  button: any;
+}
 
 export default class InputsHandler {
   private scene: BattleScene;
   private events: Phaser.Events.EventEmitter;
   private inputController: InputsController;
-  public log = [];
-  public logUp = [];
+  public log: LogEntry[] = [];
+  public logUp: LogEntry[] = [];
   private fakePad: Fakepad;
   private fakeMobile: FakeMobile;
 
@@ -22,7 +26,7 @@ export default class InputsHandler {
     this.inputController = this.scene.inputController;
     this.fakePad = new Fakepad(pad_xbox360);
     this.fakeMobile = new FakeMobile();
-    this.scene.input.gamepad.gamepads.push(this.fakePad);
+    this.scene.input.gamepad?.gamepads.push(this.fakePad);
     this.init();
   }
 
@@ -37,18 +41,18 @@ export default class InputsHandler {
 
   pressGamepadButton(button: integer, duration: integer): Promise<void> {
     return new Promise(async (resolve) => {
-      this.scene.input.gamepad.emit("down", this.fakePad, {index: button});
+      this.scene.input.gamepad?.emit("down", this.fakePad, {index: button});
       await holdOn(duration);
-      this.scene.input.gamepad.emit("up", this.fakePad, {index: button});
+      this.scene.input.gamepad?.emit("up", this.fakePad, {index: button});
       resolve();
     });
   }
 
   pressKeyboardKey(key: integer, duration: integer): Promise<void> {
     return new Promise(async (resolve) => {
-      this.scene.input.keyboard.emit("keydown", {keyCode: key});
+      this.scene.input.keyboard?.emit("keydown", {keyCode: key});
       await holdOn(duration);
-      this.scene.input.keyboard.emit("keyup", {keyCode: key});
+      this.scene.input.keyboard?.emit("keyup", {keyCode: key});
       resolve();
     });
   }
@@ -57,7 +61,7 @@ export default class InputsHandler {
     const touchControl = new TouchControl(this.scene);
     touchControl.deactivatePressedKey(); //test purpose
     this.events = this.inputController.events;
-    this.scene.input.gamepad.emit("connected", this.fakePad);
+    this.scene.input.gamepad?.emit("connected", this.fakePad);
     this.listenInputs();
   }
 
@@ -77,7 +81,8 @@ class Fakepad extends Phaser.Input.Gamepad.Gamepad {
   public index: number;
 
   constructor(pad) {
-    super(undefined, {...pad, buttons: pad.deviceMapping, axes: []});
+    //@ts-ignore
+    super(undefined, {...pad, buttons: pad.deviceMapping, axes: []}); //TODO: resolve ts-ignore
     this.id = "xbox_360_fakepad";
     this.index = 0;
   }
diff --git a/src/test/utils/mocks/mockClock.ts b/src/test/utils/mocks/mockClock.ts
index ba12dc002cc..3664a831305 100644
--- a/src/test/utils/mocks/mockClock.ts
+++ b/src/test/utils/mocks/mockClock.ts
@@ -2,7 +2,7 @@ import Clock = Phaser.Time.Clock;
 
 
 export class MockClock extends Clock {
-  public overrideDelay: number;
+  public overrideDelay: number | undefined;
   constructor(scene) {
     super(scene);
     this.overrideDelay = undefined;
diff --git a/src/test/utils/mocks/mockConsoleLog.ts b/src/test/utils/mocks/mockConsoleLog.ts
index 61c6c14b989..f44a0c7d6cd 100644
--- a/src/test/utils/mocks/mockConsoleLog.ts
+++ b/src/test/utils/mocks/mockConsoleLog.ts
@@ -1,12 +1,12 @@
 const MockConsoleLog = (_logDisabled= false, _phaseText=false) => {
-  let logs = [];
+  let logs: any[] = [];
   const logDisabled: boolean = _logDisabled;
   const phaseText: boolean = _phaseText;
   const originalLog = console.log;
   const originalError = console.error;
   const originalDebug = console.debug;
   const originalWarn = console.warn;
-  const notified = [];
+  const notified: any[] = [];
 
   const blacklist = ["Phaser", "variant icon does not exist", "Texture \"%s\" not found"];
   const whitelist = ["Phase"];
diff --git a/src/test/utils/mocks/mockGameObject.ts b/src/test/utils/mocks/mockGameObject.ts
new file mode 100644
index 00000000000..9138e0f687a
--- /dev/null
+++ b/src/test/utils/mocks/mockGameObject.ts
@@ -0,0 +1,3 @@
+export interface MockGameObject {
+
+}
diff --git a/src/test/utils/mocks/mockTextureManager.ts b/src/test/utils/mocks/mockTextureManager.ts
index 36a09efcf5a..95e8996836f 100644
--- a/src/test/utils/mocks/mockTextureManager.ts
+++ b/src/test/utils/mocks/mockTextureManager.ts
@@ -5,6 +5,7 @@ import MockNineslice from "#test/utils/mocks/mocksContainer/mockNineslice";
 import MockImage from "#test/utils/mocks/mocksContainer/mockImage";
 import MockText from "#test/utils/mocks/mocksContainer/mockText";
 import MockPolygon from "#test/utils/mocks/mocksContainer/mockPolygon";
+import { MockGameObject } from "./mockGameObject";
 
 
 export default class MockTextureManager {
@@ -12,7 +13,7 @@ export default class MockTextureManager {
   private scene;
   public add;
   public displayList;
-  public list = [];
+  public list: MockGameObject[] = [];
 
   constructor(scene) {
     this.scene = scene;
diff --git a/src/test/utils/mocks/mocksContainer/mockContainer.ts b/src/test/utils/mocks/mocksContainer/mockContainer.ts
index b74c46b4e86..d3672cb5235 100644
--- a/src/test/utils/mocks/mocksContainer/mockContainer.ts
+++ b/src/test/utils/mocks/mocksContainer/mockContainer.ts
@@ -1,6 +1,7 @@
 import MockTextureManager from "#test/utils/mocks/mockTextureManager";
+import { MockGameObject } from "../mockGameObject";
 
-export default class MockContainer {
+export default class MockContainer implements MockGameObject {
   protected x;
   protected y;
   protected scene;
@@ -11,7 +12,7 @@ export default class MockContainer {
   private style;
   public frame;
   protected textureManager;
-  public list = [];
+  public list: MockGameObject[] = [];
 
   constructor(textureManager: MockTextureManager, x, y) {
     this.x = x;
diff --git a/src/test/utils/mocks/mocksContainer/mockGraphics.ts b/src/test/utils/mocks/mocksContainer/mockGraphics.ts
index a08f150fe61..e026b212e16 100644
--- a/src/test/utils/mocks/mocksContainer/mockGraphics.ts
+++ b/src/test/utils/mocks/mocksContainer/mockGraphics.ts
@@ -1,6 +1,8 @@
-export default class MockGraphics {
+import { MockGameObject } from "../mockGameObject";
+
+export default class MockGraphics implements MockGameObject {
   private scene;
-  public list = [];
+  public list: MockGameObject[] = [];
   constructor(textureManager, config) {
     this.scene = textureManager.scene;
   }
diff --git a/src/test/utils/mocks/mocksContainer/mockRectangle.ts b/src/test/utils/mocks/mocksContainer/mockRectangle.ts
index db323268037..26c2f74ea42 100644
--- a/src/test/utils/mocks/mocksContainer/mockRectangle.ts
+++ b/src/test/utils/mocks/mocksContainer/mockRectangle.ts
@@ -1,7 +1,9 @@
-export default class MockRectangle {
+import { MockGameObject } from "../mockGameObject";
+
+export default class MockRectangle implements MockGameObject {
   private fillColor;
   private scene;
-  public list = [];
+  public list: MockGameObject[] = [];
 
   constructor(textureManager, x, y, width, height, fillColor) {
     this.fillColor = fillColor;
diff --git a/src/test/utils/mocks/mocksContainer/mockSprite.ts b/src/test/utils/mocks/mocksContainer/mockSprite.ts
index fb7f84741e8..9c566fc4bcb 100644
--- a/src/test/utils/mocks/mocksContainer/mockSprite.ts
+++ b/src/test/utils/mocks/mocksContainer/mockSprite.ts
@@ -1,9 +1,10 @@
+import { MockGameObject } from "../mockGameObject";
 import Sprite = Phaser.GameObjects.Sprite;
 import Frame = Phaser.Textures.Frame;
 import Phaser from "phaser";
 
 
-export default class MockSprite {
+export default class MockSprite implements MockGameObject {
   private phaserSprite;
   public pipelineData;
   public texture;
@@ -12,10 +13,11 @@ export default class MockSprite {
   public textureManager;
   public scene;
   public anims;
-  public list = [];
+  public list: MockGameObject[] = [];
   constructor(textureManager, x, y, texture) {
     this.textureManager = textureManager;
     this.scene = textureManager.scene;
+    // @ts-ignore
     Phaser.GameObjects.Sprite.prototype.setInteractive = this.setInteractive;
     // @ts-ignore
     Phaser.GameObjects.Sprite.prototype.setTexture = this.setTexture;
diff --git a/src/test/utils/mocks/mocksContainer/mockText.ts b/src/test/utils/mocks/mocksContainer/mockText.ts
index f4513e20926..5d405efadfd 100644
--- a/src/test/utils/mocks/mocksContainer/mockText.ts
+++ b/src/test/utils/mocks/mocksContainer/mockText.ts
@@ -1,12 +1,13 @@
 import UI from "#app/ui/ui";
+import { MockGameObject } from "../mockGameObject";
 
-export default class MockText {
+export default class MockText implements MockGameObject {
   private phaserText;
   private wordWrapWidth;
   private splitRegExp;
   private scene;
   private textureManager;
-  public list = [];
+  public list: MockGameObject[] = [];
   public style;
   public text = "";
 
diff --git a/src/test/utils/overridesHelper.ts b/src/test/utils/overridesHelper.ts
index e51928cc784..e77cd49b742 100644
--- a/src/test/utils/overridesHelper.ts
+++ b/src/test/utils/overridesHelper.ts
@@ -192,7 +192,7 @@ export class OverridesHelper {
    * @param battleType battle type to set
    * @returns this
    */
-  battleType(battleType: "single" | "double"): this {
+  battleType(battleType: "single" | "double" | null): this {
     vi.spyOn(Overrides, "BATTLE_TYPE_OVERRIDE", "get").mockReturnValue(battleType);
     this.log(`Battle type set to ${battleType} only!`);
     return this;
diff --git a/src/test/utils/phaseInterceptor.ts b/src/test/utils/phaseInterceptor.ts
index aabde643aa8..34f79f93b6e 100644
--- a/src/test/utils/phaseInterceptor.ts
+++ b/src/test/utils/phaseInterceptor.ts
@@ -289,7 +289,7 @@ export default class PhaseInterceptor {
   setMode(mode: Mode, ...args: any[]): Promise<void> {
     const currentPhase = this.scene.getCurrentPhase();
     const instance = this.scene.ui;
-    console.log("setMode", mode, args);
+    console.log("setMode", `${Mode[mode]} (=${mode})`, args);
     const ret = this.originalSetMode.apply(instance, [mode, ...args]);
     if (!this.phases[currentPhase.constructor.name]) {
       throw new Error(`missing ${currentPhase.constructor.name} in phaseInterceptior PHASES list`);
@@ -328,7 +328,7 @@ export default class PhaseInterceptor {
    * @param callback - The callback function to execute.
    * @param expireFn - The function to determine if the prompt has expired.
    */
-  addToNextPrompt(phaseTarget: string, mode: Mode, callback: () => void, expireFn: () => void, awaitingActionInput: boolean = false) {
+  addToNextPrompt(phaseTarget: string, mode: Mode, callback: () => void, expireFn?: () => void, awaitingActionInput: boolean = false) {
     this.prompts.push({
       phaseTarget,
       mode,
diff --git a/src/timed-event-manager.ts b/src/timed-event-manager.ts
index dac67bd7b4e..0502080d3a5 100644
--- a/src/timed-event-manager.ts
+++ b/src/timed-event-manager.ts
@@ -52,32 +52,32 @@ export class TimedEventManager {
     let multiplier = 1;
     const shinyEvents = timedEvents.filter((te) => te.eventType === EventType.SHINY && this.isActive(te));
     shinyEvents.forEach((se) => {
-      multiplier *= se.shinyMultiplier;
+      multiplier *= se.shinyMultiplier!; // TODO: is this bang correct?
     });
 
     return multiplier;
   }
 
   getEventBannerFilename(): string {
-    return timedEvents.find((te: TimedEvent) => this.isActive(te)).bannerFilename ?? null;
+    return timedEvents.find((te: TimedEvent) => this.isActive(te))?.bannerFilename!; // TODO: is this bang correct?
   }
 }
 
 export class TimedEventDisplay extends Phaser.GameObjects.Container {
-  private event: TimedEvent;
+  private event: TimedEvent | null;
   private eventTimerText: Phaser.GameObjects.Text;
   private banner: Phaser.GameObjects.Image;
   private bannerShadow: Phaser.GameObjects.Rectangle;
-  private eventTimer: NodeJS.Timeout;
+  private eventTimer: NodeJS.Timeout | null;
 
-  constructor(scene: BattleScene, x: number, y: number, event: TimedEvent) {
+  constructor(scene: BattleScene, x: number, y: number, event?: TimedEvent) {
     super(scene, x, y);
-    this.event = event;
+    this.event = event!; // TODO: is this bang correct?
     this.setVisible(false);
   }
 
   setup() {
-    this.banner = new Phaser.GameObjects.Image(this.scene, 29, 64, this.event.bannerFilename);
+    this.banner = new Phaser.GameObjects.Image(this.scene, 29, 64, this.event!.bannerFilename!); // TODO: are the bangs correct here?
     this.banner.setName("img-event-banner");
     this.banner.setOrigin(0, 0);
     this.banner.setScale(0.07);
@@ -97,7 +97,7 @@ export class TimedEventDisplay extends Phaser.GameObjects.Container {
       this.scene,
       this.banner.x + 8,
       this.banner.y + 100,
-      this.timeToGo(this.event.endDate),
+      this.timeToGo(this.event!.endDate), // TODO: is the bang correct here?
       TextStyle.WINDOW
     );
     this.eventTimerText.setName("text-event-timer");
@@ -118,7 +118,7 @@ export class TimedEventDisplay extends Phaser.GameObjects.Container {
 
   clear() {
     this.setVisible(false);
-    clearInterval(this.eventTimer);
+    this.eventTimer && clearInterval(this.eventTimer);
     this.eventTimer = null;
   }
 
@@ -145,6 +145,6 @@ export class TimedEventDisplay extends Phaser.GameObjects.Container {
   }
 
   updateCountdown() {
-    this.eventTimerText.setText(this.timeToGo(this.event.endDate));
+    this.eventTimerText.setText(this.timeToGo(this.event!.endDate)); // TODO: is the bang correct here?
   }
 }
diff --git a/src/touch-controls.ts b/src/touch-controls.ts
index 9953e99c81a..1726b47a4bd 100644
--- a/src/touch-controls.ts
+++ b/src/touch-controls.ts
@@ -48,7 +48,7 @@ export default class TouchControl {
 
     node.addEventListener("touchend", event => {
       event.preventDefault();
-      this.touchButtonUp(node, key, event.target["id"]);
+      this.touchButtonUp(node, key, event.target?.["id"]);
     });
   }
 
@@ -120,7 +120,7 @@ export default class TouchControl {
    * Prevent zoom on specified element
    * @param {HTMLElement} element
    */
-  preventElementZoom(element: HTMLElement): void {
+  preventElementZoom(element: HTMLElement | null): void {
     if (!element) {
       return;
     }
diff --git a/src/ui/ability-bar.ts b/src/ui/ability-bar.ts
index 7a4ae559975..b8259af9f3d 100644
--- a/src/ui/ability-bar.ts
+++ b/src/ui/ability-bar.ts
@@ -12,8 +12,8 @@ export default class AbilityBar extends Phaser.GameObjects.Container {
   private bg: Phaser.GameObjects.Image;
   private abilityBarText: Phaser.GameObjects.Text;
 
-  private tween: Phaser.Tweens.Tween;
-  private autoHideTimer: NodeJS.Timeout;
+  private tween: Phaser.Tweens.Tween | null;
+  private autoHideTimer: NodeJS.Timeout | null;
 
   public shown: boolean;
 
diff --git a/src/ui/abstact-option-select-ui-handler.ts b/src/ui/abstact-option-select-ui-handler.ts
index bf8a79ae194..f0148509220 100644
--- a/src/ui/abstact-option-select-ui-handler.ts
+++ b/src/ui/abstact-option-select-ui-handler.ts
@@ -36,7 +36,7 @@ export default abstract class AbstractOptionSelectUiHandler extends UiHandler {
   protected optionSelectText: Phaser.GameObjects.Text;
   protected optionSelectIcons: Phaser.GameObjects.Sprite[];
 
-  protected config: OptionSelectConfig;
+  protected config: OptionSelectConfig | null;
 
   protected blockInput: boolean;
 
@@ -44,10 +44,10 @@ export default abstract class AbstractOptionSelectUiHandler extends UiHandler {
 
   protected scale: number = 0.1666666667;
 
-  private cursorObj: Phaser.GameObjects.Image;
+  private cursorObj: Phaser.GameObjects.Image | null;
 
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
   }
 
   abstract getWindowWidth(): integer;
@@ -96,7 +96,7 @@ export default abstract class AbstractOptionSelectUiHandler extends UiHandler {
 
     this.optionSelectBg.width = Math.max(this.optionSelectText.displayWidth + 24, this.getWindowWidth());
 
-    if (this.config?.options.length > this.config?.maxOptions) {
+    if (this.config?.options && this.config?.options.length > (this.config?.maxOptions!)) { // TODO: is this bang correct?
       this.optionSelectText.setText(this.getOptionsWithScroll().map(o => o.label).join("\n"));
     }
 
@@ -123,8 +123,10 @@ export default abstract class AbstractOptionSelectUiHandler extends UiHandler {
 
           itemOverlayIcon.setPositionRelative(this.optionSelectText, 36 * this.scale, 7 + i * (114 * this.scale - 3));
 
-          itemIcon.setTint(argbFromRgba(Utils.rgbHexToRgba(option.itemArgs[0])));
-          itemOverlayIcon.setTint(argbFromRgba(Utils.rgbHexToRgba(option.itemArgs[1])));
+          if (option.itemArgs) {
+            itemIcon.setTint(argbFromRgba(Utils.rgbHexToRgba(option.itemArgs[0])));
+            itemOverlayIcon.setTint(argbFromRgba(Utils.rgbHexToRgba(option.itemArgs[1])));
+          }
         }
       }
     });
diff --git a/src/ui/achv-bar.ts b/src/ui/achv-bar.ts
index 05dde03aed7..0f3ab7c2e47 100644
--- a/src/ui/achv-bar.ts
+++ b/src/ui/achv-bar.ts
@@ -28,7 +28,7 @@ export default class AchvBar extends Phaser.GameObjects.Container {
     this.defaultWidth = 160;
     this.defaultHeight = 40;
 
-    this.bg = this.scene.add.nineslice(0, 0, "achv_bar", null, this.defaultWidth, this.defaultHeight, 41, 6, 16, 4);
+    this.bg = this.scene.add.nineslice(0, 0, "achv_bar", undefined, this.defaultWidth, this.defaultHeight, 41, 6, 16, 4);
     this.bg.setOrigin(0, 0);
 
     this.add(this.bg);
@@ -119,7 +119,8 @@ export default class AchvBar extends Phaser.GameObjects.Container {
         this.shown = false;
         this.setVisible(false);
         if (this.queue.length) {
-          this.showAchv(this.queue.shift());
+          const shifted = this.queue.shift();
+          shifted && this.showAchv(shifted);
         }
       }
     });
diff --git a/src/ui/achvs-ui-handler.ts b/src/ui/achvs-ui-handler.ts
index b5e17ce2b67..304b5df8340 100644
--- a/src/ui/achvs-ui-handler.ts
+++ b/src/ui/achvs-ui-handler.ts
@@ -19,10 +19,10 @@ export default class AchvsUiHandler extends MessageUiHandler {
   private scoreText: Phaser.GameObjects.Text;
   private unlockText: Phaser.GameObjects.Text;
 
-  private cursorObj: Phaser.GameObjects.NineSlice;
+  private cursorObj: Phaser.GameObjects.NineSlice | null;
 
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
   }
 
   setup() {
@@ -210,7 +210,7 @@ export default class AchvsUiHandler extends MessageUiHandler {
     let updateAchv = ret;
 
     if (!this.cursorObj) {
-      this.cursorObj = this.scene.add.nineslice(0, 0, "select_cursor_highlight", null, 16, 16, 1, 1, 1, 1);
+      this.cursorObj = this.scene.add.nineslice(0, 0, "select_cursor_highlight", undefined, 16, 16, 1, 1, 1, 1);
       this.cursorObj.setOrigin(0, 0);
       this.achvIconsContainer.add(this.cursorObj);
       updateAchv = true;
diff --git a/src/ui/awaitable-ui-handler.ts b/src/ui/awaitable-ui-handler.ts
index 18635b132f9..33be11ccc27 100644
--- a/src/ui/awaitable-ui-handler.ts
+++ b/src/ui/awaitable-ui-handler.ts
@@ -5,7 +5,7 @@ import {Button} from "#enums/buttons";
 
 export default abstract class AwaitableUiHandler extends UiHandler {
   protected awaitingActionInput: boolean;
-  protected onActionInput: Function;
+  protected onActionInput: Function | null;
   public tutorialActive: boolean = false;
 
   constructor(scene: BattleScene, mode: Mode) {
diff --git a/src/ui/ball-ui-handler.ts b/src/ui/ball-ui-handler.ts
index 9fc591f209f..d8b3e5e3ee8 100644
--- a/src/ui/ball-ui-handler.ts
+++ b/src/ui/ball-ui-handler.ts
@@ -13,7 +13,7 @@ export default class BallUiHandler extends UiHandler {
   private pokeballSelectBg: Phaser.GameObjects.NineSlice;
   private countsText: Phaser.GameObjects.Text;
 
