diff --git a/BizHawk.Emulation/BizHawk.Emulation.csproj b/BizHawk.Emulation/BizHawk.Emulation.csproj
index 9f0bf18b64..bfb2f7c8cc 100644
--- a/BizHawk.Emulation/BizHawk.Emulation.csproj
+++ b/BizHawk.Emulation/BizHawk.Emulation.csproj
@@ -108,6 +108,7 @@
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper107.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper240.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper242.cs" />
+    <Compile Include="Consoles\Nintendo\NES\Boards\Mapper078.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\MMC3_family\DRROM.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\MMC3_family\Mapper095.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\MMC3_family\Mapper206.cs" />
diff --git a/BizHawk.Emulation/Consoles/Nintendo/Docs/compatibility.txt b/BizHawk.Emulation/Consoles/Nintendo/Docs/compatibility.txt
index 80e3547e3e..426145e00a 100644
--- a/BizHawk.Emulation/Consoles/Nintendo/Docs/compatibility.txt
+++ b/BizHawk.Emulation/Consoles/Nintendo/Docs/compatibility.txt
@@ -65,7 +65,7 @@ Open bus and bus conflict emulation is not considered complete or thorough in an
 075	VRC1		Nothing
 076	Misc (J)	Nothing
 077	Misc (J)	Nothing
-078	Misc		Nothing
+078	Misc		Complete
 079	NINA-06		Complete
 080	Misc (J)	Nothing
 082	Misc (J)	Nothing
diff --git a/BizHawk.Emulation/Consoles/Nintendo/NES/Boards/Mapper078.cs b/BizHawk.Emulation/Consoles/Nintendo/NES/Boards/Mapper078.cs
new file mode 100644
index 0000000000..b20fcf6641
--- /dev/null
+++ b/BizHawk.Emulation/Consoles/Nintendo/NES/Boards/Mapper078.cs
@@ -0,0 +1,97 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace BizHawk.Emulation.Consoles.Nintendo
+{
+	class Mapper078 : NES.NESBoardBase 
+	{
+		bool holydiver;
+		int chr;
+		int prg_bank_mask_16k;
+		byte prg_bank_16k;
+		ByteBuffer prg_banks_16k = new ByteBuffer(2);
+
+		public override bool Configure(NES.EDetectionOrigin origin)
+		{
+			switch (Cart.board_type)
+			{
+				case "IREM-HOLYDIVER":
+					holydiver = true;
+					break;
+				case "JALECO-JF-16":
+					holydiver = false;
+					break;
+				default:
+					return false;
+			}
+
+			SetMirrorType(Cart.pad_h, Cart.pad_v);
+			prg_bank_mask_16k = (Cart.prg_size / 16) - 1;
+			prg_banks_16k[1] = 0xFF;
+			return true;
+		}
+
+		public override void Dispose()
+		{
+			prg_banks_16k.Dispose();
+			base.Dispose();
+		}
+
+		public override void SyncState(Serializer ser)
+		{
+			base.SyncState(ser);
+			ser.Sync("chr", ref chr);
+			ser.Sync("prg_bank_mask_16k", ref prg_bank_mask_16k);
+			ser.Sync("prg_bank_16k", ref prg_bank_16k);
+			ser.Sync("prg_banks_16k", ref prg_banks_16k);
+		}
+
+		void SyncPRG()
+		{
+			prg_banks_16k[0] = prg_bank_16k;
+		}
+
+		public override void WritePRG(int addr, byte value)
+		{
+			prg_bank_16k = (byte)(value & 7);
+			SyncPRG();
+
+			if (value.Bit(3))
+			{
+				if (holydiver)
+					SetMirrorType(EMirrorType.Horizontal);
+				else
+					SetMirrorType(EMirrorType.OneScreenA);
+			}
+			else
+			{
+				if (holydiver)
+					SetMirrorType(EMirrorType.Vertical);
+				else
+					SetMirrorType(EMirrorType.OneScreenB);
+			}
+
+			chr = (value >> 4);
+		}
+
+		public override byte ReadPRG(int addr)
+		{
+			int bank_16k = addr >> 14;
+			int ofs = addr & ((1 << 14) - 1);
+			bank_16k = prg_banks_16k[bank_16k];
+			bank_16k &= prg_bank_mask_16k;
+			addr = (bank_16k << 14) | ofs;
+			return ROM[addr];
+		}
+
+		public override byte ReadPPU(int addr)
+		{
+			if (addr < 0x2000)
+				return VROM[(addr & 0x1FFF) + (chr * 0x2000)];
+			else
+				return base.ReadPPU(addr);
+		}
+	}
+}