diff --git a/BizHawk.Emulation/BizHawk.Emulation.csproj b/BizHawk.Emulation/BizHawk.Emulation.csproj
index 665d27efe0..e07f5d693b 100644
--- a/BizHawk.Emulation/BizHawk.Emulation.csproj
+++ b/BizHawk.Emulation/BizHawk.Emulation.csproj
@@ -161,6 +161,7 @@
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper227.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper230.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper231.cs" />
+    <Compile Include="Consoles\Nintendo\NES\Boards\Mapper233.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper240.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper241.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper242.cs" />
diff --git a/BizHawk.Emulation/Consoles/Nintendo/NES/Boards/Mapper233.cs b/BizHawk.Emulation/Consoles/Nintendo/NES/Boards/Mapper233.cs
new file mode 100644
index 0000000000..171a18b99a
--- /dev/null
+++ b/BizHawk.Emulation/Consoles/Nintendo/NES/Boards/Mapper233.cs
@@ -0,0 +1,127 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace BizHawk.Emulation.Consoles.Nintendo
+{
+	class Mapper233 : NES.NESBoardBase
+	{
+		/*
+		Here are Disch's original notes:  
+		========================
+		=  Mapper 233          =
+		========================
+
+
+		Example Game:
+		--------------------------
+		???? "42-in-1"  ????
+
+
+		Notes:
+		---------------------------
+		Sources report this mapper as "42-in-1" with description layed out below.  I did not test this,
+		since I could not find a copy of the ROM in question.  The only ROM I have that's marked as
+		233 is "Unknown Multicart 1", and it does *not* follow the description in this doc at all.
+
+		There is a "Super 42-in-1"... but that is mapper 226.  226, by the way, is strikingly similar
+		to the below description.  I wonder if below description really applies to 233?
+
+
+
+		Registers:
+		---------------------------
+
+		$8000-FFFF:  [MMOP PPPP]
+		M = Mirroring
+		O = PRG Mode
+		P = PRG Page
+
+
+		PRG Setup:
+		---------------------------
+
+			$8000   $A000   $C000   $E000  
+			+-------------------------------+
+		PRG Mode 0: |            <$8000>            |
+			+-------------------------------+
+		PRG Mode 1: |     $8000     |     $8000     |
+			+---------------+---------------+
+
+
+		Mirroring:
+		---------------------------
+
+		'M' mirroring bits:
+		%00 = See below
+		%01 = Vert
+		%10 = Horz
+		%11 = 1ScB
+
+
+		Mode %00 (almost, but not quite 1ScA):
+		[  NTA  ][  NTA  ]
+		[  NTA  ][  NTB  ]
+		*/
+
+		public int prg_page;
+		public bool prg_mode;
+
+		public override bool Configure(NES.EDetectionOrigin origin)
+		{
+			switch (Cart.board_type)
+			{
+				case "MAPPER233":
+					break;
+				default:
+					return false;
+			}
+
+			prg_mode = false;
+			return true;
+		}
+
+		public override void SyncState(Serializer ser)
+		{
+			ser.Sync("prg_page", ref prg_page);
+			ser.Sync("prg_mode", ref prg_mode);
+			base.SyncState(ser);
+		}
+
+		public override void WritePRG(int addr, byte value)
+		{
+			prg_page = value & 0x1F;
+			prg_mode = value.Bit(5);
+
+			int mirror = value >> 6;
+			switch (mirror)
+			{
+				case 0:
+					SetMirroring(0, 0, 0, 1);
+					break;
+				case 1:
+					SetMirrorType(EMirrorType.Vertical);
+					break;
+				case 2:
+					SetMirrorType(EMirrorType.Horizontal);
+					break;
+				case 3:
+					SetMirrorType(EMirrorType.OneScreenB);
+					break;
+			}
+		}
+
+		public override byte ReadPRG(int addr)
+		{
+			if (prg_mode == false)
+			{
+				return ROM[((prg_page >> 1) * 0x8000) + addr];
+			}
+			else
+			{
+				return ROM[(prg_page * 0x4000) + (addr & 0x03FFF)];
+			}
+		}
+	}
+}