-  private cursorObj: Phaser.GameObjects.Image;
+  private cursorObj: Phaser.GameObjects.Image | null;
 
   private scale: number = 0.1666666667;
 
diff --git a/src/ui/battle-info.ts b/src/ui/battle-info.ts
index d78b05a569f..98ebdf21078 100644
--- a/src/ui/battle-info.ts
+++ b/src/ui/battle-info.ts
@@ -22,12 +22,12 @@ export default class BattleInfo extends Phaser.GameObjects.Container {
   private boss: boolean;
   private bossSegments: integer;
   private offset: boolean;
-  private lastName: string;
+  private lastName: string | null;
   private lastTeraType: Type;
   private lastStatus: StatusEffect;
   private lastHp: integer;
   private lastMaxHp: integer;
-  private lastHpFrame: string;
+  private lastHpFrame: string | null;
   private lastExp: integer;
   private lastLevelExp: integer;
   private lastLevel: integer;
@@ -267,7 +267,7 @@ export default class BattleInfo extends Phaser.GameObjects.Container {
       this.add(this.effectivenessContainer);
 
       this.effectivenessText = addTextObject(this.scene, 5, 4.5, "", TextStyle.BATTLE_INFO);
-      this.effectivenessWindow = addWindow((this.scene as BattleScene), 0, 0, 0, 20, false, false, null, null, WindowVariant.XTHIN);
+      this.effectivenessWindow = addWindow((this.scene as BattleScene), 0, 0, 0, 20, undefined, false, undefined, undefined, WindowVariant.XTHIN);
 
       this.effectivenessContainer.add(this.effectivenessWindow);
       this.effectivenessContainer.add(this.effectivenessText);
@@ -293,7 +293,7 @@ export default class BattleInfo extends Phaser.GameObjects.Container {
     this.teraIcon.setVisible(this.lastTeraType !== Type.UNKNOWN);
     this.teraIcon.on("pointerover", () => {
       if (this.lastTeraType !== Type.UNKNOWN) {
-        (this.scene as BattleScene).ui.showTooltip(null, `${Utils.toReadableString(Type[this.lastTeraType])} Terastallized`);
+        (this.scene as BattleScene).ui.showTooltip("", `${Utils.toReadableString(Type[this.lastTeraType])} Terastallized`);
       }
     });
     this.teraIcon.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
@@ -303,7 +303,7 @@ export default class BattleInfo extends Phaser.GameObjects.Container {
     this.splicedIcon.setPositionRelative(this.nameText, nameTextWidth + this.genderText.displayWidth + 1 + (this.teraIcon.visible ? this.teraIcon.displayWidth + 1 : 0), 2.5);
     this.splicedIcon.setVisible(isFusion);
     if (this.splicedIcon.visible) {
-      this.splicedIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip(null, `${pokemon.species.getName(pokemon.formIndex)}/${pokemon.fusionSpecies.getName(pokemon.fusionFormIndex)}`));
+      this.splicedIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip("", `${pokemon.species.getName(pokemon.formIndex)}/${pokemon.fusionSpecies?.getName(pokemon.fusionFormIndex)}`));
       this.splicedIcon.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
     }
 
@@ -318,7 +318,7 @@ export default class BattleInfo extends Phaser.GameObjects.Container {
       const shinyDescriptor = doubleShiny || baseVariant ?
         `${baseVariant === 2 ? i18next.t("common:epicShiny") : baseVariant === 1 ? i18next.t("common:rareShiny") : i18next.t("common:commonShiny")}${doubleShiny ? `/${pokemon.fusionVariant === 2 ? i18next.t("common:epicShiny") : pokemon.fusionVariant === 1 ? i18next.t("common:rareShiny") : i18next.t("common:commonShiny")}` : ""}`
         : "";
-      this.shinyIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip(null, `${i18next.t("common:shinyOnHover")}${shinyDescriptor ? ` (${shinyDescriptor})` : ""}`));
+      this.shinyIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip("", `${i18next.t("common:shinyOnHover")}${shinyDescriptor ? ` (${shinyDescriptor})` : ""}`));
       this.shinyIcon.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
     }
 
@@ -330,7 +330,7 @@ export default class BattleInfo extends Phaser.GameObjects.Container {
 
     if (!this.player) {
       if (this.nameText.visible) {
-        this.nameText.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip(null, i18next.t("battleInfo:generation", { generation: i18next.t(`starterSelectUiHandler:gen${pokemon.species.generation}`) })));
+        this.nameText.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip("", i18next.t("battleInfo:generation", { generation: i18next.t(`starterSelectUiHandler:gen${pokemon.species.generation}`) })));
         this.nameText.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
       }
 
@@ -472,7 +472,7 @@ export default class BattleInfo extends Phaser.GameObjects.Container {
 
   updateBossSegmentDividers(pokemon: EnemyPokemon): void {
     while (this.hpBarSegmentDividers.length) {
-      this.hpBarSegmentDividers.pop().destroy();
+      this.hpBarSegmentDividers.pop()?.destroy();
     }
 
     if (this.boss && this.bossSegments > 1) {
@@ -768,7 +768,7 @@ export default class BattleInfo extends Phaser.GameObjects.Container {
     }
     this.currentEffectiveness = effectiveness;
 
-    if (!(this.scene as BattleScene).typeHints || effectiveness === undefined || this.flyoutMenu.flyoutVisible) {
+    if (!(this.scene as BattleScene).typeHints || effectiveness === undefined || this.flyoutMenu?.flyoutVisible) {
       this.effectivenessContainer.setVisible(false);
       return;
     }
diff --git a/src/ui/battle-message-ui-handler.ts b/src/ui/battle-message-ui-handler.ts
index f2da553c6da..6c5049394a7 100644
--- a/src/ui/battle-message-ui-handler.ts
+++ b/src/ui/battle-message-ui-handler.ts
@@ -147,19 +147,21 @@ export default class BattleMessageUiHandler extends MessageUiHandler {
         }
       }
     }
+
+    return false;
   }
 
   clear() {
     super.clear();
   }
 
-  showText(text: string, delay?: integer, callback?: Function, callbackDelay?: integer, prompt?: boolean, promptDelay?: integer) {
+  showText(text: string, delay?: integer | null, callback?: Function | null, callbackDelay?: integer | null, prompt?: boolean | null, promptDelay?: integer | null) {
     this.hideNameText();
     super.showText(text, delay, callback, callbackDelay, prompt, promptDelay);
   }
 
-  showDialogue(text: string, name: string, delay?: integer, callback?: Function, callbackDelay?: integer, prompt?: boolean, promptDelay?: integer) {
-    this.showNameText(name);
+  showDialogue(text: string, name?: string, delay?: integer | null, callback?: Function, callbackDelay?: integer, prompt?: boolean, promptDelay?: integer) {
+    name && this.showNameText(name);
     super.showDialogue(text, name, delay, callback, callbackDelay, prompt, promptDelay);
   }
 
@@ -180,7 +182,7 @@ export default class BattleMessageUiHandler extends MessageUiHandler {
       this.awaitingActionInput = true;
       this.onActionInput = () => {
         if (!showTotals) {
-          return this.promptLevelUpStats(partyMemberIndex, null, true).then(() => resolve());
+          return this.promptLevelUpStats(partyMemberIndex, [], true).then(() => resolve());
         } else {
           this.levelUpStatsContainer.setVisible(false);
           resolve();
@@ -206,8 +208,8 @@ export default class BattleMessageUiHandler extends MessageUiHandler {
                 highestIv = ivs[s];
               }
             });
-            shownStats.push(shownStat);
-            statsPool.splice(statsPool.indexOf(shownStat), 1);
+            shownStats.push(shownStat!); // TODO: is the bang correct?
+            statsPool.splice(statsPool.indexOf(shownStat!), 1); // TODO: is the bang correct?
           }
         } else {
           shownStats = stats;
@@ -228,7 +230,7 @@ export default class BattleMessageUiHandler extends MessageUiHandler {
   }
 
   getIvDescriptor(value: integer, typeIv: integer, pokemonId: integer): string {
-    const starterSpecies = this.scene.getPokemonById(pokemonId).species.getRootSpeciesId(true);
+    const starterSpecies = this.scene.getPokemonById(pokemonId)!.species.getRootSpeciesId(true); // TODO: is this bang correct?
     const starterIvs: number[] = this.scene.gameData.dexData[starterSpecies].ivs;
     const uiTheme = (this.scene as BattleScene).uiTheme; // Assuming uiTheme is accessible
 
diff --git a/src/ui/bgm-bar.ts b/src/ui/bgm-bar.ts
index 076eec26a8e..936ab91d8fa 100644
--- a/src/ui/bgm-bar.ts
+++ b/src/ui/bgm-bar.ts
@@ -24,7 +24,7 @@ export default class BgmBar extends Phaser.GameObjects.Container {
     this.defaultWidth = 230;
     this.defaultHeight = 100;
 
-    this.bg = this.scene.add.nineslice(-5, -5, "bgm_bar", null, this.defaultWidth, this.defaultHeight, 0, 0, 10, 10);
+    this.bg = this.scene.add.nineslice(-5, -5, "bgm_bar", undefined, this.defaultWidth, this.defaultHeight, 0, 0, 10, 10);
     this.bg.setOrigin(0, 0);
 
     this.add(this.bg);
diff --git a/src/ui/candy-bar.ts b/src/ui/candy-bar.ts
index 3a9f180dd59..5496ce9afce 100644
--- a/src/ui/candy-bar.ts
+++ b/src/ui/candy-bar.ts
@@ -11,8 +11,8 @@ export default class CandyBar extends Phaser.GameObjects.Container {
   private countText: Phaser.GameObjects.Text;
   private speciesId: Species;
 
-  private tween: Phaser.Tweens.Tween;
-  private autoHideTimer: NodeJS.Timeout;
+  private tween: Phaser.Tweens.Tween | null;
+  private autoHideTimer: NodeJS.Timeout | null;
 
   public shown: boolean;
 
@@ -21,7 +21,7 @@ export default class CandyBar extends Phaser.GameObjects.Container {
   }
 
   setup(): void {
-    this.bg = this.scene.add.nineslice(0, 0, "party_exp_bar", null, 8, 18, 21, 5, 6, 4);
+    this.bg = this.scene.add.nineslice(0, 0, "party_exp_bar", undefined, 8, 18, 21, 5, 6, 4);
     this.bg.setOrigin(0, 0);
 
     this.add(this.bg);
diff --git a/src/ui/challenges-select-ui-handler.ts b/src/ui/challenges-select-ui-handler.ts
index 6dcc359ef31..1200b3f3b40 100644
--- a/src/ui/challenges-select-ui-handler.ts
+++ b/src/ui/challenges-select-ui-handler.ts
@@ -30,12 +30,12 @@ export default class GameChallengesUiHandler extends UiHandler {
   private challengeLabels: Array<{ label: Phaser.GameObjects.Text, value: Phaser.GameObjects.Text }>;
   private monoTypeValue: Phaser.GameObjects.Sprite;
 
-  private cursorObj: Phaser.GameObjects.NineSlice;
+  private cursorObj: Phaser.GameObjects.NineSlice | null;
 
   private startCursor: Phaser.GameObjects.NineSlice;
 
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
   }
 
   setup() {
@@ -110,7 +110,7 @@ export default class GameChallengesUiHandler extends UiHandler {
     startText.setOrigin(0, 0);
     startText.setPositionRelative(startBg, 8, 4);
 
-    this.startCursor = this.scene.add.nineslice(0, 0, "summary_moves_cursor", null, (this.scene.game.canvas.width / 18) - 10, 16, 1, 1, 1, 1);
+    this.startCursor = this.scene.add.nineslice(0, 0, "summary_moves_cursor", undefined, (this.scene.game.canvas.width / 18) - 10, 16, 1, 1, 1, 1);
     this.startCursor.setName("9s-start-cursor");
     this.startCursor.setOrigin(0, 0);
     this.startCursor.setPositionRelative(startBg, 4, 4);
@@ -258,7 +258,7 @@ export default class GameChallengesUiHandler extends UiHandler {
       } else {
         this.scene.clearPhaseQueue();
         this.scene.pushPhase(new TitlePhase(this.scene));
-        this.scene.getCurrentPhase().end();
+        this.scene.getCurrentPhase()?.end();
       }
       success = true;
     } else if (button === Button.SUBMIT || button === Button.ACTION) {
@@ -267,7 +267,7 @@ export default class GameChallengesUiHandler extends UiHandler {
         const totalMinDifficulty = this.scene.gameMode.challenges.reduce((v, c) => v + c.getMinDifficulty(), 0);
         if (totalDifficulty >= totalMinDifficulty) {
           this.scene.unshiftPhase(new SelectStarterPhase(this.scene));
-          this.scene.getCurrentPhase().end();
+          this.scene.getCurrentPhase()?.end();
           success = true;
         } else {
           success = false;
@@ -354,7 +354,7 @@ export default class GameChallengesUiHandler extends UiHandler {
     let ret = super.setCursor(cursor);
 
     if (!this.cursorObj) {
-      this.cursorObj = this.scene.add.nineslice(0, 0, "summary_moves_cursor", null, (this.scene.game.canvas.width / 9) - 10, 16, 1, 1, 1, 1);
+      this.cursorObj = this.scene.add.nineslice(0, 0, "summary_moves_cursor", undefined, (this.scene.game.canvas.width / 9) - 10, 16, 1, 1, 1, 1);
       this.cursorObj.setOrigin(0, 0);
       this.valuesContainer.add(this.cursorObj);
     }
diff --git a/src/ui/command-ui-handler.ts b/src/ui/command-ui-handler.ts
index f083acd2f5b..11814a25240 100644
--- a/src/ui/command-ui-handler.ts
+++ b/src/ui/command-ui-handler.ts
@@ -17,7 +17,7 @@ export enum Command {
 
 export default class CommandUiHandler extends UiHandler {
   private commandsContainer: Phaser.GameObjects.Container;
-  private cursorObj: Phaser.GameObjects.Image;
+  private cursorObj: Phaser.GameObjects.Image | null;
 
   protected fieldIndex: integer = 0;
   protected cursor2: integer = 0;
diff --git a/src/ui/daily-run-scoreboard.ts b/src/ui/daily-run-scoreboard.ts
index 212d7b2a66c..b535a94d35c 100644
--- a/src/ui/daily-run-scoreboard.ts
+++ b/src/ui/daily-run-scoreboard.ts
@@ -59,14 +59,14 @@ export class DailyRunScoreboard extends Phaser.GameObjects.Container {
   }
 
   setup() {
-    const titleWindow = addWindow(this.scene, 0, 0, 114, 18, false, false, null, null, WindowVariant.THIN);
+    const titleWindow = addWindow(this.scene, 0, 0, 114, 18, false, false, undefined, undefined, WindowVariant.THIN);
     this.add(titleWindow);
 
     this.titleLabel = addTextObject(this.scene, titleWindow.displayWidth / 2, titleWindow.displayHeight / 2, i18next.t("menu:loading"), TextStyle.WINDOW, { fontSize: "64px" });
     this.titleLabel.setOrigin(0.5, 0.5);
     this.add(this.titleLabel);
 
-    const window = addWindow(this.scene, 0, 17, 114, 118, false, false, null, null, WindowVariant.THIN);
+    const window = addWindow(this.scene, 0, 17, 114, 118, false, false, undefined, undefined, WindowVariant.THIN);
     this.add(window);
 
     this.rankingsContainer = this.scene.add.container(6, 21);
diff --git a/src/ui/dropdown.ts b/src/ui/dropdown.ts
index 80935d16a71..f1723559b57 100644
--- a/src/ui/dropdown.ts
+++ b/src/ui/dropdown.ts
@@ -233,9 +233,9 @@ export class DropDownOption extends Phaser.GameObjects.Container {
   /**
    * @returns the x position to use for the current label depending on if it has a sprite or not
    */
-  getCurrentLabelX(): number {
+  getCurrentLabelX(): number | undefined {
     if (this.labels[this.currentLabelIndex].sprite) {
-      return this.labels[this.currentLabelIndex].sprite.x;
+      return this.labels[this.currentLabelIndex].sprite?.x;
     }
     return this.text.x;
   }
@@ -313,7 +313,7 @@ export class DropDown extends Phaser.GameObjects.Container {
       }
     });
 
-    this.window = addWindow(scene, 0, 0, optionWidth, options[options.length - 1].y + optionHeight + optionPaddingY, false, false, null, null, WindowVariant.XTHIN);
+    this.window = addWindow(scene, 0, 0, optionWidth, options[options.length - 1].y + optionHeight + optionPaddingY, false, false, undefined, undefined, WindowVariant.XTHIN);
     this.add(this.window);
     this.add(options);
     this.add(this.cursorObj);
@@ -465,7 +465,7 @@ export class DropDown extends Phaser.GameObjects.Container {
    * - the settings dictionary is like this { val: any, state: DropDownState, cursor: boolean, dir: SortDirection }
    */
   private getSettings(): any[] {
-    const settings = [];
+    const settings : any[] = [];
     for (let i = 0; i < this.options.length; i++) {
       settings.push({ val: this.options[i].val, state: this.options[i].state , cursor: (this.cursor === i), dir: this.options[i].dir });
     }
@@ -570,7 +570,7 @@ export class DropDown extends Phaser.GameObjects.Container {
       const optionWidth = this.options[i].getWidth();
       if (optionWidth > maxWidth) {
         maxWidth = optionWidth;
-        x = this.options[i].getCurrentLabelX();
+        x = this.options[i].getCurrentLabelX() ?? 0;
       }
     }
     this.window.width = maxWidth + x - this.window.x + 6;
diff --git a/src/ui/egg-gacha-ui-handler.ts b/src/ui/egg-gacha-ui-handler.ts
index 61031ba1c5c..92f3aaea1a4 100644
--- a/src/ui/egg-gacha-ui-handler.ts
+++ b/src/ui/egg-gacha-ui-handler.ts
@@ -60,7 +60,7 @@ export default class EggGachaUiHandler extends MessageUiHandler {
     this.eggGachaContainer.setVisible(false);
     ui.add(this.eggGachaContainer);
 
-    const bg = this.scene.add.nineslice(0, 0, "default_bg", null, 320, 180, 0, 0, 16, 0);
+    const bg = this.scene.add.nineslice(0, 0, "default_bg", undefined, 320, 180, 0, 0, 16, 0);
     bg.setOrigin(0, 0);
 
     this.eggGachaContainer.add(bg);
@@ -99,7 +99,7 @@ export default class EggGachaUiHandler extends MessageUiHandler {
 
       const gachaInfoContainer = this.scene.add.container(160, 46);
 
-      const currentLanguage = i18next.resolvedLanguage;
+      const currentLanguage = i18next.resolvedLanguage!; // TODO: is this bang correct?
       let gachaTextStyle = TextStyle.WINDOW_ALT;
       let gachaX = 4;
       let gachaY = 0;
@@ -217,7 +217,7 @@ export default class EggGachaUiHandler extends MessageUiHandler {
       { multiplier: multiplierOne, description: `25 ${i18next.t("egg:pulls")}`, icon: getVoucherTypeIcon(VoucherType.GOLDEN) }
     ];
 
-    const { resolvedLanguage } = i18next;
+    const resolvedLanguage = i18next.resolvedLanguage!; // TODO: is this bang correct?
     const pullOptionsText = pullOptions.map(option =>{
       const desc = option.description.split(" ");
       if (desc[0].length < 2) {
@@ -335,7 +335,7 @@ export default class EggGachaUiHandler extends MessageUiHandler {
     return Utils.fixedInt(delay);
   }
 
-  pull(pullCount?: integer, count?: integer, eggs?: Egg[]): void {
+  pull(pullCount: integer = 0, count: integer = 0, eggs?: Egg[]): void {
     if (Overrides.EGG_GACHA_PULL_COUNT_OVERRIDE && !count) {
       pullCount = Overrides.EGG_GACHA_PULL_COUNT_OVERRIDE;
     }
@@ -345,10 +345,10 @@ export default class EggGachaUiHandler extends MessageUiHandler {
 
     const doPull = () => {
       if (this.transitionCancelled) {
-        return this.showSummary(eggs);
+        return this.showSummary(eggs!);
       }
 
-      const egg = this.scene.add.sprite(127, 75, "egg", `egg_${eggs[count].getKey()}`);
+      const egg = this.scene.add.sprite(127, 75, "egg", `egg_${eggs![count].getKey()}`);
       egg.setScale(0.5);
 
       this.gachaContainers[this.gachaCursor].add(egg);
@@ -391,7 +391,7 @@ export default class EggGachaUiHandler extends MessageUiHandler {
                           if (++count < pullCount) {
                             this.pull(pullCount, count, eggs);
                           } else {
-                            this.showSummary(eggs);
+                            this.showSummary(eggs!);
                           }
                         }
                       });
@@ -584,7 +584,7 @@ export default class EggGachaUiHandler extends MessageUiHandler {
   }
 
   showError(text: string): void {
-    this.showText(text, null, () => this.showText(this.defaultText), Utils.fixedInt(1500));
+    this.showText(text, undefined, () => this.showText(this.defaultText), Utils.fixedInt(1500));
   }
 
   setTransitioning(transitioning: boolean): void {
diff --git a/src/ui/egg-hatch-scene-handler.ts b/src/ui/egg-hatch-scene-handler.ts
index 0e247da60ab..f567861e0b7 100644
--- a/src/ui/egg-hatch-scene-handler.ts
+++ b/src/ui/egg-hatch-scene-handler.ts
@@ -36,7 +36,7 @@ export default class EggHatchSceneHandler extends UiHandler {
   show(_args: any[]): boolean {
     super.show(_args);
 
-    this.getUi().showText(null, 0);
+    this.getUi().showText("", 0);
 
     this.scene.setModifiersVisible(false);
 
diff --git a/src/ui/evolution-scene-handler.ts b/src/ui/evolution-scene-handler.ts
index 64d190c4d3f..ffbd06afde3 100644
--- a/src/ui/evolution-scene-handler.ts
+++ b/src/ui/evolution-scene-handler.ts
@@ -83,6 +83,8 @@ export default class EvolutionSceneHandler extends MessageUiHandler {
         }
       }
     }
+
+    return false;
   }
 
   setCursor(_cursor: integer): boolean {
diff --git a/src/ui/fight-ui-handler.ts b/src/ui/fight-ui-handler.ts
index ed520512443..8279ab72a70 100644
--- a/src/ui/fight-ui-handler.ts
+++ b/src/ui/fight-ui-handler.ts
@@ -21,7 +21,7 @@ export default class FightUiHandler extends UiHandler {
   private powerText: Phaser.GameObjects.Text;
   private accuracyLabel: Phaser.GameObjects.Text;
   private accuracyText: Phaser.GameObjects.Text;
-  private cursorObj: Phaser.GameObjects.Image;
+  private cursorObj: Phaser.GameObjects.Image | null;
   private moveCategoryIcon: Phaser.GameObjects.Sprite;
 
   protected fieldIndex: integer = 0;
@@ -176,7 +176,7 @@ export default class FightUiHandler extends UiHandler {
     const hasMove = cursor < moveset.length;
 
     if (hasMove) {
-      const pokemonMove = moveset[cursor];
+      const pokemonMove = moveset[cursor]!; // TODO: is the bang correct?
       this.typeIcon.setTexture(`types${Utils.verifyLang(i18next.resolvedLanguage) ? `_${i18next.resolvedLanguage}` : ""}`, Type[pokemonMove.getMove().type].toLowerCase()).setScale(0.8);
       this.moveCategoryIcon.setTexture("categories", MoveCategory[pokemonMove.getMove().category].toLowerCase()).setScale(1.0);
 
@@ -246,7 +246,7 @@ export default class FightUiHandler extends UiHandler {
       moveText.setName("text-empty-move");
 
       if (moveIndex < moveset.length) {
-        const pokemonMove = moveset[moveIndex];
+        const pokemonMove = moveset[moveIndex]!; // TODO is the bang correct?
         moveText.setText(pokemonMove.getName());
         moveText.setName(pokemonMove.getName());
         moveText.setColor(this.getMoveColor(pokemon, pokemonMove) ?? moveText.style.color);
@@ -273,7 +273,7 @@ export default class FightUiHandler extends UiHandler {
 
     const moveColors = opponents.map((opponent) => {
       return opponent.getMoveEffectiveness(pokemon, pokemonMove);
-    }).sort((a, b) => b - a).map((effectiveness) => {
+    }).filter((eff) => !!eff).sort((a, b) => b - a).map((effectiveness) => {
       return getTypeDamageMultiplierColor(effectiveness, "offense");
     });
 
diff --git a/src/ui/filter-bar.ts b/src/ui/filter-bar.ts
index 52266a3a06b..31d7c562da2 100644
--- a/src/ui/filter-bar.ts
+++ b/src/ui/filter-bar.ts
@@ -31,7 +31,7 @@ export class FilterBar extends Phaser.GameObjects.Container {
     this.width = width;
     this.height = height;
 
-    this.window = addWindow(scene, 0, 0, width, height, false, false, null, null, WindowVariant.THIN);
+    this.window = addWindow(scene, 0, 0, width, height, false, false, undefined, undefined, WindowVariant.THIN);
     this.add(this.window);
 
     this.cursorObj = this.scene.add.image(1, 1, "cursor");
diff --git a/src/ui/form-modal-ui-handler.ts b/src/ui/form-modal-ui-handler.ts
index 2c576a0fbaa..a4539c2369f 100644
--- a/src/ui/form-modal-ui-handler.ts
+++ b/src/ui/form-modal-ui-handler.ts
@@ -17,7 +17,7 @@ export abstract class FormModalUiHandler extends ModalUiHandler {
   protected inputContainers: Phaser.GameObjects.Container[];
   protected inputs: InputText[];
   protected errorMessage: Phaser.GameObjects.Text;
-  protected submitAction: Function;
+  protected submitAction: Function | null;
   protected tween: Phaser.Tweens.Tween;
 
   constructor(scene: BattleScene, mode?: Mode) {
diff --git a/src/ui/game-stats-ui-handler.ts b/src/ui/game-stats-ui-handler.ts
index 8f1e8890a76..3d6d8081d4e 100644
--- a/src/ui/game-stats-ui-handler.ts
+++ b/src/ui/game-stats-ui-handler.ts
@@ -219,7 +219,7 @@ export default class GameStatsUiHandler extends UiHandler {
   private statValues: Phaser.GameObjects.Text[];
 
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
 
     this.statLabels = [];
     this.statValues = [];
@@ -299,7 +299,7 @@ export default class GameStatsUiHandler extends UiHandler {
     const statKeys = Object.keys(displayStats).slice(this.cursor * 2, this.cursor * 2 + 18);
     statKeys.forEach((key, s) => {
       const stat = displayStats[key] as DisplayStat;
-      const value = stat.sourceFunc(this.scene.gameData);
+      const value = stat.sourceFunc!(this.scene.gameData); // TODO: is this bang correct?
       this.statLabels[s].setText(!stat.hidden || isNaN(parseInt(value)) || parseInt(value) ? i18next.t(`gameStatsUiHandler:${stat.label_key}`) : "???");
       this.statValues[s].setText(value);
     });
diff --git a/src/ui/login-form-ui-handler.ts b/src/ui/login-form-ui-handler.ts
index 971bef6ea6b..450c583a26c 100644
--- a/src/ui/login-form-ui-handler.ts
+++ b/src/ui/login-form-ui-handler.ts
@@ -130,7 +130,7 @@ export default class LoginFormUiHandler extends FormModalUiHandler {
           .then(response => {
             if (response.hasOwnProperty("token")) {
               Utils.setCookie(Utils.sessionIdKey, response.token);
-              originalLoginAction();
+              originalLoginAction && originalLoginAction();
             } else {
               onFail(response);
             }
diff --git a/src/ui/menu-ui-handler.ts b/src/ui/menu-ui-handler.ts
index c0c5e69b893..27db60aa5da 100644
--- a/src/ui/menu-ui-handler.ts
+++ b/src/ui/menu-ui-handler.ts
@@ -38,7 +38,7 @@ export default class MenuUiHandler extends MessageUiHandler {
   private menuBg: Phaser.GameObjects.NineSlice;
   protected optionSelectText: Phaser.GameObjects.Text;
 
-  private cursorObj: Phaser.GameObjects.Image;
+  private cursorObj: Phaser.GameObjects.Image | null;
 
   private excludedMenus: () => ConditionalMenu[];
   private menuOptions: MenuOptions[];
@@ -52,7 +52,7 @@ export default class MenuUiHandler extends MessageUiHandler {
 
 
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
 
     this.excludedMenus = () => [
       { condition: [Mode.COMMAND, Mode.TITLE].includes(mode ?? Mode.TITLE), options: [ MenuOptions.EGG_GACHA, MenuOptions.EGG_LIST] },
@@ -69,7 +69,7 @@ export default class MenuUiHandler extends MessageUiHandler {
   setup(): void {
     const ui = this.getUi();
     // wiki url directs based on languges available on wiki
-    const lang = i18next.resolvedLanguage.substring(0,2);
+    const lang = i18next.resolvedLanguage?.substring(0,2)!; // TODO: is this bang correct?
     if (["de", "fr", "ko", "zh"].includes(lang)) {
       wikiUrl = `https://wiki.pokerogue.net/${lang}:start`;
     }
@@ -147,7 +147,7 @@ export default class MenuUiHandler extends MessageUiHandler {
 
     this.menuContainer.add(this.menuMessageBoxContainer);
 
-    const manageDataOptions = [];
+    const manageDataOptions: any[] = []; // TODO: proper type
 
     const confirmSlot = (message: string, slotFilter: (i: integer) => boolean, callback: (i: integer) => void) => {
       ui.revertMode();
@@ -159,7 +159,7 @@ export default class MenuUiHandler extends MessageUiHandler {
               handler: () => {
                 callback(i);
                 ui.revertMode();
-                ui.showText(null, 0);
+                ui.showText("", 0);
                 return true;
               }
             };
@@ -167,7 +167,7 @@ export default class MenuUiHandler extends MessageUiHandler {
             label: i18next.t("menuUiHandler:cancel"),
             handler: () => {
               ui.revertMode();
-              ui.showText(null, 0);
+              ui.showText("", 0);
               return true;
             }
           }]),
@@ -259,7 +259,7 @@ export default class MenuUiHandler extends MessageUiHandler {
       {
         label: "Wiki",
         handler: () => {
-          window.open(wikiUrl, "_blank").focus();
+          window.open(wikiUrl, "_blank")?.focus();
           return true;
         },
         keepOpen: true
@@ -267,7 +267,7 @@ export default class MenuUiHandler extends MessageUiHandler {
       {
         label: "Discord",
         handler: () => {
-          window.open(discordUrl, "_blank").focus();
+          window.open(discordUrl, "_blank")?.focus();
           return true;
         },
         keepOpen: true
@@ -275,7 +275,7 @@ export default class MenuUiHandler extends MessageUiHandler {
       {
         label: "GitHub",
         handler: () => {
-          window.open(githubUrl, "_blank").focus();
+          window.open(githubUrl, "_blank")?.focus();
           return true;
         },
         keepOpen: true
@@ -283,7 +283,7 @@ export default class MenuUiHandler extends MessageUiHandler {
       {
         label: "Reddit",
         handler: () => {
-          window.open(redditUrl, "_blank").focus();
+          window.open(redditUrl, "_blank")?.focus();
           return true;
         },
         keepOpen: true
@@ -386,7 +386,7 @@ export default class MenuUiHandler extends MessageUiHandler {
         if (!bypassLogin && !this.manageDataConfig.options.some(o => o.label === i18next.t("menuUiHandler:linkDiscord") || o.label === i18next.t("menuUiHandler:unlinkDiscord"))) {
           this.manageDataConfig.options.splice(this.manageDataConfig.options.length-1,0,
             {
-              label: loggedInUser.discordId === "" ? i18next.t("menuUiHandler:linkDiscord") : i18next.t("menuUiHandler:unlinkDiscord"),
+              label: loggedInUser?.discordId === "" ? i18next.t("menuUiHandler:linkDiscord") : i18next.t("menuUiHandler:unlinkDiscord"),
               handler: () => {
                 if (loggedInUser?.discordId === "") {
                   const token = Utils.getCookie(Utils.sessionIdKey);
@@ -442,7 +442,7 @@ export default class MenuUiHandler extends MessageUiHandler {
             ui.showText(i18next.t("menuUiHandler:losingProgressionWarning"), null, () => {
               ui.setOverlayMode(Mode.CONFIRM, () => this.scene.gameData.saveAll(this.scene, true, true, true, true).then(() => this.scene.reset(true)), () => {
                 ui.revertMode();
-                ui.showText(null, 0);
+                ui.showText("", 0);
               }, false, -98);
             });
           } else {
@@ -467,7 +467,7 @@ export default class MenuUiHandler extends MessageUiHandler {
           ui.showText(i18next.t("menuUiHandler:losingProgressionWarning"), null, () => {
             ui.setOverlayMode(Mode.CONFIRM, doLogout, () => {
               ui.revertMode();
-              ui.showText(null, 0);
+              ui.showText("", 0);
             }, false, -98);
           });
         } else {
diff --git a/src/ui/message-ui-handler.ts b/src/ui/message-ui-handler.ts
index 05c91ca1643..c870ef13a27 100644
--- a/src/ui/message-ui-handler.ts
+++ b/src/ui/message-ui-handler.ts
@@ -4,8 +4,8 @@ import { Mode } from "./ui";
 import * as Utils from "../utils";
 
 export default abstract class MessageUiHandler extends AwaitableUiHandler {
-  protected textTimer: Phaser.Time.TimerEvent;
-  protected textCallbackTimer: Phaser.Time.TimerEvent;
+  protected textTimer: Phaser.Time.TimerEvent | null;
+  protected textCallbackTimer: Phaser.Time.TimerEvent | null;
   public pendingPrompt: boolean;
 
   public message: Phaser.GameObjects.Text;
@@ -17,15 +17,15 @@ export default abstract class MessageUiHandler extends AwaitableUiHandler {
     this.pendingPrompt = false;
   }
 
-  showText(text: string, delay?: integer, callback?: Function, callbackDelay?: integer, prompt?: boolean, promptDelay?: integer) {
+  showText(text: string, delay?: integer | null, callback?: Function | null, callbackDelay?: integer | null, prompt?: boolean | null, promptDelay?: integer | null) {
     this.showTextInternal(text, delay, callback, callbackDelay, prompt, promptDelay);
   }
 
-  showDialogue(text: string, name: string, delay?: integer, callback?: Function, callbackDelay?: integer, prompt?: boolean, promptDelay?: integer) {
+  showDialogue(text: string, name?: string, delay?: integer | null, callback?: Function | null, callbackDelay?: integer | null, prompt?: boolean | null, promptDelay?: integer | null) {
     this.showTextInternal(text, delay, callback, callbackDelay, prompt, promptDelay);
   }
 
-  private showTextInternal(text: string, delay: integer, callback: Function, callbackDelay: integer, prompt: boolean, promptDelay: integer) {
+  private showTextInternal(text: string, delay?: integer | null, callback?: Function | null, callbackDelay?: integer | null, prompt?: boolean | null, promptDelay?: integer | null) {
     if (delay === null || delay === undefined) {
       delay = 20;
     }
@@ -33,7 +33,7 @@ export default abstract class MessageUiHandler extends AwaitableUiHandler {
     const delayMap = new Map<integer, integer>();
     const soundMap = new Map<integer, string>();
     const actionPattern = /@(c|d|s)\{(.*?)\}/;
-    let actionMatch: RegExpExecArray;
+    let actionMatch: RegExpExecArray | null;
     while ((actionMatch = actionPattern.exec(text))) {
       switch (actionMatch[1]) {
       case "c":
@@ -99,7 +99,7 @@ export default abstract class MessageUiHandler extends AwaitableUiHandler {
       this.textTimer = this.scene.time.addEvent({
         delay: delay,
         callback: () => {
-          const charIndex = text.length - this.textTimer.repeatCount;
+          const charIndex = text.length - (this.textTimer?.repeatCount!); // TODO: is this bang correct?
           const charVar = charVarMap.get(charIndex);
           const charSound = soundMap.get(charIndex);
           const charDelay = delayMap.get(charIndex);
@@ -111,7 +111,7 @@ export default abstract class MessageUiHandler extends AwaitableUiHandler {
             if (charSound) {
               this.scene.playSound(charSound);
             }
-            if (callback && !this.textTimer.repeatCount) {
+            if (callback && !this.textTimer?.repeatCount) {
               if (callbackDelay && !prompt) {
                 this.textCallbackTimer = this.scene.time.delayedCall(callbackDelay, () => {
                   if (this.textCallbackTimer) {
@@ -126,11 +126,11 @@ export default abstract class MessageUiHandler extends AwaitableUiHandler {
             }
           };
           if (charDelay) {
-            this.textTimer.paused = true;
+            this.textTimer!.paused = true; // TODO: is the bang correct?
             this.scene.tweens.addCounter({
               duration: Utils.getFrameMs(charDelay),
               onComplete: () => {
-                this.textTimer.paused = false;
+                this.textTimer!.paused = false; // TODO: is the bang correct?
                 advance();
               }
             });
@@ -151,7 +151,7 @@ export default abstract class MessageUiHandler extends AwaitableUiHandler {
     }
   }
 
-  showPrompt(callback: Function, callbackDelay: integer) {
+  showPrompt(callback?: Function | null, callbackDelay?: integer | null) {
     const wrappedTextLines = this.message.runWordWrap(this.message.text).split(/\n/g);
     const textLinesCount = wrappedTextLines.length;
     const lastTextLine = wrappedTextLines[wrappedTextLines.length - 1];
diff --git a/src/ui/modal-ui-handler.ts b/src/ui/modal-ui-handler.ts
index 85b20e423c3..5aac6ac194e 100644
--- a/src/ui/modal-ui-handler.ts
+++ b/src/ui/modal-ui-handler.ts
@@ -17,7 +17,7 @@ export abstract class ModalUiHandler extends UiHandler {
   protected buttonBgs: Phaser.GameObjects.NineSlice[];
 
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
 
     this.buttonContainers = [];
     this.buttonBgs = [];
diff --git a/src/ui/modifier-select-ui-handler.ts b/src/ui/modifier-select-ui-handler.ts
index 76cda280720..016708027ca 100644
--- a/src/ui/modifier-select-ui-handler.ts
+++ b/src/ui/modifier-select-ui-handler.ts
@@ -35,7 +35,7 @@ export default class ModifierSelectUiHandler extends AwaitableUiHandler {
   public options: ModifierOption[];
   public shopOptionsRows: ModifierOption[][];
 
-  private cursorObj: Phaser.GameObjects.Image;
+  private cursorObj: Phaser.GameObjects.Image | null;
 
   constructor(scene: BattleScene) {
     super(scene, Mode.CONFIRM);
@@ -53,9 +53,12 @@ export default class ModifierSelectUiHandler extends AwaitableUiHandler {
     const canvas = document.createElement("canvas");
     const context = canvas.getContext("2d");
     const styleOptions = getTextStyleOptions(TextStyle.PARTY, (this.scene as BattleScene).uiTheme).styleOptions;
-    context.font = styleOptions.fontSize + "px " + styleOptions.fontFamily;
-    this.transferButtonWidth = context.measureText(i18next.t("modifierSelectUiHandler:transfer")).width;
-    this.checkButtonWidth = context.measureText(i18next.t("modifierSelectUiHandler:checkTeam")).width;
+
+    if (context) {
+      context.font = styleOptions.fontSize + "px " + styleOptions.fontFamily;
+      this.transferButtonWidth = context.measureText(i18next.t("modifierSelectUiHandler:transfer")).width;
+      this.checkButtonWidth = context.measureText(i18next.t("modifierSelectUiHandler:checkTeam")).width;
+    }
 
     this.transferButtonContainer = this.scene.add.container((this.scene.game.canvas.width - this.checkButtonWidth) / 6 - 21, -64);
     this.transferButtonContainer.setName("transfer-btn");
@@ -394,7 +397,7 @@ export default class ModifierSelectUiHandler extends AwaitableUiHandler {
       }
 
       const type = options[this.cursor].modifierTypeOption.type;
-      ui.showText(type.getDescription(this.scene));
+      type && ui.showText(type.getDescription(this.scene));
       if (type instanceof TmModifierType) {
         // prepare the move overlay to be shown with the toggle
         this.moveInfoOverlay.show(allMoves[type.moveId]);
@@ -574,7 +577,7 @@ class ModifierOption extends Phaser.GameObjects.Container {
     this.add(this.itemContainer);
 
     const getItem = () => {
-      const item = this.scene.add.sprite(0, 0, "items", this.modifierTypeOption.type.iconImage);
+      const item = this.scene.add.sprite(0, 0, "items", this.modifierTypeOption.type?.iconImage);
       return item;
     };
 
@@ -587,10 +590,10 @@ class ModifierOption extends Phaser.GameObjects.Container {
       this.itemContainer.add(this.itemTint);
     }
 
-    this.itemText = addTextObject(this.scene, 0, 35, this.modifierTypeOption.type.name, TextStyle.PARTY, { align: "center" });
+    this.itemText = addTextObject(this.scene, 0, 35, this.modifierTypeOption.type?.name!, TextStyle.PARTY, { align: "center" }); // TODO: is this bang correct?
     this.itemText.setOrigin(0.5, 0);
     this.itemText.setAlpha(0);
-    this.itemText.setTint(getModifierTierTextTint(this.modifierTypeOption.type.tier));
+    this.itemText.setTint(this.modifierTypeOption.type?.tier ? getModifierTierTextTint(this.modifierTypeOption.type?.tier) : undefined);
     this.add(this.itemText);
 
     if (this.modifierTypeOption.cost) {
@@ -722,7 +725,7 @@ class ModifierOption extends Phaser.GameObjects.Container {
   }
 
   getPbAtlasKey(tierOffset: integer = 0) {
-    return getPokeballAtlasKey((this.modifierTypeOption.type.tier + tierOffset) as integer as PokeballType);
+    return getPokeballAtlasKey((this.modifierTypeOption.type?.tier! + tierOffset) as integer as PokeballType); // TODO: is this bang correct?
   }
 
   updateCostText(): void {
diff --git a/src/ui/move-info-overlay.ts b/src/ui/move-info-overlay.ts
index 3b947cb842d..ded19b01a12 100644
--- a/src/ui/move-info-overlay.ts
+++ b/src/ui/move-info-overlay.ts
@@ -30,7 +30,7 @@ export default class MoveInfoOverlay extends Phaser.GameObjects.Container implem
   private move: Move;
 
   private desc: Phaser.GameObjects.Text;
-  private descScroll : Phaser.Tweens.Tween = null;
+  private descScroll : Phaser.Tweens.Tween | null = null;
 
   private val: Phaser.GameObjects.Container;
   private pp:  Phaser.GameObjects.Text;
@@ -131,7 +131,7 @@ export default class MoveInfoOverlay extends Phaser.GameObjects.Container implem
   // show this component with infos for the specific move
   show(move : Move):boolean {
     if (!(this.scene as BattleScene).enableMoveInfo) {
-      return; // move infos have been disabled
+      return false; // move infos have been disabled // TODO:: is `false` correct? i used to be `undeefined`
     }
     this.move = move;
     this.pow.setText(move.power >= 0 ? move.power.toString() : "---");
diff --git a/src/ui/party-exp-bar.ts b/src/ui/party-exp-bar.ts
index 506b8b5c825..d2521225375 100644
--- a/src/ui/party-exp-bar.ts
+++ b/src/ui/party-exp-bar.ts
@@ -7,7 +7,7 @@ export default class PartyExpBar extends Phaser.GameObjects.Container {
   private pokemonIcon: Phaser.GameObjects.Container;
   private expText: Phaser.GameObjects.Text;
 
-  private tween: Phaser.Tweens.Tween;
+  private tween: Phaser.Tweens.Tween | null;
 
   public shown: boolean;
 
@@ -16,7 +16,7 @@ export default class PartyExpBar extends Phaser.GameObjects.Container {
   }
 
   setup(): void {
-    this.bg = this.scene.add.nineslice(0, 0, "party_exp_bar", null, 8, 18, 21, 5, 6, 4);
+    this.bg = this.scene.add.nineslice(0, 0, "party_exp_bar", undefined, 8, 18, 21, 5, 6, 4);
     this.bg.setOrigin(0, 0);
 
     this.add(this.bg);
diff --git a/src/ui/party-ui-handler.ts b/src/ui/party-ui-handler.ts
index 7b77b71f4ec..3a9b3463ef1 100644
--- a/src/ui/party-ui-handler.ts
+++ b/src/ui/party-ui-handler.ts
@@ -118,9 +118,9 @@ export enum PartyOption {
 export type PartySelectCallback = (cursor: integer, option: PartyOption) => void;
 export type PartyModifierTransferSelectCallback = (fromCursor: integer, index: integer, itemQuantity?: integer, toCursor?: integer) => void;
 export type PartyModifierSpliceSelectCallback = (fromCursor: integer, toCursor?: integer) => void;
-export type PokemonSelectFilter = (pokemon: PlayerPokemon) => string;
-export type PokemonModifierTransferSelectFilter = (pokemon: PlayerPokemon, modifier: PokemonHeldItemModifier) => string;
-export type PokemonMoveSelectFilter = (pokemonMove: PokemonMove) => string;
+export type PokemonSelectFilter = (pokemon: PlayerPokemon) => string | null;
+export type PokemonModifierTransferSelectFilter = (pokemon: PlayerPokemon, modifier: PokemonHeldItemModifier) => string | null;
+export type PokemonMoveSelectFilter = (pokemonMove: PokemonMove) => string | null;
 
 export default class PartyUiHandler extends MessageUiHandler {
   private partyUiMode: PartyUiMode;
@@ -142,7 +142,7 @@ export default class PartyUiHandler extends MessageUiHandler {
   /** This is only public for test/ui/transfer-item.test.ts */
   public optionsContainer: Phaser.GameObjects.Container;
   private optionsBg: Phaser.GameObjects.NineSlice;
-  private optionsCursorObj: Phaser.GameObjects.Image;
+  private optionsCursorObj: Phaser.GameObjects.Image | null;
   private options: integer[];
 
   private transferMode: boolean;
@@ -156,7 +156,7 @@ export default class PartyUiHandler extends MessageUiHandler {
   private transferAll: boolean;
 
   private lastCursor: integer = 0;
-  private selectCallback: PartySelectCallback | PartyModifierTransferSelectCallback;
+  private selectCallback: PartySelectCallback | PartyModifierTransferSelectCallback | null;
   private selectFilter: PokemonSelectFilter | PokemonModifierTransferSelectFilter;
   private moveSelectFilter: PokemonMoveSelectFilter;
   private tmMoveId: Moves;
@@ -377,17 +377,17 @@ export default class PartyUiHandler extends MessageUiHandler {
           this.moveInfoOverlay.clear();
           const filterResult = (this.selectFilter as PokemonSelectFilter)(pokemon);
           if (filterResult === null) {
-            this.selectCallback(this.cursor, option);
+            this.selectCallback?.(this.cursor, option);
             this.clearOptions();
           } else {
             this.clearOptions();
-            this.showText(filterResult as string, null, () => this.showText(null, 0), null, true);
+            this.showText(filterResult as string, undefined, () => this.showText(null, 0), undefined, true);
           }
           ui.playSelect();
           return true;
         } else if ((option !== PartyOption.SUMMARY && option !== PartyOption.UNPAUSE_EVOLUTION && option !== PartyOption.UNSPLICE && option !== PartyOption.RELEASE && option !== PartyOption.CANCEL && option !== PartyOption.RENAME)
           || (option === PartyOption.RELEASE && this.partyUiMode === PartyUiMode.RELEASE)) {
-          let filterResult: string;
+          let filterResult: string | null;
           const getTransferrableItemsFromPokemon = (pokemon: PlayerPokemon) =>
             this.scene.findModifiers(m => m instanceof PokemonHeldItemModifier && m.isTransferrable && m.pokemonId === pokemon.id) as PokemonHeldItemModifier[];
           if (option !== PartyOption.TRANSFER && option !== PartyOption.SPLICE) {
@@ -396,7 +396,7 @@ export default class PartyUiHandler extends MessageUiHandler {
               filterResult = this.FilterChallengeLegal(pokemon);
             }
             if (filterResult === null && this.partyUiMode === PartyUiMode.MOVE_MODIFIER) {
-              filterResult = this.moveSelectFilter(pokemon.moveset[this.optionsCursor]);
+              filterResult = this.moveSelectFilter(pokemon.moveset[this.optionsCursor]!); // TODO: is this bang correct?
             }
           } else {
             filterResult = (this.selectFilter as PokemonModifierTransferSelectFilter)(pokemon, getTransferrableItemsFromPokemon(this.scene.getParty()[this.transferCursor])[this.transferOptionCursor]);
@@ -451,7 +451,7 @@ export default class PartyUiHandler extends MessageUiHandler {
             return true;
           } else {
             this.clearOptions();
-            this.showText(filterResult as string, null, () => this.showText(null, 0), null, true);
+            this.showText(filterResult as string, undefined, () => this.showText(null, 0), undefined, true);
           }
         } else if (option === PartyOption.SUMMARY) {
           ui.playSelect();
@@ -461,18 +461,18 @@ export default class PartyUiHandler extends MessageUiHandler {
           this.clearOptions();
           ui.playSelect();
           pokemon.pauseEvolutions = false;
-          this.showText(i18next.t("partyUiHandler:unpausedEvolutions", { pokemonName: getPokemonNameWithAffix(pokemon) }), null, () => this.showText(null, 0), null, true);
+          this.showText(i18next.t("partyUiHandler:unpausedEvolutions", { pokemonName: getPokemonNameWithAffix(pokemon) }), undefined, () => this.showText(null, 0), null, true);
         } else if (option === PartyOption.UNSPLICE) {
           this.clearOptions();
           ui.playSelect();
-          this.showText(i18next.t("partyUiHandler:unspliceConfirmation", { fusionName: pokemon.fusionSpecies.name, pokemonName: pokemon.name }), null, () => {
+          this.showText(i18next.t("partyUiHandler:unspliceConfirmation", { fusionName: pokemon.fusionSpecies?.name, pokemonName: pokemon.name }), null, () => {
             ui.setModeWithoutClear(Mode.CONFIRM, () => {
               const fusionName = pokemon.name;
               pokemon.unfuse().then(() => {
                 this.clearPartySlots();
                 this.populatePartySlots();
                 ui.setMode(Mode.PARTY);
-                this.showText(i18next.t("partyUiHandler:wasReverted", { fusionName: fusionName, pokemonName: pokemon.name }), null, () => {
+                this.showText(i18next.t("partyUiHandler:wasReverted", { fusionName: fusionName, pokemonName: pokemon.name }), undefined, () => {
                   ui.setMode(Mode.PARTY);
                   this.showText(null, 0);
                 }, null, true);
@@ -732,7 +732,7 @@ export default class PartyUiHandler extends MessageUiHandler {
     return changed;
   }
 
-  showText(text: string, delay?: integer, callback?: Function, callbackDelay?: integer, prompt?: boolean, promptDelay?: integer) {
+  showText(text: string | null, delay?: integer | null, callback?: Function | null, callbackDelay?: integer | null, prompt?: boolean, promptDelay?: integer) {
     if (text === null) {
       text = defaultMessage;
     }
@@ -792,7 +792,7 @@ export default class PartyUiHandler extends MessageUiHandler {
 
     const learnableLevelMoves = this.partyUiMode === PartyUiMode.REMEMBER_MOVE_MODIFIER
       ? pokemon.getLearnableLevelMoves()
-      : null;
+      : [];
 
     if (this.partyUiMode === PartyUiMode.REMEMBER_MOVE_MODIFIER && learnableLevelMoves?.length) {
       // show the move overlay with info for the first move
@@ -802,7 +802,7 @@ export default class PartyUiHandler extends MessageUiHandler {
     const itemModifiers = this.partyUiMode === PartyUiMode.MODIFIER_TRANSFER
       ? this.scene.findModifiers(m => m instanceof PokemonHeldItemModifier
         && m.isTransferrable && m.pokemonId === pokemon.id) as PokemonHeldItemModifier[]
-      : null;
+      : [];
 
     if (this.options.length) {
       this.options.splice(0, this.options.length);
@@ -810,7 +810,7 @@ export default class PartyUiHandler extends MessageUiHandler {
       this.eraseOptionsCursor();
     }
 
-    let formChangeItemModifiers: PokemonFormChangeItemModifier[];
+    let formChangeItemModifiers: PokemonFormChangeItemModifier[] | undefined;
 
     if (this.partyUiMode !== PartyUiMode.MOVE_MODIFIER && this.partyUiMode !== PartyUiMode.REMEMBER_MOVE_MODIFIER && (this.transferMode || this.partyUiMode !== PartyUiMode.MODIFIER_TRANSFER)) {
       switch (this.partyUiMode) {
@@ -951,7 +951,7 @@ export default class PartyUiHandler extends MessageUiHandler {
         case PartyOption.MOVE_2:
         case PartyOption.MOVE_3:
         case PartyOption.MOVE_4:
-          const move = pokemon.moveset[option - PartyOption.MOVE_1];
+          const move = pokemon.moveset[option - PartyOption.MOVE_1]!; // TODO: is the bang correct?
           if (this.showMovePp) {
             const maxPP = move.getMovePp();
             const currPP = maxPP - move.ppUsed;
@@ -1060,7 +1060,7 @@ export default class PartyUiHandler extends MessageUiHandler {
       if (this.partyUiMode === PartyUiMode.RELEASE) {
         const selectCallback = this.selectCallback;
         this.selectCallback = null;
-        selectCallback(this.cursor, PartyOption.RELEASE);
+        selectCallback && selectCallback(this.cursor, PartyOption.RELEASE);
       }
       this.showText(null, 0);
     }, null, true);
diff --git a/src/ui/pokeball-tray.ts b/src/ui/pokeball-tray.ts
index 00a8cdadc97..cf3b24c4d11 100644
--- a/src/ui/pokeball-tray.ts
+++ b/src/ui/pokeball-tray.ts
@@ -15,7 +15,7 @@ export default class PokeballTray extends Phaser.GameObjects.Container {
   }
 
   setup(): void {
-    this.bg = this.scene.add.nineslice(0, 0, `pb_tray_overlay_${this.player ? "player" : "enemy"}`, null, 104, 4, 48, 8, 0, 0);
+    this.bg = this.scene.add.nineslice(0, 0, `pb_tray_overlay_${this.player ? "player" : "enemy"}`, undefined, 104, 4, 48, 8, 0, 0);
     this.bg.setOrigin(this.player ? 1 : 0, 0);
 
     this.add(this.bg);
diff --git a/src/ui/pokemon-icon-anim-handler.ts b/src/ui/pokemon-icon-anim-handler.ts
index 99fe39c4184..d6796d5cb5d 100644
--- a/src/ui/pokemon-icon-anim-handler.ts
+++ b/src/ui/pokemon-icon-anim-handler.ts
@@ -21,7 +21,9 @@ export default class PokemonIconAnimHandler {
       const value = tween.getValue();
       this.toggled = !!value;
       for (const i of this.icons.keys()) {
-        i.y += this.getModeYDelta(this.icons.get(i)) * (this.toggled ? 1 : -1);
+        const icon = this.icons.get(i);
+        const delta = icon ? this.getModeYDelta(icon) : 0;
+        i.y += delta * (this.toggled ? 1 : -1);
       }
     };
     scene.tweens.addCounter({
@@ -56,7 +58,7 @@ export default class PokemonIconAnimHandler {
       }
       if (this.toggled) {
         const lastYDelta = this.icons.has(i)
-          ? this.icons.get(i)
+          ? this.icons.get(i)!
           : 0;
         const yDelta = this.getModeYDelta(mode);
         i.y += yDelta + lastYDelta;
@@ -71,7 +73,9 @@ export default class PokemonIconAnimHandler {
     }
     for (const i of icons) {
       if (this.toggled) {
-        i.y -= this.getModeYDelta(this.icons.get(i));
+        const icon = this.icons.get(i);
+        const delta = icon ? this.getModeYDelta(icon) : 0;
+        i.y -= delta;
       }
       this.icons.delete(i);
     }
@@ -80,7 +84,9 @@ export default class PokemonIconAnimHandler {
   removeAll(): void {
     for (const i of this.icons.keys()) {
       if (this.toggled) {
-        i.y -= this.getModeYDelta(this.icons.get(i));
+        const icon = this.icons.get(i);
+        const delta = icon ? this.getModeYDelta(icon) : 0;
+        i.y -= delta;
       }
       this.icons.delete(i);
     }
diff --git a/src/ui/pokemon-info-container.ts b/src/ui/pokemon-info-container.ts
index b2ee5a9164a..edb85ecff7a 100644
--- a/src/ui/pokemon-info-container.ts
+++ b/src/ui/pokemon-info-container.ts
@@ -80,8 +80,8 @@ export default class PokemonInfoContainer extends Phaser.GameObjects.Container {
 
   setup(): void {
     this.setName("pkmn-info");
-    const currentLanguage = i18next.resolvedLanguage;
-    const langSettingKey = Object.keys(languageSettings).find(lang => currentLanguage.includes(lang));
+    const currentLanguage = i18next.resolvedLanguage!; // TODO: is this bang correct?
+    const langSettingKey = Object.keys(languageSettings).find(lang => currentLanguage?.includes(lang))!; // TODO: is this bang correct?
     const textSettings = languageSettings[langSettingKey];
     const infoBg = addWindow(this.scene, 0, 0, this.infoWindowWidth, 132);
     infoBg.setOrigin(0.5, 0.5);
@@ -243,7 +243,7 @@ export default class PokemonInfoContainer extends Phaser.GameObjects.Container {
         this.pokemonFormText.setText(formName.length > this.numCharsBeforeCutoff ? formName.substring(0, this.numCharsBeforeCutoff - 3) + "..." : formName);
         if (formName.length > this.numCharsBeforeCutoff) {
           this.pokemonFormText.setInteractive(new Phaser.Geom.Rectangle(0, 0, this.pokemonFormText.width, this.pokemonFormText.height), Phaser.Geom.Rectangle.Contains);
-          this.pokemonFormText.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip(null, pokemon.species.forms?.[pokemon.formIndex]?.formName, true));
+          this.pokemonFormText.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip("", pokemon.species.forms?.[pokemon.formIndex]?.formName, true));
           this.pokemonFormText.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
         } else {
           this.pokemonFormText.disableInteractive();
@@ -302,7 +302,7 @@ export default class PokemonInfoContainer extends Phaser.GameObjects.Container {
         const shinyDescriptor = doubleShiny || baseVariant ?
           `${baseVariant === 2 ? i18next.t("common:epicShiny") : baseVariant === 1 ? i18next.t("common:rareShiny") : i18next.t("common:commonShiny")}${doubleShiny ? `/${pokemon.fusionVariant === 2 ? i18next.t("common:epicShiny") : pokemon.fusionVariant === 1 ? i18next.t("common:rareShiny") : i18next.t("common:commonShiny")}` : ""}`
           : "";
-        this.pokemonShinyIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip(null, `${i18next.t("common:shinyOnHover")}${shinyDescriptor ? ` (${shinyDescriptor})` : ""}`, true));
+        this.pokemonShinyIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip("", `${i18next.t("common:shinyOnHover")}${shinyDescriptor ? ` (${shinyDescriptor})` : ""}`, true));
         this.pokemonShinyIcon.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
 
         const newShiny = BigInt(1 << (pokemon.shiny ? 1 : 0));
@@ -324,11 +324,11 @@ export default class PokemonInfoContainer extends Phaser.GameObjects.Container {
       }
 
       const starterSpeciesId = pokemon.species.getRootSpeciesId();
-      const originalIvs: integer[] = this.scene.gameData.dexData[starterSpeciesId].caughtAttr
+      const originalIvs: integer[] | null = this.scene.gameData.dexData[starterSpeciesId].caughtAttr
         ? this.scene.gameData.dexData[starterSpeciesId].ivs
         : null;
 
-      this.statsContainer.updateIvs(pokemon.ivs, originalIvs);
+      this.statsContainer.updateIvs(pokemon.ivs, originalIvs!); // TODO: is this bang correct?
 
       this.scene.tweens.add({
         targets: this,
@@ -352,7 +352,7 @@ export default class PokemonInfoContainer extends Phaser.GameObjects.Container {
       }
 
       for (let m = 0; m < 4; m++) {
-        const move = m < pokemon.moveset.length ? pokemon.moveset[m].getMove() : null;
+        const move = m < pokemon.moveset.length && pokemon.moveset[m] ? pokemon.moveset[m]!.getMove() : null;
         this.pokemonMoveBgs[m].setFrame(Type[move ? move.type : Type.UNKNOWN].toString().toLowerCase());
         this.pokemonMoveLabels[m].setText(move ? move.name : "-");
         this.pokemonMovesContainers[m].setVisible(!!move);
diff --git a/src/ui/registration-form-ui-handler.ts b/src/ui/registration-form-ui-handler.ts
index d5e7f239378..733aab79b05 100644
--- a/src/ui/registration-form-ui-handler.ts
+++ b/src/ui/registration-form-ui-handler.ts
@@ -92,7 +92,7 @@ export default class RegistrationFormUiHandler extends FormModalUiHandler {
                 .then(response => {
                   if (response.hasOwnProperty("token")) {
                     Utils.setCookie(Utils.sessionIdKey, response.token);
-                    originalRegistrationAction();
+                    originalRegistrationAction && originalRegistrationAction();
                   } else {
                     onFail(response);
                   }
diff --git a/src/ui/save-slot-select-ui-handler.ts b/src/ui/save-slot-select-ui-handler.ts
index 8a81ac4858d..e6ab0d3b3c3 100644
--- a/src/ui/save-slot-select-ui-handler.ts
+++ b/src/ui/save-slot-select-ui-handler.ts
@@ -29,11 +29,11 @@ export default class SaveSlotSelectUiHandler extends MessageUiHandler {
   private sessionSlots: SessionSlot[];
 
   private uiMode: SaveSlotUiMode;
-  private saveSlotSelectCallback: SaveSlotSelectCallback;
+  private saveSlotSelectCallback: SaveSlotSelectCallback | null;
 
   private scrollCursor: integer = 0;
 
-  private cursorObj: Phaser.GameObjects.NineSlice;
+  private cursorObj: Phaser.GameObjects.NineSlice | null;
 
   private sessionSlotsContainerInitialY: number;
 
@@ -106,16 +106,16 @@ export default class SaveSlotSelectUiHandler extends MessageUiHandler {
           switch (this.uiMode) {
           case SaveSlotUiMode.LOAD:
             this.saveSlotSelectCallback = null;
-            originalCallback(cursor);
+            originalCallback && originalCallback(cursor);
             break;
           case SaveSlotUiMode.SAVE:
             const saveAndCallback = () => {
               const originalCallback = this.saveSlotSelectCallback;
               this.saveSlotSelectCallback = null;
               ui.revertMode();
-              ui.showText(null, 0);
+              ui.showText("", 0);
               ui.setMode(Mode.MESSAGE);
-              originalCallback(cursor);
+              originalCallback && originalCallback(cursor);
             };
             if (this.sessionSlots[cursor].hasData) {
               ui.showText(i18next.t("saveSlotSelectUiHandler:overwriteData"), null, () => {
@@ -129,7 +129,7 @@ export default class SaveSlotSelectUiHandler extends MessageUiHandler {
                   });
                 }, () => {
                   ui.revertMode();
-                  ui.showText(null, 0);
+                  ui.showText("", 0);
                 }, false, 0, 19, 2000);
               });
             } else if (this.sessionSlots[cursor].hasData === false) {
@@ -143,7 +143,7 @@ export default class SaveSlotSelectUiHandler extends MessageUiHandler {
         }
       } else {
         this.saveSlotSelectCallback = null;
-        originalCallback(-1);
+        originalCallback && originalCallback(-1);
         success = true;
       }
     } else {
@@ -202,7 +202,7 @@ export default class SaveSlotSelectUiHandler extends MessageUiHandler {
     const changed = super.setCursor(cursor);
 
     if (!this.cursorObj) {
-      this.cursorObj = this.scene.add.nineslice(0, 0, "select_cursor_highlight_thick", null, 296, 44, 6, 6, 6, 6);
+      this.cursorObj = this.scene.add.nineslice(0, 0, "select_cursor_highlight_thick", undefined, 296, 44, 6, 6, 6, 6);
       this.cursorObj.setOrigin(0, 0);
       this.sessionSlotsContainer.add(this.cursorObj);
     }
@@ -292,7 +292,7 @@ class SessionSlot extends Phaser.GameObjects.Container {
       const icon = this.scene.addPokemonIcon(pokemon, 0, 0, 0, 0);
 
       const text = addTextObject(this.scene, 32, 20, `${i18next.t("saveSlotSelectUiHandler:lv")}${Utils.formatLargeNumber(pokemon.level, 1000)}`, TextStyle.PARTY, { fontSize: "54px", color: "#f8f8f8" });
-      text.setShadow(0, 0, null);
+      text.setShadow(0, 0, undefined);
       text.setStroke("#424242", 14);
       text.setOrigin(1, 0);
 
@@ -316,9 +316,11 @@ class SessionSlot extends Phaser.GameObjects.Container {
       if (modifier instanceof PokemonHeldItemModifier) {
         continue;
       }
-      const icon = modifier.getIcon(this.scene, false);
-      icon.setPosition(24 * visibleModifierIndex, 0);
-      modifierIconsContainer.add(icon);
+      const icon = modifier?.getIcon(this.scene, false);
+      if (icon) {
+        icon.setPosition(24 * visibleModifierIndex, 0);
+        modifierIconsContainer.add(icon);
+      }
       if (++visibleModifierIndex === 12) {
         break;
       }
diff --git a/src/ui/settings/abstract-binding-ui-handler.ts b/src/ui/settings/abstract-binding-ui-handler.ts
index 809c4ffa2f8..3da555e2c96 100644
--- a/src/ui/settings/abstract-binding-ui-handler.ts
+++ b/src/ui/settings/abstract-binding-ui-handler.ts
@@ -7,6 +7,8 @@ import {Button} from "#enums/buttons";
 import {NavigationManager} from "#app/ui/settings/navigationMenu";
 import i18next from "i18next";
 
+type CancelFn = (succes?: boolean) => boolean;
+
 /**
  * Abstract class for handling UI elements related to button bindings.
  */
@@ -35,7 +37,7 @@ export default abstract class AbstractBindingUiHandler extends UiHandler {
   protected targetButtonIcon: Phaser.GameObjects.Sprite;
 
   // Function to call on cancel or completion of binding.
-  protected cancelFn: (boolean?) => boolean;
+  protected cancelFn: CancelFn | null;
   abstract swapAction(): boolean;
 
   protected timeLeftAutoClose: number = 5;
@@ -51,7 +53,7 @@ export default abstract class AbstractBindingUiHandler extends UiHandler {
      * @param mode - The UI mode.
      */
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
   }
 
   /**
@@ -107,7 +109,7 @@ export default abstract class AbstractBindingUiHandler extends UiHandler {
       if (this.timeLeftAutoClose >= 0) {
         this.manageAutoCloseTimer();
       } else {
-        this.cancelFn();
+        this.cancelFn && this.cancelFn();
       }
     }, 1000);
   }
@@ -163,7 +165,7 @@ export default abstract class AbstractBindingUiHandler extends UiHandler {
      */
   processInput(button: Button): boolean {
     if (this.buttonPressed === null) {
-      return;
+      return false; // TODO: is false correct as default? (previously was `undefined`)
     }
     const ui = this.getUi();
     let success = false;
@@ -177,11 +179,11 @@ export default abstract class AbstractBindingUiHandler extends UiHandler {
     case Button.ACTION:
       // Process actions based on current cursor position.
       if (this.cursor === 0) {
-        this.cancelFn();
+        this.cancelFn && this.cancelFn();
       } else {
         success = this.swapAction();
         NavigationManager.getInstance().updateIcons();
-        this.cancelFn(success);
+        this.cancelFn && this.cancelFn(success);
       }
       break;
     }
@@ -242,7 +244,7 @@ export default abstract class AbstractBindingUiHandler extends UiHandler {
      * @param assignedButtonIcon - The icon of the button that is assigned.
      * @param type - The type of button press.
      */
-  onInputDown(buttonIcon: string, assignedButtonIcon: string, type: string): void {
+  onInputDown(buttonIcon: string, assignedButtonIcon: string | null, type: string): void {
     clearTimeout(this.countdownTimer);
     this.timerText.setText("");
     this.newButtonIcon.setTexture(type);
diff --git a/src/ui/settings/abstract-control-settings-ui-handler.ts b/src/ui/settings/abstract-control-settings-ui-handler.ts
index 9bf0cb40975..1f0c2b98fbd 100644
--- a/src/ui/settings/abstract-control-settings-ui-handler.ts
+++ b/src/ui/settings/abstract-control-settings-ui-handler.ts
@@ -33,7 +33,7 @@ export default abstract class AbstractControlSettingsUiHandler extends UiHandler
 
   protected scrollCursor: integer;
   protected optionCursors: integer[];
-  protected cursorObj: Phaser.GameObjects.NineSlice;
+  protected cursorObj: Phaser.GameObjects.NineSlice | null;
 
   protected optionsBg: Phaser.GameObjects.NineSlice;
   protected actionsBg: Phaser.GameObjects.NineSlice;
@@ -74,13 +74,13 @@ export default abstract class AbstractControlSettingsUiHandler extends UiHandler
    * @param mode - The UI mode.
    */
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
     this.rowsToDisplay = 8;
   }
 
   getLocalStorageSetting(): object {
     // Retrieve the settings from local storage or use an empty object if none exist.
-    const settings: object = localStorage.hasOwnProperty(this.localStoragePropertyName) ? JSON.parse(localStorage.getItem(this.localStoragePropertyName)) : {};
+    const settings: object = localStorage.hasOwnProperty(this.localStoragePropertyName) ? JSON.parse(localStorage.getItem(this.localStoragePropertyName)!) : {}; // TODO: is this bang correct?
     return settings;
   }
 
@@ -442,7 +442,7 @@ export default abstract class AbstractControlSettingsUiHandler extends UiHandler
       switch (button) {
       case Button.ACTION:
         if (!this.optionCursors || !this.optionValueLabels) {
-          return;
+          return false; // TODO: is false correct as default? (previously was `undefined`)
         }
         if (this.settingBlacklisted.includes(setting) || !setting.includes("BUTTON_")) {
           success = false;
@@ -490,7 +490,7 @@ export default abstract class AbstractControlSettingsUiHandler extends UiHandler
         break;
       case Button.LEFT: // Move selection left within the current option set.
         if (!this.optionCursors || !this.optionValueLabels) {
-          return;
+          return false; // TODO: is false correct as default? (previously was `undefined`)
         }
         if (this.settingBlacklisted.includes(setting) || setting.includes("BUTTON_")) {
           success = false;
@@ -500,7 +500,7 @@ export default abstract class AbstractControlSettingsUiHandler extends UiHandler
         break;
       case Button.RIGHT: // Move selection right within the current option set.
         if (!this.optionCursors || !this.optionValueLabels) {
-          return;
+          return false; // TODO: is false correct as default? (previously was `undefined`)
         }
         if (this.settingBlacklisted.includes(setting) || setting.includes("BUTTON_")) {
           success = false;
@@ -526,7 +526,7 @@ export default abstract class AbstractControlSettingsUiHandler extends UiHandler
   resetScroll() {
     this.cursorObj?.destroy();
     this.cursorObj = null;
-    this.cursor = null;
+    this.cursor = 0;
     this.setCursor(0);
     this.setScrollCursor(0);
     this.updateSettingsScroll();
@@ -547,7 +547,7 @@ export default abstract class AbstractControlSettingsUiHandler extends UiHandler
 
     // Check if the cursor object exists, if not, create it.
     if (!this.cursorObj) {
-      this.cursorObj = this.scene.add.nineslice(0, 0, "summary_moves_cursor", null, (this.scene.game.canvas.width / 6) - 10, 16, 1, 1, 1, 1);
+      this.cursorObj = this.scene.add.nineslice(0, 0, "summary_moves_cursor", undefined, (this.scene.game.canvas.width / 6) - 10, 16, 1, 1, 1, 1);
       this.cursorObj.setOrigin(0, 0); // Set the origin to the top-left corner.
       this.optionsContainer.add(this.cursorObj); // Add the cursor to the options container.
     }
diff --git a/src/ui/settings/abstract-settings-ui-handler.ts b/src/ui/settings/abstract-settings-ui-handler.ts
index 4747a17be32..96d8e790c8a 100644
--- a/src/ui/settings/abstract-settings-ui-handler.ts
+++ b/src/ui/settings/abstract-settings-ui-handler.ts
@@ -30,7 +30,7 @@ export default class AbstractSettingsUiHandler extends UiHandler {
 
   protected navigationIcons: InputsIcons;
 
-  private cursorObj: Phaser.GameObjects.NineSlice;
+  private cursorObj: Phaser.GameObjects.NineSlice | null;
 
   private reloadSettings: Array<Setting>;
   private reloadRequired: boolean;
@@ -41,7 +41,7 @@ export default class AbstractSettingsUiHandler extends UiHandler {
   protected localStorageKey: string;
 
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
 
     this.reloadRequired = false;
     this.rowsToDisplay = 8;
@@ -180,7 +180,7 @@ export default class AbstractSettingsUiHandler extends UiHandler {
     super.show(args);
     this.updateBindings();
 
-    const settings: object = localStorage.hasOwnProperty(this.localStorageKey) ? JSON.parse(localStorage.getItem(this.localStorageKey)) : {};
+    const settings: object = localStorage.hasOwnProperty(this.localStorageKey) ? JSON.parse(localStorage.getItem(this.localStorageKey)!) : {}; // TODO: is this bang correct?
 
     this.settings.forEach((setting, s) => this.setOptionCursor(s, settings.hasOwnProperty(setting.key) ? settings[setting.key] : this.settings[s].default));
 
@@ -285,7 +285,7 @@ export default class AbstractSettingsUiHandler extends UiHandler {
     const ret = super.setCursor(cursor);
 
     if (!this.cursorObj) {
-      this.cursorObj = this.scene.add.nineslice(0, 0, "summary_moves_cursor", null, (this.scene.game.canvas.width / 6) - 10, 16, 1, 1, 1, 1);
+      this.cursorObj = this.scene.add.nineslice(0, 0, "summary_moves_cursor", undefined, (this.scene.game.canvas.width / 6) - 10, 16, 1, 1, 1, 1);
       this.cursorObj.setOrigin(0, 0);
       this.optionsContainer.add(this.cursorObj);
     }
diff --git a/src/ui/settings/gamepad-binding-ui-handler.ts b/src/ui/settings/gamepad-binding-ui-handler.ts
index 70291da15a2..16a8b9d2c30 100644
--- a/src/ui/settings/gamepad-binding-ui-handler.ts
+++ b/src/ui/settings/gamepad-binding-ui-handler.ts
@@ -10,7 +10,7 @@ export default class GamepadBindingUiHandler extends AbstractBindingUiHandler {
 
   constructor(scene: BattleScene, mode?: Mode) {
     super(scene, mode);
-    this.scene.input.gamepad.on("down", this.gamepadButtonDown, this);
+    this.scene.input.gamepad?.on("down", this.gamepadButtonDown, this);
   }
   setup() {
     super.setup();
diff --git a/src/ui/settings/keyboard-binding-ui-handler.ts b/src/ui/settings/keyboard-binding-ui-handler.ts
index 2a92bb0fa6c..0bc74da86ce 100644
--- a/src/ui/settings/keyboard-binding-ui-handler.ts
+++ b/src/ui/settings/keyboard-binding-ui-handler.ts
@@ -11,7 +11,7 @@ export default class KeyboardBindingUiHandler extends AbstractBindingUiHandler {
   constructor(scene: BattleScene, mode?: Mode) {
     super(scene, mode);
     // Listen to gamepad button down events to initiate binding.
-    scene.input.keyboard.on("keydown", this.onKeyDown, this);
+    scene.input.keyboard?.on("keydown", this.onKeyDown, this);
   }
   setup() {
     super.setup();
diff --git a/src/ui/settings/settings-keyboard-ui-handler.ts b/src/ui/settings/settings-keyboard-ui-handler.ts
index 5c4444991ad..3408359f33b 100644
--- a/src/ui/settings/settings-keyboard-ui-handler.ts
+++ b/src/ui/settings/settings-keyboard-ui-handler.ts
@@ -42,10 +42,10 @@ export default class SettingsKeyboardUiHandler extends AbstractControlSettingsUi
     this.settingBlacklisted = settingKeyboardBlackList;
     this.device = Device.KEYBOARD;
 
-    const deleteEvent = scene.input.keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.DELETE);
-    const restoreDefaultEvent = scene.input.keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.HOME);
-    deleteEvent.on("up", this.onDeleteDown, this);
-    restoreDefaultEvent.on("up", this.onHomeDown, this);
+    const deleteEvent = scene.input.keyboard?.addKey(Phaser.Input.Keyboard.KeyCodes.DELETE);
+    const restoreDefaultEvent = scene.input.keyboard?.addKey(Phaser.Input.Keyboard.KeyCodes.HOME);
+    deleteEvent && deleteEvent.on("up", this.onDeleteDown, this);
+    restoreDefaultEvent && restoreDefaultEvent.on("up", this.onHomeDown, this);
   }
 
   setSetting = setSettingKeyboard;
diff --git a/src/ui/starter-select-ui-handler.ts b/src/ui/starter-select-ui-handler.ts
index 028786c85f0..447f5c95e46 100644
--- a/src/ui/starter-select-ui-handler.ts
+++ b/src/ui/starter-select-ui-handler.ts
@@ -286,7 +286,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
   private abilityCursor: number = -1;
   private natureCursor: number = -1;
   private filterBarCursor: integer = 0;
-  private starterMoveset: StarterMoveset;
+  private starterMoveset: StarterMoveset | null;
   private scrollCursor: number;
 
   private allSpecies: PokemonSpecies[] = [];
@@ -298,7 +298,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
   private starterAbilityIndexes: integer[] = [];
   private starterNatures: Nature[] = [];
   private starterMovesets: StarterMoveset[] = [];
-  private speciesStarterDexEntry: DexEntry;
+  private speciesStarterDexEntry: DexEntry | null;
   private speciesStarterMoves: Moves[];
   private canCycleShiny: boolean;
   private canCycleForm: boolean;
@@ -309,7 +309,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
   private value: integer = 0;
   private canAddParty: boolean;
 
-  private assetLoadCancelled: Utils.BooleanHolder;
+  private assetLoadCancelled: Utils.BooleanHolder | null;
   public cursorObj: Phaser.GameObjects.Image;
   private starterCursorObjs: Phaser.GameObjects.Image[];
   private pokerusCursorObjs: Phaser.GameObjects.Image[];
@@ -331,7 +331,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
   private instructionRowY = 0;
   private instructionRowTextOffset = 12;
 
-  private starterSelectCallback: StarterSelectCallback;
+  private starterSelectCallback: StarterSelectCallback | null;
 
   private starterPreferences: StarterPreferences;
 
@@ -343,8 +343,8 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
 
   setup() {
     const ui = this.getUi();
-    const currentLanguage = i18next.resolvedLanguage;
-    const langSettingKey = Object.keys(languageSettings).find(lang => currentLanguage.includes(lang));
+    const currentLanguage = i18next.resolvedLanguage!; // TODO: is this bang correct?
+    const langSettingKey = Object.keys(languageSettings).find(lang => currentLanguage.includes(lang))!; // TODO: is this bang correct?
     const textSettings = languageSettings[langSettingKey];
 
     this.starterSelectContainer = this.scene.add.container(0, -this.scene.game.canvas.height / 6);
@@ -574,7 +574,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
     startLabel.setOrigin(0.5, 0);
     this.starterSelectContainer.add(startLabel);
 
-    this.startCursorObj = this.scene.add.nineslice(teamWindowX+4, 160, "select_cursor", null, 26, 15, 6, 6, 6, 6);
+    this.startCursorObj = this.scene.add.nineslice(teamWindowX+4, 160, "select_cursor", undefined, 26, 15, 6, 6, 6, 6);
     this.startCursorObj.setVisible(false);
     this.startCursorObj.setOrigin(0, 0);
     this.starterSelectContainer.add(this.startCursorObj);
@@ -845,7 +845,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
     this.scene.executeWithSeedOffset(() => {
       for (let c = 0; c < 3; c++) {
         let randomSpeciesId: Species;
-        let species: PokemonSpecies;
+        let species: PokemonSpecies | undefined;
 
         const generateSpecies = () => {
           randomSpeciesId = Utils.randSeedItem(starterSpecies);
@@ -867,7 +867,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
           }
         } while (dupe);
 
-        this.pokerusSpecies.push(species);
+        this.pokerusSpecies.push(species!); // TODO: is the bang correct?
       }
     }, 0, date.getTime().toString());
 
@@ -1296,7 +1296,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
             species = this.starterSpecies[this.starterIconsCursorIndex];
           }
           const ui = this.getUi();
-          let options = [];
+          let options: any[] = []; // TODO: add proper type
 
           const [isDupe, removeIndex]: [boolean, number] = this.isInParty(species); // checks to see if the pokemon is a duplicate; if it is, returns the index that will be removed
 
@@ -1322,7 +1322,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
                     const cursorObj = this.starterCursorObjs[this.starterSpecies.length];
                     cursorObj.setVisible(true);
                     cursorObj.setPosition(this.cursorObj.x, this.cursorObj.y);
-                    this.addToParty(species, this.dexAttrCursor, this.abilityCursor, this.natureCursor as unknown as Nature, this.starterMoveset.slice(0) as StarterMoveset);
+                    this.addToParty(species, this.dexAttrCursor, this.abilityCursor, this.natureCursor as unknown as Nature, this.starterMoveset?.slice(0) as StarterMoveset);
                     ui.playSelect();
                   } else {
                     ui.playError(); // this should be redundant as there is now a trigger for when a pokemon can't be added to party
@@ -1378,7 +1378,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
                                     label: allMoves[sm].name,
                                     handler: () => {
                                       this.switchMoveHandler(i, sm, m);
-                                      showSwapOptions(this.starterMoveset);
+                                      showSwapOptions(this.starterMoveset!); // TODO: is this bang correct?
                                       return true;
                                     },
                                     onHover: () => {
@@ -1389,7 +1389,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
                                 }).concat({
                                   label: i18next.t("menu:cancel"),
                                   handler: () => {
-                                    showSwapOptions(this.starterMoveset);
+                                    showSwapOptions(this.starterMoveset!); // TODO: is this bang correct?
                                     return true;
                                   },
                                   onHover: () => {
@@ -1433,7 +1433,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
             options.push({
               label: i18next.t("starterSelectUiHandler:manageMoves"),
               handler: () => {
-                showSwapOptions(this.starterMoveset);
+                showSwapOptions(this.starterMoveset!); // TODO: is this bang correct?
                 return true;
               }
             });
@@ -1449,7 +1449,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
 
               ui.setMode(Mode.STARTER_SELECT).then(() => {
                 ui.showText(i18next.t("starterSelectUiHandler:selectNature"), null, () => {
-                  const natures = this.scene.gameData.getNaturesForAttr(this.speciesStarterDexEntry.natureAttr);
+                  const natures = this.scene.gameData.getNaturesForAttr(this.speciesStarterDexEntry?.natureAttr);
                   ui.setModeWithoutClear(Mode.OPTION_SELECT, {
                     options: natures.map((n: Nature, i: number) => {
                       const option: OptionSelectItem = {
@@ -1518,7 +1518,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
             }
           }
           const showUseCandies = () => { // this lets you use your candies
-            const options = [];
+            const options: any[] = []; // TODO: add proper type
             if (!(passiveAttr & PassiveAttr.UNLOCKED)) {
               const passiveCost = getPassiveCandyCount(speciesStarters[this.lastSpecies.speciesId]);
               options.push({
@@ -1691,7 +1691,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
             let newFormIndex = props.formIndex;
             do {
               newFormIndex = (newFormIndex + 1) % formCount;
-              if (this.lastSpecies.forms[newFormIndex].isStarterSelectable && this.speciesStarterDexEntry.caughtAttr & this.scene.gameData.getFormAttr(newFormIndex)) {
+              if (this.lastSpecies.forms[newFormIndex].isStarterSelectable && this.speciesStarterDexEntry!.caughtAttr! & this.scene.gameData.getFormAttr(newFormIndex)) { // TODO: are those bangs correct?
                 break;
               }
             } while (newFormIndex !== props.formIndex);
@@ -1736,7 +1736,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
           break;
         case Button.CYCLE_NATURE:
           if (this.canCycleNature) {
-            const natures = this.scene.gameData.getNaturesForAttr(this.speciesStarterDexEntry.natureAttr);
+            const natures = this.scene.gameData.getNaturesForAttr(this.speciesStarterDexEntry?.natureAttr);
             const natureIndex = natures.indexOf(this.natureCursor);
             const newNature = natures[natureIndex < natures.length - 1 ? natureIndex + 1 : 0];
             // store cycled nature as default
@@ -1751,24 +1751,24 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
             do {
               newVariant = (newVariant + 1) % 3;
               if (!newVariant) {
-                if (this.speciesStarterDexEntry.caughtAttr & DexAttr.DEFAULT_VARIANT) {
+                if (this.speciesStarterDexEntry!.caughtAttr & DexAttr.DEFAULT_VARIANT) { // TODO: is this bang correct?
                   break;
                 }
               } else if (newVariant === 1) {
-                if (this.speciesStarterDexEntry.caughtAttr & DexAttr.VARIANT_2) {
+                if (this.speciesStarterDexEntry!.caughtAttr & DexAttr.VARIANT_2) { // TODO: is this bang correct?
                   break;
                 }
               } else {
-                if (this.speciesStarterDexEntry.caughtAttr & DexAttr.VARIANT_3) {
+                if (this.speciesStarterDexEntry!.caughtAttr & DexAttr.VARIANT_3) { // TODO: is this bang correct?
                   break;
                 }
               }
             } while (newVariant !== props.variant);
             starterAttributes.variant = newVariant; // store the selected variant
-            this.setSpeciesDetails(this.lastSpecies, undefined, undefined, undefined, newVariant, undefined, undefined);
+            this.setSpeciesDetails(this.lastSpecies, undefined, undefined, undefined, newVariant as Variant, undefined, undefined);
             // Cycle tint based on current sprite tint
-            const tint = getVariantTint(newVariant);
-            this.pokemonShinyIcon.setFrame(getVariantIcon(newVariant));
+            const tint = getVariantTint(newVariant as Variant);
+            this.pokemonShinyIcon.setFrame(getVariantIcon(newVariant as Variant));
             this.pokemonShinyIcon.setTint(tint);
             success = true;
           }
@@ -1950,34 +1950,34 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
 
   switchMoveHandler(i: number, newMove: Moves, move: Moves) {
     const speciesId = this.lastSpecies.speciesId;
-    const existingMoveIndex = this.starterMoveset.indexOf(newMove);
-    this.starterMoveset[i] = newMove;
+    const existingMoveIndex = this.starterMoveset?.indexOf(newMove)!; // TODO: is this bang correct?
+    this.starterMoveset![i] = newMove; // TODO: is this bang correct?
     if (existingMoveIndex > -1) {
-      this.starterMoveset[existingMoveIndex] = move;
+      this.starterMoveset![existingMoveIndex] = move; // TODO: is this bang correct?
     }
     const props: DexAttrProps = this.scene.gameData.getSpeciesDexAttrProps(this.lastSpecies, this.dexAttrCursor);
     // species has different forms
     if (pokemonFormLevelMoves.hasOwnProperty(speciesId)) {
       // starterMoveData doesn't have base form moves or is using the single form format
       if (!this.scene.gameData.starterData[speciesId].moveset || Array.isArray(this.scene.gameData.starterData[speciesId].moveset)) {
-        this.scene.gameData.starterData[speciesId].moveset = { [props.formIndex]: this.starterMoveset.slice(0) as StarterMoveset };
+        this.scene.gameData.starterData[speciesId].moveset = { [props.formIndex]: this.starterMoveset?.slice(0) as StarterMoveset };
       }
       const starterMoveData = this.scene.gameData.starterData[speciesId].moveset;
 
       // starterMoveData doesn't have active form moves
       if (!starterMoveData.hasOwnProperty(props.formIndex)) {
-        this.scene.gameData.starterData[speciesId].moveset[props.formIndex] = this.starterMoveset.slice(0) as StarterMoveset;
+        this.scene.gameData.starterData[speciesId].moveset[props.formIndex] = this.starterMoveset?.slice(0) as StarterMoveset;
       }
 
       // does the species' starter move data have its form's starter moves and has it been updated
       if (starterMoveData.hasOwnProperty(props.formIndex)) {
         // active form move hasn't been updated
         if (starterMoveData[props.formIndex][existingMoveIndex] !== newMove) {
-          this.scene.gameData.starterData[speciesId].moveset[props.formIndex] = this.starterMoveset.slice(0) as StarterMoveset;
+          this.scene.gameData.starterData[speciesId].moveset[props.formIndex] = this.starterMoveset?.slice(0) as StarterMoveset;
         }
       }
     } else {
-      this.scene.gameData.starterData[speciesId].moveset = this.starterMoveset.slice(0) as StarterMoveset;
+      this.scene.gameData.starterData[speciesId].moveset = this.starterMoveset?.slice(0) as StarterMoveset;
     }
     this.setSpeciesDetails(this.lastSpecies, undefined, undefined, undefined, undefined, undefined, undefined, false);
 
@@ -1986,7 +1986,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
       Array.from({ length: this.starterSpecies.length }, (_, i) => {
         const starterSpecies = this.starterSpecies[i];
         if (starterSpecies.speciesId === speciesId) {
-          this.starterMovesets[i] = this.starterMoveset;
+          this.starterMovesets[i] = this.starterMoveset!; // TODO: is this bang correct?
         }
       });
     }
@@ -2382,22 +2382,22 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
     }
   }
 
-  setSpecies(species: PokemonSpecies) {
+  setSpecies(species: PokemonSpecies | null) {
     this.speciesStarterDexEntry = species ? this.scene.gameData.dexData[species.speciesId] : null;
     this.dexAttrCursor = species ? this.scene.gameData.getSpeciesDefaultDexAttr(species, false, true) : 0n;
     this.abilityCursor = species ? this.scene.gameData.getStarterSpeciesDefaultAbilityIndex(species) : 0;
     this.natureCursor = species ? this.scene.gameData.getSpeciesDefaultNature(species) : 0;
 
-    const starterAttributes : StarterAttributes = species ? {...this.starterPreferences[species.speciesId]} : null;
+    const starterAttributes : StarterAttributes | null = species ? {...this.starterPreferences[species.speciesId]} : null;
     // validate starterAttributes
     if (starterAttributes) {
       // this may cause changes so we created a copy of the attributes before
-      if (!isNaN(starterAttributes.variant)) {
+      if (starterAttributes.variant && !isNaN(starterAttributes.variant)) {
         if (![
-          this.speciesStarterDexEntry.caughtAttr & DexAttr.NON_SHINY,
-          this.speciesStarterDexEntry.caughtAttr & DexAttr.DEFAULT_VARIANT,
-          this.speciesStarterDexEntry.caughtAttr & DexAttr.VARIANT_2,
-          this.speciesStarterDexEntry.caughtAttr & DexAttr.VARIANT_3
+          this.speciesStarterDexEntry!.caughtAttr & DexAttr.NON_SHINY, // TODO: is that bang correct?
+          this.speciesStarterDexEntry!.caughtAttr & DexAttr.DEFAULT_VARIANT, // TODO: is that bang correct?
+          this.speciesStarterDexEntry!.caughtAttr & DexAttr.VARIANT_2, // TODO: is that bang correct?
+          this.speciesStarterDexEntry!.caughtAttr & DexAttr.VARIANT_3 // TODO: is that bang correct?
         ][starterAttributes.variant+1]) { // add 1 as -1 = non-shiny
           // requested variant wasn't unlocked, purging setting
           delete starterAttributes.variant;
@@ -2405,29 +2405,29 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
       }
 
       if (typeof starterAttributes.female !== "boolean" || !(starterAttributes.female ?
-        this.speciesStarterDexEntry.caughtAttr & DexAttr.FEMALE :
-        this.speciesStarterDexEntry.caughtAttr & DexAttr.MALE
+        this.speciesStarterDexEntry!.caughtAttr & DexAttr.FEMALE : // TODO: is this bang correct?
+        this.speciesStarterDexEntry!.caughtAttr & DexAttr.MALE // TODO: is this bang correct?
       )) {
         // requested gender wasn't unlocked, purging setting
         delete starterAttributes.female;
       }
 
-      const abilityAttr = this.scene.gameData.starterData[species.speciesId].abilityAttr;
+      const abilityAttr = this.scene.gameData.starterData[species!.speciesId].abilityAttr; // TODO: is this bang correct?
       if (![
         abilityAttr & AbilityAttr.ABILITY_1,
-        species.ability2 ? (abilityAttr & AbilityAttr.ABILITY_2) : abilityAttr & AbilityAttr.ABILITY_HIDDEN,
-        species.ability2 && abilityAttr & AbilityAttr.ABILITY_HIDDEN
-      ][starterAttributes.ability]) {
+        species!.ability2 ? (abilityAttr & AbilityAttr.ABILITY_2) : abilityAttr & AbilityAttr.ABILITY_HIDDEN, // TODO: is this bang correct?
+        species!.ability2 && abilityAttr & AbilityAttr.ABILITY_HIDDEN // TODO: is this bang correct?
+      ][starterAttributes.ability!]) { // TODO: is this bang correct?
         // requested ability wasn't unlocked, purging setting
         delete starterAttributes.ability;
       }
 
-      if (!(species.forms[starterAttributes.form]?.isStarterSelectable && this.speciesStarterDexEntry.caughtAttr & this.scene.gameData.getFormAttr(starterAttributes.form))) {
+      if (!(species?.forms[starterAttributes.form!]?.isStarterSelectable && this.speciesStarterDexEntry!.caughtAttr & this.scene.gameData.getFormAttr(starterAttributes.form!))) { // TODO: are those bangs correct?
         // requested form wasn't unlocked/isn't a starter form, purging setting
         delete starterAttributes.form;
       }
 
-      if (this.scene.gameData.getNaturesForAttr(this.speciesStarterDexEntry.natureAttr).indexOf(starterAttributes.nature as unknown as Nature) < 0) {
+      if (this.scene.gameData.getNaturesForAttr(this.speciesStarterDexEntry?.natureAttr).indexOf(starterAttributes.nature as unknown as Nature) < 0) {
         // requested nature wasn't unlocked, purging setting
         delete starterAttributes.nature;
       }
@@ -2437,7 +2437,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
       // load default nature from stater save data, if set
       this.natureCursor = starterAttributes.nature;
     }
-    if (!isNaN(starterAttributes?.ability)) {
+    if (starterAttributes?.ability && !isNaN(starterAttributes.ability)) {
       // load default nature from stater save data, if set
       this.abilityCursor = starterAttributes.ability;
     }
@@ -2448,7 +2448,8 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
         this.showStats();
       } else {
         this.statsContainer.setVisible(false);
-        this.statsContainer.updateIvs(null);
+        //@ts-ignore
+        this.statsContainer.updateIvs(null); // TODO: resolve ts-ignore. what. how? huh?
       }
     }
 
@@ -2465,7 +2466,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
       this.scene.tweens.getTweensOf(icon).forEach(tween => tween.resume());
     }
 
-    this.lastSpecies = species;
+    this.lastSpecies = species!; // TODO: is this bang correct?
 
     if (species && (this.speciesStarterDexEntry?.seenAttr || this.speciesStarterDexEntry?.caughtAttr)) {
       this.pokemonNumberText.setText(Utils.padInt(species.speciesId, 4));
@@ -2547,7 +2548,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
           const candyCropY = 16 - (16 * (currentFriendship / friendshipCap));
 
           if (this.pokemonCandyDarknessOverlay.visible) {
-            this.pokemonCandyDarknessOverlay.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip(null, `${currentFriendship}/${friendshipCap}`, true));
+            this.pokemonCandyDarknessOverlay.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip("", `${currentFriendship}/${friendshipCap}`, true));
             this.pokemonCandyDarknessOverlay.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
           }
 
@@ -2582,7 +2583,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
           // load default nature from stater save data, if set
           const defaultNature = starterAttributes?.nature || this.scene.gameData.getSpeciesDefaultNature(species);
           props = this.scene.gameData.getSpeciesDexAttrProps(species, defaultDexAttr);
-          if (!isNaN(starterAttributes?.variant)) {
+          if (starterAttributes?.variant && !isNaN(starterAttributes.variant)) {
             if (props.shiny = (starterAttributes.variant >= 0)) {
               props.variant = starterAttributes.variant as Variant;
             }
@@ -2594,7 +2595,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
         }
 
         const speciesForm = getPokemonSpeciesForm(species.speciesId, props.formIndex);
-        this.setTypeIcons(speciesForm.type1, speciesForm.type2);
+        this.setTypeIcons(speciesForm.type1, speciesForm!.type2!); // TODO: are those bangs correct?
 
         this.pokemonSprite.clearTint();
         if (this.pokerusSpecies.includes(species)) {
@@ -2648,14 +2649,14 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
       this.pokemonCandyCountText.setVisible(false);
       this.pokemonFormText.setVisible(false);
 
-      this.setSpeciesDetails(species, false, 0, false, 0, 0, 0);
+      this.setSpeciesDetails(species!, false, 0, false, 0, 0, 0); // TODO: is this bang correct?
       this.pokemonSprite.clearTint();
     }
   }
 
 
 
-  setSpeciesDetails(species: PokemonSpecies, shiny: boolean, formIndex: integer, female: boolean, variant: Variant, abilityIndex: integer, natureIndex: integer, forSeen: boolean = false): void {
+  setSpeciesDetails(species: PokemonSpecies, shiny?: boolean, formIndex?: integer, female?: boolean, variant?: Variant, abilityIndex?: integer, natureIndex?: integer, forSeen: boolean = false): void {
     const oldProps = species ? this.scene.gameData.getSpeciesDexAttrProps(species, this.dexAttrCursor) : null;
     const oldAbilityIndex = this.abilityCursor > -1 ? this.abilityCursor : this.scene.gameData.getStarterSpeciesDefaultAbilityIndex(species);
     const oldNatureIndex = this.natureCursor > -1 ? this.natureCursor : this.scene.gameData.getSpeciesDefaultNature(species);
@@ -2672,10 +2673,10 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
     }
 
     if (species) {
-      this.dexAttrCursor |= (shiny !== undefined ? !shiny : !(shiny = oldProps.shiny)) ? DexAttr.NON_SHINY : DexAttr.SHINY;
-      this.dexAttrCursor |= (female !== undefined ? !female : !(female = oldProps.female)) ? DexAttr.MALE : DexAttr.FEMALE;
-      this.dexAttrCursor |= (variant !== undefined ? !variant : !(variant = oldProps.variant)) ? DexAttr.DEFAULT_VARIANT : variant === 1 ? DexAttr.VARIANT_2 : DexAttr.VARIANT_3;
-      this.dexAttrCursor |= this.scene.gameData.getFormAttr(formIndex !== undefined ? formIndex : (formIndex = oldProps.formIndex));
+      this.dexAttrCursor |= (shiny !== undefined ? !shiny : !(shiny = oldProps?.shiny)) ? DexAttr.NON_SHINY : DexAttr.SHINY;
+      this.dexAttrCursor |= (female !== undefined ? !female : !(female = oldProps?.female)) ? DexAttr.MALE : DexAttr.FEMALE;
+      this.dexAttrCursor |= (variant !== undefined ? !variant : !(variant = oldProps?.variant)) ? DexAttr.DEFAULT_VARIANT : variant === 1 ? DexAttr.VARIANT_2 : DexAttr.VARIANT_3;
+      this.dexAttrCursor |= this.scene.gameData.getFormAttr(formIndex !== undefined ? formIndex : (formIndex = oldProps!.formIndex)); // TODO: is this bang correct?
       this.abilityCursor = abilityIndex !== undefined ? abilityIndex : (abilityIndex = oldAbilityIndex);
       this.natureCursor = natureIndex !== undefined ? natureIndex : (natureIndex = oldNatureIndex);
     }
@@ -2717,7 +2718,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
         }
       }
 
-      this.shinyOverlay.setVisible(shiny);
+      this.shinyOverlay.setVisible(shiny ?? false); // TODO: is false the correct default?
       this.pokemonNumberText.setColor(this.getTextColor(shiny ? TextStyle.SUMMARY_GOLD : TextStyle.SUMMARY, false));
       this.pokemonNumberText.setShadowColor(this.getTextColor(shiny ? TextStyle.SUMMARY_GOLD : TextStyle.SUMMARY, true));
 
@@ -2733,16 +2734,16 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
         const assetLoadCancelled = new Utils.BooleanHolder(false);
         this.assetLoadCancelled = assetLoadCancelled;
 
-        species.loadAssets(this.scene, female, formIndex, shiny, variant, true).then(() => {
+        species.loadAssets(this.scene, female!, formIndex, shiny, variant, true).then(() => { // TODO: is this bang correct?
           if (assetLoadCancelled.value) {
             return;
           }
           this.assetLoadCancelled = null;
           this.speciesLoaded.set(species.speciesId, true);
-          this.pokemonSprite.play(species.getSpriteKey(female, formIndex, shiny, variant));
+          this.pokemonSprite.play(species.getSpriteKey(female!, formIndex, shiny, variant)); // TODO: is this bang correct?
           this.pokemonSprite.setPipelineData("shiny", shiny);
           this.pokemonSprite.setPipelineData("variant", variant);
-          this.pokemonSprite.setPipelineData("spriteKey", species.getSpriteKey(female, formIndex, shiny, variant));
+          this.pokemonSprite.setPipelineData("spriteKey", species.getSpriteKey(female!, formIndex, shiny, variant)); // TODO: is this bang correct?
           this.pokemonSprite.setVisible(!this.statsMode);
         });
 
@@ -2750,7 +2751,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
         const isValidForChallenge = new Utils.BooleanHolder(true);
         Challenge.applyChallenges(this.scene.gameMode, Challenge.ChallengeType.STARTER_CHOICE, species, isValidForChallenge, this.scene.gameData.getSpeciesDexAttrProps(species, this.dexAttrCursor), !!this.starterSpecies.length);
         const starterSprite = this.filteredStarterContainers[this.cursor].icon as Phaser.GameObjects.Sprite;
-        starterSprite.setTexture(species.getIconAtlasKey(formIndex, shiny, variant), species.getIconId(female, formIndex, shiny, variant));
+        starterSprite.setTexture(species.getIconAtlasKey(formIndex, shiny, variant), species.getIconId(female!, formIndex, shiny, variant)); // TODO: is this bang correct?
         this.filteredStarterContainers[this.cursor].checkIconId(female, formIndex, shiny, variant);
         this.canCycleShiny = !!(dexEntry.caughtAttr & DexAttr.NON_SHINY && dexEntry.caughtAttr & DexAttr.SHINY);
         this.canCycleGender = !!(dexEntry.caughtAttr & DexAttr.MALE && dexEntry.caughtAttr & DexAttr.FEMALE);
@@ -2758,7 +2759,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
         this.canCycleForm = species.forms.filter(f => f.isStarterSelectable || !pokemonFormChanges[species.speciesId]?.find(fc => fc.formKey))
           .map((_, f) => dexEntry.caughtAttr & this.scene.gameData.getFormAttr(f)).filter(f => f).length > 1;
         this.canCycleNature = this.scene.gameData.getNaturesForAttr(dexEntry.natureAttr).length > 1;
-        this.canCycleVariant = shiny && [ dexEntry.caughtAttr & DexAttr.DEFAULT_VARIANT, dexEntry.caughtAttr & DexAttr.VARIANT_2, dexEntry.caughtAttr & DexAttr.VARIANT_3].filter(v => v).length > 1;
+        this.canCycleVariant = !!shiny && [ dexEntry.caughtAttr & DexAttr.DEFAULT_VARIANT, dexEntry.caughtAttr & DexAttr.VARIANT_2, dexEntry.caughtAttr & DexAttr.VARIANT_3].filter(v => v).length > 1;
       }
 
       if (dexEntry.caughtAttr && species.malePercent !== null) {
@@ -2771,7 +2772,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
       }
 
       if (dexEntry.caughtAttr) {
-        const ability = this.lastSpecies.getAbility(abilityIndex);
+        const ability = this.lastSpecies.getAbility(abilityIndex!); // TODO: is this bang correct?
         this.pokemonAbilityText.setText(allAbilities[ability].name);
 
         const isHidden = abilityIndex === (this.lastSpecies.ability2 ? 2 : 1);
@@ -2786,7 +2787,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
         this.pokemonNatureText.setText(getNatureName(natureIndex as unknown as Nature, true, true, false, this.scene.uiTheme));
 
         let levelMoves: LevelMoves;
-        if (pokemonFormLevelMoves.hasOwnProperty(species.speciesId) && pokemonFormLevelMoves[species.speciesId].hasOwnProperty(formIndex)) {
+        if (pokemonFormLevelMoves.hasOwnProperty(species.speciesId) && formIndex && pokemonFormLevelMoves[species.speciesId].hasOwnProperty(formIndex)) {
           levelMoves = pokemonFormLevelMoves[species.speciesId][formIndex];
         } else {
           levelMoves = pokemonSpeciesLevelMoves[species.speciesId];
@@ -2801,41 +2802,42 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
         }
 
         const speciesMoveData = this.scene.gameData.starterData[species.speciesId].moveset;
-        const moveData: StarterMoveset = speciesMoveData
+        const moveData: StarterMoveset | null = speciesMoveData
           ? Array.isArray(speciesMoveData)
             ? speciesMoveData as StarterMoveset
-            : (speciesMoveData as StarterFormMoveData)[formIndex]
+            : (speciesMoveData as StarterFormMoveData)[formIndex!] // TODO: is this bang correct?
           : null;
         const availableStarterMoves = this.speciesStarterMoves.concat(speciesEggMoves.hasOwnProperty(species.speciesId) ? speciesEggMoves[species.speciesId].filter((_, em: integer) => this.scene.gameData.starterData[species.speciesId].eggMoves & (1 << em)) : []);
         this.starterMoveset = (moveData || (this.speciesStarterMoves.slice(0, 4) as StarterMoveset)).filter(m => availableStarterMoves.find(sm => sm === m)) as StarterMoveset;
         // Consolidate move data if it contains an incompatible move
         if (this.starterMoveset.length < 4 && this.starterMoveset.length < availableStarterMoves.length) {
-          this.starterMoveset.push(...availableStarterMoves.filter(sm => this.starterMoveset.indexOf(sm) === -1).slice(0, 4 - this.starterMoveset.length));
+          this.starterMoveset.push(...availableStarterMoves.filter(sm => this.starterMoveset?.indexOf(sm) === -1).slice(0, 4 - this.starterMoveset.length));
         }
 
         // Remove duplicate moves
         this.starterMoveset = this.starterMoveset.filter(
           (move, i) => {
-            return this.starterMoveset.indexOf(move) === i;
+            return this.starterMoveset?.indexOf(move) === i;
           }) as StarterMoveset;
 
-        const speciesForm = getPokemonSpeciesForm(species.speciesId, formIndex);
-        const formText = Utils.capitalizeString(species?.forms[formIndex]?.formKey, "-", false, false);
+        const speciesForm = getPokemonSpeciesForm(species.speciesId, formIndex!); // TODO: is the bang correct?
+        const formText = Utils.capitalizeString(species?.forms[formIndex!]?.formKey, "-", false, false); // TODO: is the bang correct?
 
         const speciesName = Utils.capitalizeString(Species[species.speciesId], "_", true, false);
 
         if (species.speciesId === Species.ARCEUS) {
-          this.pokemonFormText.setText(i18next.t(`pokemonInfo:Type.${formText.toUpperCase()}`));
+          this.pokemonFormText.setText(i18next.t(`pokemonInfo:Type.${formText?.toUpperCase()}`));
         } else {
           this.pokemonFormText.setText(formText ? i18next.t(`pokemonForm:${speciesName}${formText}`) : "");
         }
 
-        this.setTypeIcons(speciesForm.type1, speciesForm.type2);
+        this.setTypeIcons(speciesForm.type1, speciesForm.type2!); // TODO: is this bang correct?
       } else {
         this.pokemonAbilityText.setText("");
         this.pokemonPassiveText.setText("");
         this.pokemonNatureText.setText("");
-        this.setTypeIcons(null, null);
+        // @ts-ignore
+        this.setTypeIcons(null, null); // TODO: resolve ts-ignore.. huh!?
       }
     } else {
       this.shinyOverlay.setVisible(false);
@@ -2845,7 +2847,8 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
       this.pokemonAbilityText.setText("");
       this.pokemonPassiveText.setText("");
       this.pokemonNatureText.setText("");
-      this.setTypeIcons(null, null);
+      // @ts-ignore
+      this.setTypeIcons(null, null); // TODO: resolve ts-ignore.. huh!?
     }
 
     if (!this.starterMoveset) {
@@ -2868,7 +2871,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
       this.pokemonEggMoveLabels[em].setText(eggMove && eggMoveUnlocked ? eggMove.name : "???");
     }
 
-    this.pokemonEggMovesContainer.setVisible(this.speciesStarterDexEntry?.caughtAttr && hasEggMoves);
+    this.pokemonEggMovesContainer.setVisible(!!this.speciesStarterDexEntry?.caughtAttr && hasEggMoves);
 
     this.pokemonAdditionalMoveCountLabel.setText(`(+${Math.max(this.speciesStarterMoves.length - 4, 0)})`);
     this.pokemonAdditionalMoveCountLabel.setVisible(this.speciesStarterMoves.length > 4);
@@ -3064,7 +3067,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
           this.scene.pushPhase(new TitlePhase(this.scene));
         }
         this.clearText();
-        this.scene.getCurrentPhase().end();
+        this.scene.getCurrentPhase()?.end();
       }, cancel, null, null, 19);
     });
 
@@ -3097,7 +3100,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
             const thisObj = this;
             const originalStarterSelectCallback = this.starterSelectCallback;
             this.starterSelectCallback = null;
-            originalStarterSelectCallback(new Array(this.starterSpecies.length).fill(0).map(function (_, i) {
+            originalStarterSelectCallback && originalStarterSelectCallback(new Array(this.starterSpecies.length).fill(0).map(function (_, i) {
               const starterSpecies = thisObj.starterSpecies[i];
               return {
                 species: starterSpecies,
@@ -3116,7 +3119,7 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
     } else {
       const handler = this.scene.ui.getHandler() as AwaitableUiHandler;
       handler.tutorialActive = true;
-      this.scene.ui.showText(i18next.t("starterSelectUiHandler:invalidParty"), null, () => this.scene.ui.showText(null, 0, () => handler.tutorialActive = false), null, true);
+      this.scene.ui.showText(i18next.t("starterSelectUiHandler:invalidParty"), null, () => this.scene.ui.showText("", 0, () => handler.tutorialActive = false), null, true);
     }
     return true;
   }
@@ -3147,7 +3150,8 @@ export default class StarterSelectUiHandler extends MessageUiHandler {
       this.statsMode = false;
       this.statsContainer.setVisible(false);
       this.pokemonSprite.setVisible(!!this.speciesStarterDexEntry?.caughtAttr);
-      this.statsContainer.updateIvs(null);
+      //@ts-ignore
+      this.statsContainer.updateIvs(null); // TODO: resolve ts-ignore. !?!?
     }
   }
 
diff --git a/src/ui/summary-ui-handler.ts b/src/ui/summary-ui-handler.ts
index 405429fcd3f..030e67fcc30 100644
--- a/src/ui/summary-ui-handler.ts
+++ b/src/ui/summary-ui-handler.ts
@@ -2,7 +2,7 @@ import BattleScene, { starterColors } from "../battle-scene";
 import { Mode } from "./ui";
 import UiHandler from "./ui-handler";
 import * as Utils from "../utils";
-import { PlayerPokemon } from "../field/pokemon";
+import { PlayerPokemon, PokemonMove } from "../field/pokemon";
 import { getStarterValueFriendshipCap, speciesStarters } from "../data/pokemon-species";
 import { argbFromRgba } from "@material/material-color-utilities";
 import { Type, getTypeRgb } from "../data/type";
@@ -24,7 +24,6 @@ import i18next from "i18next";
 import {modifierSortFunc} from "../modifier/modifier";
 import { PlayerGender } from "#enums/player-gender";
 
-
 enum Page {
   PROFILE,
   STATS,
@@ -41,11 +40,11 @@ interface abilityContainer {
   /** An image displaying the summary label */
   labelImage: Phaser.GameObjects.Image,
   /** The ability object */
-  ability: Ability,
+  ability: Ability | null,
   /** The text object displaying the name of the ability */
-  nameText: Phaser.GameObjects.Text,
+  nameText: Phaser.GameObjects.Text | null,
   /** The text object displaying the description of the ability */
-  descriptionText: Phaser.GameObjects.Text,
+  descriptionText: Phaser.GameObjects.Text | null,
 }
 
 export default class SummaryUiHandler extends UiHandler {
@@ -79,8 +78,8 @@ export default class SummaryUiHandler extends UiHandler {
   private summaryPageContainer: Phaser.GameObjects.Container;
   private movesContainer: Phaser.GameObjects.Container;
   private moveDescriptionText: Phaser.GameObjects.Text;
-  private moveCursorObj: Phaser.GameObjects.Sprite;
-  private selectedMoveCursorObj: Phaser.GameObjects.Sprite;
+  private moveCursorObj: Phaser.GameObjects.Sprite | null;
+  private selectedMoveCursorObj: Phaser.GameObjects.Sprite | null;
   private moveRowsContainer: Phaser.GameObjects.Container;
   private extraMoveRowContainer: Phaser.GameObjects.Container;
   private moveEffectContainer: Phaser.GameObjects.Container;
@@ -89,14 +88,14 @@ export default class SummaryUiHandler extends UiHandler {
   private moveCategoryIcon: Phaser.GameObjects.Sprite;
   private summaryPageTransitionContainer: Phaser.GameObjects.Container;
 
-  private descriptionScrollTween: Phaser.Tweens.Tween;
-  private moveCursorBlinkTimer: Phaser.Time.TimerEvent;
+  private descriptionScrollTween: Phaser.Tweens.Tween | null;
+  private moveCursorBlinkTimer: Phaser.Time.TimerEvent | null;
 
-  private pokemon: PlayerPokemon;
+  private pokemon: PlayerPokemon | null;
   private playerParty: boolean;
   /**This is set to false when checking the summary of a freshly caught Pokemon as it is not part of a player's party yet but still needs to display its items**/
-  private newMove: Move;
-  private moveSelectFunction: Function;
+  private newMove: Move | null;
+  private moveSelectFunction: Function | null;
   private transitioning: boolean;
   private statusVisible: boolean;
   private moveEffectsVisible: boolean;
@@ -104,7 +103,7 @@ export default class SummaryUiHandler extends UiHandler {
   private moveSelect: boolean;
   private moveCursor: integer;
   private selectedMoveIndex: integer;
-  private selectCallback: Function;
+  private selectCallback: Function | null;
 
   constructor(scene: BattleScene) {
     super(scene, Mode.SUMMARY);
@@ -138,7 +137,7 @@ export default class SummaryUiHandler extends UiHandler {
     this.numberText.setOrigin(0, 1);
     this.summaryContainer.add(this.numberText);
 
-    this.pokemonSprite = this.scene.initPokemonSprite(this.scene.add.sprite(56, -106, "pkmn__sub"), null, false, true);
+    this.pokemonSprite = this.scene.initPokemonSprite(this.scene.add.sprite(56, -106, "pkmn__sub"), undefined, false, true);
     this.summaryContainer.add(this.pokemonSprite);
 
     this.nameText = addTextObject(this.scene, 6, -54, "", TextStyle.SUMMARY);
@@ -305,10 +304,10 @@ export default class SummaryUiHandler extends UiHandler {
     this.pokemonSprite.setPipelineData("variant", this.pokemon.variant);
     [ "spriteColors", "fusionSpriteColors" ].map(k => {
       delete this.pokemonSprite.pipelineData[`${k}Base`];
-      if (this.pokemon.summonData?.speciesForm) {
+      if (this.pokemon?.summonData?.speciesForm) {
         k += "Base";
       }
-      this.pokemonSprite.pipelineData[k] = this.pokemon.getSprite().pipelineData[k];
+      this.pokemonSprite.pipelineData[k] = this.pokemon?.getSprite().pipelineData[k];
     });
     this.pokemon.cry();
 
@@ -319,7 +318,7 @@ export default class SummaryUiHandler extends UiHandler {
     this.splicedIcon.setPositionRelative(this.nameText, this.nameText.displayWidth + 2, 3);
     this.splicedIcon.setVisible(isFusion);
     if (this.splicedIcon.visible) {
-      this.splicedIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip(null, `${this.pokemon.species.getName(this.pokemon.formIndex)}/${this.pokemon.fusionSpecies.getName(this.pokemon.fusionFormIndex)}`, true));
+      this.splicedIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip("", `${this.pokemon?.species.getName(this.pokemon.formIndex)}/${this.pokemon?.fusionSpecies?.getName(this.pokemon?.fusionFormIndex)}`, true));
       this.splicedIcon.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
     }
 
@@ -338,7 +337,7 @@ export default class SummaryUiHandler extends UiHandler {
     const candyCropY = 16 - (16 * (currentFriendship / friendshipCap));
 
     if (this.candyShadow.visible) {
-      this.candyShadow.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip(null, `${currentFriendship}/${friendshipCap}`, true));
+      this.candyShadow.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip("", `${currentFriendship}/${friendshipCap}`, true));
       this.candyShadow.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
     }
 
@@ -357,7 +356,7 @@ export default class SummaryUiHandler extends UiHandler {
       const shinyDescriptor = doubleShiny || baseVariant ?
         `${baseVariant === 2 ? i18next.t("common:epicShiny") : baseVariant === 1 ? i18next.t("common:rareShiny") : i18next.t("common:commonShiny")}${doubleShiny ? `/${this.pokemon.fusionVariant === 2 ? i18next.t("common:epicShiny") : this.pokemon.fusionVariant === 1 ? i18next.t("common:rareShiny") : i18next.t("common:commonShiny")}` : ""}`
         : "";
-      this.shinyIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip(null, `${i18next.t("common:shinyOnHover")}${shinyDescriptor ? ` (${shinyDescriptor})` : ""}`, true));
+      this.shinyIcon.on("pointerover", () => (this.scene as BattleScene).ui.showTooltip("", `${i18next.t("common:shinyOnHover")}${shinyDescriptor ? ` (${shinyDescriptor})` : ""}`, true));
       this.shinyIcon.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
     }
 
@@ -416,16 +415,16 @@ export default class SummaryUiHandler extends UiHandler {
 
     if (this.moveSelect) {
       if (button === Button.ACTION) {
-        if (this.moveCursor < this.pokemon.moveset.length) {
+        if (this.pokemon && this.moveCursor < this.pokemon.moveset.length) {
           if (this.summaryUiMode === SummaryUiMode.LEARN_MOVE) {
-            this.moveSelectFunction(this.moveCursor);
+            this.moveSelectFunction && this.moveSelectFunction(this.moveCursor);
           } else {
             if (this.selectedMoveIndex === -1) {
               this.selectedMoveIndex = this.moveCursor;
               this.setCursor(this.moveCursor);
             } else {
               if (this.selectedMoveIndex !== this.moveCursor) {
-                const tempMove = this.pokemon.moveset[this.selectedMoveIndex];
+                const tempMove = this.pokemon?.moveset[this.selectedMoveIndex];
                 this.pokemon.moveset[this.selectedMoveIndex] = this.pokemon.moveset[this.moveCursor];
                 this.pokemon.moveset[this.moveCursor] = tempMove;
 
@@ -483,15 +482,15 @@ export default class SummaryUiHandler extends UiHandler {
         if (this.cursor === Page.MOVES) {
           this.showMoveSelect();
           success = true;
-        } else if (this.cursor === Page.PROFILE && this.pokemon.hasPassive()) {
+        } else if (this.cursor === Page.PROFILE && this.pokemon?.hasPassive()) {
           // if we're on the PROFILE page and this pokemon has a passive unlocked..
           // Since abilities are displayed by default, all we need to do is toggle visibility on all elements to show passives
-          this.abilityContainer.nameText.setVisible(!this.abilityContainer.descriptionText.visible);
-          this.abilityContainer.descriptionText.setVisible(!this.abilityContainer.descriptionText.visible);
+          this.abilityContainer.nameText?.setVisible(!this.abilityContainer.descriptionText?.visible);
+          this.abilityContainer.descriptionText?.setVisible(!this.abilityContainer.descriptionText.visible);
           this.abilityContainer.labelImage.setVisible(!this.abilityContainer.labelImage.visible);
 
-          this.passiveContainer.nameText.setVisible(!this.passiveContainer.descriptionText.visible);
-          this.passiveContainer.descriptionText.setVisible(!this.passiveContainer.descriptionText.visible);
+          this.passiveContainer.nameText?.setVisible(!this.passiveContainer.descriptionText?.visible);
+          this.passiveContainer.descriptionText?.setVisible(!this.passiveContainer.descriptionText.visible);
           this.passiveContainer.labelImage.setVisible(!this.passiveContainer.labelImage.visible);
         }
       } else if (button === Button.CANCEL) {
@@ -523,7 +522,7 @@ export default class SummaryUiHandler extends UiHandler {
           }
           const isDown = button === Button.DOWN;
           const party = this.scene.getParty();
-          const partyMemberIndex = party.indexOf(this.pokemon);
+          const partyMemberIndex = this.pokemon ? party.indexOf(this.pokemon) : -1;
           if ((isDown && partyMemberIndex < party.length - 1) || (!isDown && partyMemberIndex)) {
             const page = this.cursor;
             this.clear();
@@ -609,7 +608,7 @@ export default class SummaryUiHandler extends UiHandler {
         loop: true,
         delay: Utils.fixedInt(600),
         callback: () => {
-          this.moveCursorObj.setVisible(false);
+          this.moveCursorObj?.setVisible(false);
           this.scene.time.delayedCall(Utils.fixedInt(100), () => {
             if (!this.moveCursorObj) {
               return;
@@ -727,16 +726,16 @@ export default class SummaryUiHandler extends UiHandler {
         return typeIcon;
       };
 
-      const types = this.pokemon.getTypes(false, false, true);
+      const types = this.pokemon?.getTypes(false, false, true)!; // TODO: is this bang correct?
       profileContainer.add(getTypeIcon(0, types[0]));
       if (types.length > 1) {
         profileContainer.add(getTypeIcon(1, types[1]));
       }
-      if (this.pokemon.isTerastallized()) {
+      if (this.pokemon?.isTerastallized()) {
         profileContainer.add(getTypeIcon(types.length, this.pokemon.getTeraType(), true));
       }
 
-      if (this.pokemon.getLuck()) {
+      if (this.pokemon?.getLuck()) {
         const luckLabelText = addTextObject(this.scene, 141, 28, i18next.t("common:luckIndicator"), TextStyle.SUMMARY_ALT);
         luckLabelText.setOrigin(0, 0);
         profileContainer.add(luckLabelText);
@@ -749,13 +748,13 @@ export default class SummaryUiHandler extends UiHandler {
 
       this.abilityContainer = {
         labelImage: this.scene.add.image(0, 0, "summary_profile_ability"),
-        ability: this.pokemon.getAbility(true),
+        ability: this.pokemon?.getAbility(true)!, // TODO: is this bang correct?
         nameText: null,
         descriptionText: null};
 
       const allAbilityInfo = [this.abilityContainer]; // Creates an array to iterate through
       // Only add to the array and set up displaying a passive if it's unlocked
-      if (this.pokemon.hasPassive()) {
+      if (this.pokemon?.hasPassive()) {
         this.passiveContainer = {
           labelImage: this.scene.add.image(0, 0, "summary_profile_passive"),
           ability: this.pokemon.getPassiveAbility(),
@@ -777,11 +776,11 @@ export default class SummaryUiHandler extends UiHandler {
         abilityInfo.labelImage.setOrigin(0, 0);
         profileContainer.add(abilityInfo.labelImage);
 
-        abilityInfo.nameText = addTextObject(this.scene, 7, 66, abilityInfo.ability.name, TextStyle.SUMMARY_ALT);
+        abilityInfo.nameText = addTextObject(this.scene, 7, 66, abilityInfo.ability?.name!, TextStyle.SUMMARY_ALT); // TODO: is this bang correct?
         abilityInfo.nameText.setOrigin(0, 1);
         profileContainer.add(abilityInfo.nameText);
 
-        abilityInfo.descriptionText = addTextObject(this.scene, 7, 69, abilityInfo.ability.description, TextStyle.WINDOW_ALT, { wordWrap: { width: 1224 } });
+        abilityInfo.descriptionText = addTextObject(this.scene, 7, 69, abilityInfo.ability?.description!, TextStyle.WINDOW_ALT, { wordWrap: { width: 1224 } }); // TODO: is this bang correct?
         abilityInfo.descriptionText.setOrigin(0, 0);
         profileContainer.add(abilityInfo.descriptionText);
 
@@ -813,17 +812,17 @@ export default class SummaryUiHandler extends UiHandler {
       });
       // Turn off visibility of passive info by default
       this.passiveContainer?.labelImage.setVisible(false);
-      this.passiveContainer?.nameText.setVisible(false);
-      this.passiveContainer?.descriptionText.setVisible(false);
+      this.passiveContainer?.nameText?.setVisible(false);
+      this.passiveContainer?.descriptionText?.setVisible(false);
 
       const closeFragment = getBBCodeFrag("", TextStyle.WINDOW_ALT);
-      const rawNature = Utils.toReadableString(Nature[this.pokemon.getNature()]);
-      const nature = `${getBBCodeFrag(Utils.toReadableString(getNatureName(this.pokemon.getNature())), TextStyle.SUMMARY_RED)}${closeFragment}`;
+      const rawNature = Utils.toReadableString(Nature[this.pokemon?.getNature()!]); // TODO: is this bang correct?
+      const nature = `${getBBCodeFrag(Utils.toReadableString(getNatureName(this.pokemon?.getNature()!)), TextStyle.SUMMARY_RED)}${closeFragment}`; // TODO: is this bang correct?
 
       const memoString = i18next.t("pokemonSummary:memoString", {
-        metFragment: i18next.t(`pokemonSummary:metFragment.${this.pokemon.metBiome === -1? "apparently": "normal"}`, {
-          biome: `${getBBCodeFrag(getBiomeName(this.pokemon.metBiome), TextStyle.SUMMARY_RED)}${closeFragment}`,
-          level: `${getBBCodeFrag(this.pokemon.metLevel.toString(), TextStyle.SUMMARY_RED)}${closeFragment}`,
+        metFragment: i18next.t(`pokemonSummary:metFragment.${this.pokemon?.metBiome === -1? "apparently": "normal"}`, {
+          biome: `${getBBCodeFrag(getBiomeName(this.pokemon?.metBiome!), TextStyle.SUMMARY_RED)}${closeFragment}`, // TODO: is this bang correct?
+          level: `${getBBCodeFrag(this.pokemon?.metLevel.toString()!, TextStyle.SUMMARY_RED)}${closeFragment}`, // TODO: is this bang correct?
         }),
         natureFragment:
           i18next.exists(`pokemonSummary:natureFragment.${rawNature}`) ?
@@ -831,7 +830,7 @@ export default class SummaryUiHandler extends UiHandler {
             nature,
       });
 
-      const memoText = addBBCodeTextObject(this.scene, 7, 113, memoString, TextStyle.WINDOW_ALT);
+      const memoText = addBBCodeTextObject(this.scene, 7, 113, String(memoString), TextStyle.WINDOW_ALT);
       memoText.setOrigin(0, 0);
       profileContainer.add(memoText);
       break;
@@ -846,15 +845,15 @@ export default class SummaryUiHandler extends UiHandler {
         const rowIndex = s % 3;
         const colIndex = Math.floor(s / 3);
 
-        const natureStatMultiplier = getNatureStatMultiplier(this.pokemon.getNature(), s);
+        const natureStatMultiplier = getNatureStatMultiplier(this.pokemon?.getNature()!, s); // TODO: is this bang correct?
 
         const statLabel = addTextObject(this.scene, 27 + 115 * colIndex + (colIndex === 1 ?  5 : 0), 56 + 16 * rowIndex, statName, natureStatMultiplier === 1 ? TextStyle.SUMMARY : natureStatMultiplier > 1 ? TextStyle.SUMMARY_PINK : TextStyle.SUMMARY_BLUE);
         statLabel.setOrigin(0.5, 0);
         statsContainer.add(statLabel);
 
         const statValueText = stat !== Stat.HP
-          ? Utils.formatStat(this.pokemon.stats[s])
-          : `${Utils.formatStat(this.pokemon.hp, true)}/${Utils.formatStat(this.pokemon.getMaxHp(), true)}`;
+          ? Utils.formatStat(this.pokemon?.stats[s]!) // TODO: is this bang correct?
+          : `${Utils.formatStat(this.pokemon?.hp!, true)}/${Utils.formatStat(this.pokemon?.getMaxHp()!, true)}`; // TODO: are those bangs correct?
 
         const statValue = addTextObject(this.scene, 120 + 88 * colIndex, 56 + 16 * rowIndex, statValueText, TextStyle.WINDOW_ALT);
         statValue.setOrigin(1, 0);
@@ -862,7 +861,7 @@ export default class SummaryUiHandler extends UiHandler {
       });
 
       const itemModifiers = (this.scene.findModifiers(m => m instanceof PokemonHeldItemModifier
-          && m.pokemonId === this.pokemon.id, this.playerParty) as PokemonHeldItemModifier[])
+          && m.pokemonId === this.pokemon?.id, this.playerParty) as PokemonHeldItemModifier[])
         .sort(modifierSortFunc);
 
       itemModifiers.forEach((item, i) => {
@@ -876,8 +875,12 @@ export default class SummaryUiHandler extends UiHandler {
         icon.on("pointerout", () => (this.scene as BattleScene).ui.hideTooltip());
       });
 
-      const relLvExp = getLevelRelExp(this.pokemon.level + 1, this.pokemon.species.growthRate);
-      const expRatio = this.pokemon.level < this.scene.getMaxExpLevel() ? this.pokemon.levelExp / relLvExp : 0;
+      const pkmLvl = this.pokemon?.level!; // TODO: is this bang correct?
+      const pkmLvlExp = this.pokemon?.levelExp!; // TODO: is this bang correct?
+      const pkmExp = this.pokemon?.exp!; // TODO: is this bang correct?
+      const pkmSpeciesGrowthRate = this.pokemon?.species.growthRate!; // TODO: is this bang correct?
+      const relLvExp = getLevelRelExp(pkmLvl + 1, pkmSpeciesGrowthRate);
+      const expRatio = pkmLvl < this.scene.getMaxExpLevel() ? pkmLvlExp / relLvExp : 0;
 
       const expLabel = addTextObject(this.scene, 6, 112, i18next.t("pokemonSummary:expPoints"), TextStyle.SUMMARY);
       expLabel.setOrigin(0, 0);
@@ -887,12 +890,12 @@ export default class SummaryUiHandler extends UiHandler {
       nextLvExpLabel.setOrigin(0, 0);
       statsContainer.add(nextLvExpLabel);
 
-      const expText = addTextObject(this.scene, 208, 112, this.pokemon.exp.toString(), TextStyle.WINDOW_ALT);
+      const expText = addTextObject(this.scene, 208, 112, pkmExp.toString(), TextStyle.WINDOW_ALT);
       expText.setOrigin(1, 0);
       statsContainer.add(expText);
 
-      const nextLvExp = this.pokemon.level < this.scene.getMaxExpLevel()
-        ? getLevelTotalExp(this.pokemon.level + 1, this.pokemon.species.growthRate) - this.pokemon.exp
+      const nextLvExp = pkmLvl < this.scene.getMaxExpLevel()
+        ? getLevelTotalExp(pkmLvl + 1, pkmSpeciesGrowthRate) - pkmExp
         : 0;
       const nextLvExpText = addTextObject(this.scene, 208, 128, nextLvExp.toString(), TextStyle.WINDOW_ALT);
       nextLvExpText.setOrigin(1, 0);
@@ -924,14 +927,14 @@ export default class SummaryUiHandler extends UiHandler {
       extraRowOverlay.setOrigin(0, 1);
       this.extraMoveRowContainer.add(extraRowOverlay);
 
-      const extraRowText = addTextObject(this.scene, 35, 0, this.summaryUiMode === SummaryUiMode.LEARN_MOVE ? this.newMove.name : i18next.t("pokemonSummary:cancel"),
+      const extraRowText = addTextObject(this.scene, 35, 0, this.summaryUiMode === SummaryUiMode.LEARN_MOVE && this.newMove ? this.newMove.name : i18next.t("pokemonSummary:cancel"),
         this.summaryUiMode === SummaryUiMode.LEARN_MOVE ? TextStyle.SUMMARY_PINK : TextStyle.SUMMARY);
       extraRowText.setOrigin(0, 1);
       this.extraMoveRowContainer.add(extraRowText);
 
       if (this.summaryUiMode === SummaryUiMode.LEARN_MOVE) {
         this.extraMoveRowContainer.setVisible(true);
-        const newMoveTypeIcon = this.scene.add.sprite(0, 0, `types${Utils.verifyLang(i18next.resolvedLanguage) ? `_${i18next.resolvedLanguage}` : ""}`, Type[this.newMove.type].toLowerCase());
+        const newMoveTypeIcon = this.scene.add.sprite(0, 0, `types${Utils.verifyLang(i18next.resolvedLanguage) ? `_${i18next.resolvedLanguage}` : ""}`, Type[this.newMove?.type!].toLowerCase()); // TODO: is this bang correct?
         newMoveTypeIcon.setOrigin(0, 1);
         this.extraMoveRowContainer.add(newMoveTypeIcon);
 
@@ -939,7 +942,7 @@ export default class SummaryUiHandler extends UiHandler {
         ppOverlay.setOrigin(0, 1);
         this.extraMoveRowContainer.add(ppOverlay);
 
-        const pp = Utils.padInt(this.newMove.pp, 2, "  ");
+        const pp = Utils.padInt(this.newMove?.pp!, 2, "  "); // TODO: is this bang correct?
         const ppText = addTextObject(this.scene, 173, 1, `${pp}/${pp}`, TextStyle.WINDOW);
         ppText.setOrigin(0, 1);
         this.extraMoveRowContainer.add(ppText);
@@ -949,7 +952,7 @@ export default class SummaryUiHandler extends UiHandler {
       this.movesContainer.add(this.moveRowsContainer);
 
       for (let m = 0; m < 4; m++) {
-        const move = m < this.pokemon.moveset.length ? this.pokemon.moveset[m] : null;
+        const move: PokemonMove | null = this.pokemon && this.pokemon.moveset.length > m ? this.pokemon?.moveset[m] : null;
         const moveRowContainer = this.scene.add.container(0, 16 * m);
         this.moveRowsContainer.add(moveRowContainer);
 
@@ -1020,13 +1023,13 @@ export default class SummaryUiHandler extends UiHandler {
     });
   }
 
-  getSelectedMove(): Move {
+  getSelectedMove(): Move | null {
     if (this.cursor !== Page.MOVES) {
       return null;
     }
 
-    if (this.moveCursor < 4 && this.moveCursor < this.pokemon.moveset.length) {
-      return this.pokemon.moveset[this.moveCursor].getMove();
+    if (this.moveCursor < 4 && this.pokemon && this.moveCursor < this.pokemon.moveset.length) {
+      return this.pokemon.moveset[this.moveCursor]!.getMove(); // TODO: is this bang correct?
     } else if (this.summaryUiMode === SummaryUiMode.LEARN_MOVE && this.moveCursor === 4) {
       return this.newMove;
     }
@@ -1043,7 +1046,7 @@ export default class SummaryUiHandler extends UiHandler {
 
   hideMoveSelect() {
     if (this.summaryUiMode === SummaryUiMode.LEARN_MOVE) {
-      this.moveSelectFunction(4);
+      this.moveSelectFunction && this.moveSelectFunction(4);
       return;
     }
 
diff --git a/src/ui/target-select-ui-handler.ts b/src/ui/target-select-ui-handler.ts
index 48799473343..9a0922715e8 100644
--- a/src/ui/target-select-ui-handler.ts
+++ b/src/ui/target-select-ui-handler.ts
@@ -18,7 +18,7 @@ export default class TargetSelectUiHandler extends UiHandler {
   private isMultipleTargets: boolean = false;
   private targets: BattlerIndex[];
   private targetsHighlighted: Pokemon[];
-  private targetFlashTween: Phaser.Tweens.Tween;
+  private targetFlashTween: Phaser.Tweens.Tween | null;
   private targetBattleInfoMoveTween: Phaser.Tweens.Tween[] = [];
 
   constructor(scene: BattleScene) {
@@ -68,12 +68,12 @@ export default class TargetSelectUiHandler extends UiHandler {
       switch (button) {
       case Button.UP:
         if (this.cursor < BattlerIndex.ENEMY && this.targets.findIndex(t => t >= BattlerIndex.ENEMY) > -1) {
-          success = this.setCursor(this.targets.find(t => t >= BattlerIndex.ENEMY));
+          success = this.setCursor(this.targets.find(t => t >= BattlerIndex.ENEMY)!); // TODO: is the bang correct here?
         }
         break;
       case Button.DOWN:
         if (this.cursor >= BattlerIndex.ENEMY && this.targets.findIndex(t => t < BattlerIndex.ENEMY) > -1) {
-          success = this.setCursor(this.targets.find(t => t < BattlerIndex.ENEMY));
+          success = this.setCursor(this.targets.find(t => t < BattlerIndex.ENEMY)!); // TODO: is the bang correct here?
         }
         break;
       case Button.LEFT:
diff --git a/src/ui/text.ts b/src/ui/text.ts
index ab4a26b6e98..8b76c2f5c62 100644
--- a/src/ui/text.ts
+++ b/src/ui/text.ts
@@ -185,7 +185,7 @@ export function getTextStyleOptions(style: TextStyle, uiTheme: UiTheme, extraSty
 
   if (extraStyleOptions) {
     if (extraStyleOptions.fontSize) {
-      const sizeRatio = parseInt(extraStyleOptions.fontSize.toString().slice(0, -2)) / parseInt(styleOptions.fontSize.toString().slice(0, -2));
+      const sizeRatio = parseInt(extraStyleOptions.fontSize.toString().slice(0, -2)) / parseInt(styleOptions.fontSize?.toString().slice(0, -2) ?? "1");
       shadowXpos *= sizeRatio;
     }
     styleOptions = Object.assign(styleOptions, extraStyleOptions);
diff --git a/src/ui/time-of-day-widget.ts b/src/ui/time-of-day-widget.ts
index e71839a84c5..5d2f184e679 100644
--- a/src/ui/time-of-day-widget.ts
+++ b/src/ui/time-of-day-widget.ts
@@ -147,7 +147,10 @@ export default class TimeOfDayWidget extends Phaser.GameObjects.Container {
     // Swaps all elements of the icon arrays by shifting the first element onto the end of the array
     // This ensures index[0] is always the new time of day icon and index[1] is always the current one
     this.timeOfDayIconPairs.forEach(
-      icons => icons.push(icons.shift()));
+      icons => {
+        const shifted = icons.shift();
+        shifted && icons.push(shifted);
+      });
   }
 
   /**
diff --git a/src/ui/title-ui-handler.ts b/src/ui/title-ui-handler.ts
index e2a704f7541..3c25ed34d61 100644
--- a/src/ui/title-ui-handler.ts
+++ b/src/ui/title-ui-handler.ts
@@ -14,7 +14,7 @@ export default class TitleUiHandler extends OptionSelectUiHandler {
   private splashMessageText: Phaser.GameObjects.Text;
   private eventDisplay: TimedEventDisplay;
 
-  private titleStatsTimer: NodeJS.Timeout;
+  private titleStatsTimer: NodeJS.Timeout | null;
 
   constructor(scene: BattleScene, mode: Mode = Mode.TITLE) {
     super(scene, mode);
@@ -118,7 +118,7 @@ export default class TitleUiHandler extends OptionSelectUiHandler {
 
     this.eventDisplay?.clear();
 
-    clearInterval(this.titleStatsTimer);
+    this.titleStatsTimer && clearInterval(this.titleStatsTimer);
     this.titleStatsTimer = null;
 
     this.scene.tweens.add({
diff --git a/src/ui/ui-theme.ts b/src/ui/ui-theme.ts
index 58490e1c618..75725910b82 100644
--- a/src/ui/ui-theme.ts
+++ b/src/ui/ui-theme.ts
@@ -43,7 +43,7 @@ export function addWindow(scene: BattleScene, x: number, y: number, width: numbe
 
   const borderSize = scene.uiTheme ? 6 : 8;
 
-  const window = scene.add.nineslice(x, y, `window_${scene.windowType}${getWindowVariantSuffix(windowVariant)}`, null, width, height, borderSize, borderSize, borderSize, borderSize);
+  const window = scene.add.nineslice(x, y, `window_${scene.windowType}${getWindowVariantSuffix(windowVariant)}`, undefined, width, height, borderSize, borderSize, borderSize, borderSize);
   window.setOrigin(0, 0);
 
   if (mergeMaskLeft || mergeMaskTop || maskOffsetX || maskOffsetY) {
diff --git a/src/ui/ui.ts b/src/ui/ui.ts
index ec6e91fa526..8ea4270deb3 100644
--- a/src/ui/ui.ts
+++ b/src/ui/ui.ts
@@ -271,10 +271,10 @@ export default class UI extends Phaser.GameObjects.Container {
     return handler.processInput(button);
   }
 
-  showText(text: string, delay?: integer, callback?: Function, callbackDelay?: integer, prompt?: boolean, promptDelay?: integer): void {
+  showText(text: string, delay?: integer | null, callback?: Function | null, callbackDelay?: integer | null, prompt?: boolean | null, promptDelay?: integer | null): void {
     if (prompt && text.indexOf("$") > -1) {
       const messagePages = text.split(/\$/g).map(m => m.trim());
-      let showMessageAndCallback = () => callback();
+      let showMessageAndCallback = () => callback && callback();
       for (let p = messagePages.length - 1; p >= 0; p--) {
         const originalFunc = showMessageAndCallback;
         showMessageAndCallback = () => this.showText(messagePages[p], null, originalFunc, null, true);
@@ -290,18 +290,18 @@ export default class UI extends Phaser.GameObjects.Container {
     }
   }
 
-  showDialogue(text: string, name: string, delay: integer = 0, callback: Function, callbackDelay?: integer, promptDelay?: integer): void {
+  showDialogue(text: string, name: string | undefined, delay: integer | null = 0, callback: Function, callbackDelay?: integer, promptDelay?: integer): void {
     // First get the gender of the player (default male) (also used if UNSET)
     let playerGenderPrefix = "PGM";
     if ((this.scene as BattleScene).gameData.gender === PlayerGender.FEMALE) {
       playerGenderPrefix = "PGF";
     }
     // Add the prefix to the text
-    const localizationKey = playerGenderPrefix + text;
+    const localizationKey: string = playerGenderPrefix + text;
 
     // Get localized dialogue (if available)
     let hasi18n = false;
-    if (i18next.exists(localizationKey as ParseKeys) ) {
+    if (i18next.exists(localizationKey) ) {
       text = i18next.t(localizationKey as ParseKeys);
       hasi18n = true;
 
@@ -341,7 +341,7 @@ export default class UI extends Phaser.GameObjects.Container {
 
     const key = playerGenderPrefix + text;
 
-    if (i18next.exists(key as ParseKeys) ) {
+    if (i18next.exists(key) ) {
       if ((this.scene as BattleScene).skipSeenDialogues && (this.scene as BattleScene).gameData.getSeenDialogues()[key] === true) {
         return true;
       }
@@ -371,8 +371,8 @@ export default class UI extends Phaser.GameObjects.Container {
 
   update(): void {
     if (this.tooltipContainer.visible) {
-      const reverse = this.scene.game.input.mousePointer.x >= this.scene.game.canvas.width - this.tooltipBg.width * 6 - 12;
-      this.tooltipContainer.setPosition(!reverse ? this.scene.game.input.mousePointer.x / 6 + 2 : this.scene.game.input.mousePointer.x / 6 - this.tooltipBg.width - 2, this.scene.game.input.mousePointer.y / 6 + 2);
+      const reverse = this.scene.game.input.mousePointer && this.scene.game.input.mousePointer.x >= this.scene.game.canvas.width - this.tooltipBg.width * 6 - 12;
+      this.tooltipContainer.setPosition(!reverse ? this.scene.game.input.mousePointer!.x / 6 + 2 : this.scene.game.input.mousePointer!.x / 6 - this.tooltipBg.width - 2, this.scene.game.input.mousePointer!.y / 6 + 2); // TODO: are these bangs correct?
     }
   }
 
@@ -507,7 +507,7 @@ export default class UI extends Phaser.GameObjects.Container {
 
       const doRevertMode = () => {
         this.getHandler().clear();
-        this.mode = this.modeChain.pop();
+        this.mode = this.modeChain.pop()!; // TODO: is this bang correct?
         const touchControls = document.getElementById("touchControls");
         if (touchControls) {
           touchControls.dataset.uiMode = Mode[this.mode];
diff --git a/src/ui/unavailable-modal-ui-handler.ts b/src/ui/unavailable-modal-ui-handler.ts
index c864801d9b4..873bef4ba79 100644
--- a/src/ui/unavailable-modal-ui-handler.ts
+++ b/src/ui/unavailable-modal-ui-handler.ts
@@ -7,7 +7,7 @@ import * as Utils from "#app/utils";
 import i18next from "i18next";
 
 export default class UnavailableModalUiHandler extends ModalUiHandler {
-  private reconnectTimer: NodeJS.Timeout;
+  private reconnectTimer: NodeJS.Timeout | null;
   private reconnectDuration: number;
   private reconnectCallback: () => void;
 
diff --git a/src/ui/vouchers-ui-handler.ts b/src/ui/vouchers-ui-handler.ts
index 370859bed54..169d851599b 100644
--- a/src/ui/vouchers-ui-handler.ts
+++ b/src/ui/vouchers-ui-handler.ts
@@ -22,10 +22,10 @@ export default class VouchersUiHandler extends MessageUiHandler {
   private itemsTotal: integer;
   private scrollCursor: integer;
 
-  private cursorObj: Phaser.GameObjects.NineSlice;
+  private cursorObj: Phaser.GameObjects.NineSlice | null;
 
   constructor(scene: BattleScene, mode?: Mode) {
-    super(scene, mode);
+    super(scene, mode!); // TODO: is this bang correct?
 
     this.itemsTotal = Object.keys(vouchers).length;
     this.scrollCursor = 0;
@@ -192,7 +192,7 @@ export default class VouchersUiHandler extends MessageUiHandler {
     let updateVoucher = ret;
 
     if (!this.cursorObj) {
-      this.cursorObj = this.scene.add.nineslice(0, 0, "select_cursor_highlight", null, 16, 16, 1, 1, 1, 1);
+      this.cursorObj = this.scene.add.nineslice(0, 0, "select_cursor_highlight", undefined, 16, 16, 1, 1, 1, 1);
       this.cursorObj.setOrigin(0, 0);
       this.voucherIconsContainer.add(this.cursorObj);
       updateVoucher = true;
diff --git a/src/utils.ts b/src/utils.ts
index 6a816d5b84d..01a0b8faa42 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -116,7 +116,7 @@ export function randSeedWeightedItem<T>(items: T[]): T {
     : Phaser.Math.RND.weightedPick(items);
 }
 
-export function randSeedEasedWeightedItem<T>(items: T[], easingFunction: string = "Sine.easeIn"): T {
+export function randSeedEasedWeightedItem<T>(items: T[], easingFunction: string = "Sine.easeIn"): T | null {
   if (!items.length) {
     return null;
   }
@@ -246,16 +246,16 @@ export function formatStat(stat: integer, forHp: boolean = false): string {
   return formatLargeNumber(stat, forHp ? 100000 : 1000000);
 }
 
-export function getEnumKeys(enumType): string[] {
-  return Object.values(enumType).filter(v => isNaN(parseInt(v.toString()))).map(v => v.toString());
+export function getEnumKeys(enumType: any): string[] {
+  return Object.values(enumType).filter(v => isNaN(parseInt(v!.toString()))).map(v => v!.toString());
 }
 
-export function getEnumValues(enumType): integer[] {
-  return Object.values(enumType).filter(v => !isNaN(parseInt(v.toString()))).map(v => parseInt(v.toString()));
+export function getEnumValues(enumType: any): integer[] {
+  return Object.values(enumType).filter(v => !isNaN(parseInt(v!.toString()))).map(v => parseInt(v!.toString()));
 }
 
-export function executeIf<T>(condition: boolean, promiseFunc: () => Promise<T>): Promise<T> {
-  return condition ? promiseFunc() : new Promise<T>(resolve => resolve(null));
+export function executeIf<T>(condition: boolean, promiseFunc: () => Promise<T>): Promise<T | null> {
+  return condition ? promiseFunc() : new Promise<T | null>(resolve => resolve(null));
 }
 
 export const sessionIdKey = "pokerogue_sessionId";
@@ -432,7 +432,7 @@ export function deltaRgb(rgb1: integer[], rgb2: integer[]): integer {
 }
 
 export function rgbHexToRgba(hex: string) {
-  const color = hex.match(/^([\da-f]{2})([\da-f]{2})([\da-f]{2})$/i);
+  const color = hex.match(/^([\da-f]{2})([\da-f]{2})([\da-f]{2})$/i)!; // TODO: is this bang correct?
   return {
     r: parseInt(color[1], 16),
     g: parseInt(color[2], 16),
diff --git a/tsconfig.json b/tsconfig.json
index 546ea2a9d12..f8e019a1b8b 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,7 +5,7 @@
 		"moduleResolution": "bundler",
 		"resolveJsonModule": true,
 		"esModuleInterop": true,
-		"strictNullChecks": false,
+		"strictNullChecks": true,
 		"sourceMap": false,
 		"strict": false,
 		"rootDir": "./src",