diff --git a/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj b/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
index 8c38a41d73..16404afba4 100644
--- a/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
+++ b/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
@@ -340,6 +340,7 @@
     <Compile Include="Consoles\Nintendo\NES\Boards\BANDAI_74_161_161_32.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\BxROM.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Camerica.cs" />
+    <Compile Include="Consoles\Nintendo\NES\Boards\CoolBoy.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\DatachBarcode.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Farid-UNROM-8-in-1.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\FS304.cs" />
diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/CoolBoy.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/CoolBoy.cs
new file mode 100644
index 0000000000..b3cb891892
--- /dev/null
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/CoolBoy.cs
@@ -0,0 +1,117 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+using BizHawk.Common;
+using BizHawk.Common.NumberExtensions;
+
+namespace BizHawk.Emulation.Cores.Nintendo.NES
+{
+	public sealed class CoolBoy : MMC3Board_Base
+	{
+		// eldritch horror pirate multicart
+		// 32MB prg rom, no prg ram, no chr rom, 128KB chr ram
+
+		// behavior directly from fceu-mm
+
+		// this could be broken down into more sensibly named variables
+		byte[] exp = new byte[4];
+
+		public override bool Configure(NES.EDetectionOrigin origin)
+		{
+			switch (Cart.board_type)
+			{
+				case "UNIF_COOLBOY":
+					AssertChr(0);
+					break;
+				default:
+					return false;
+			}
+
+			Cart.vram_size = 128;
+			Cart.wram_size = 0;
+
+			BaseSetup();
+
+			// normally base mmc3 sets this right, but it has a hardcoded assumption
+			// that no chr rom => 8K of chr ram, not 128K.  i'd change the base class,
+			// but not sure if that would break something else
+			chr_mask = 127;
+
+			return true;
+		}
+
+		public override void WriteWRAM(int addr, byte value)
+		{
+			if (addr < 0x1000)
+			{
+				if (!exp[3].Bit(7))
+				{
+					exp[addr & 3] = value;
+				}
+			}
+		}
+
+		protected override int Get_PRGBank_8K(int addr)
+		{
+			int mask = 0, shift = 0;
+			int baseaddr = exp[0] & 0x07 | (exp[1] & 0x10) >> 1 | (exp[1] & 0x0c) << 2 | (exp[0] & 0x30) << 2;
+
+			switch (exp[0] & 0xc0)
+			{
+				case 0x00:
+					baseaddr >>= 2;
+					mask = 0x3f;
+					shift = 6;
+					break;
+				case 0x80:
+					baseaddr >>= 1;
+					mask = 0x1f;
+					shift = 5;
+					break;
+				case 0xc0:
+					shift = 4;
+					if (exp[3].Bit(4))
+					{
+						mask = 1 | exp[1] & 2;
+					}
+					else
+					{
+						mask = 0xf;
+					}
+					break;
+				case 0x40:
+					// ??
+					throw new InvalidOperationException();
+			}
+
+			int v = base.Get_PRGBank_8K(addr);
+
+			int ret = baseaddr << shift | v & mask;
+			if (exp[3].Bit(0))
+			{
+				ret |= exp[3] & (0x0e ^ exp[1] & 2);
+			}
+			return ret;
+		}
+
+		protected override int Get_CHRBank_1K(int addr)
+		{
+			if (exp[3].Bit(4))
+			{
+				return (exp[2] & 15) << 3 | addr >> 10 & 7;
+			}
+			else
+			{
+				return base.Get_CHRBank_1K(addr);
+			}
+		}
+
+		public override void SyncState(Serializer ser)
+		{
+			base.SyncState(ser);
+			ser.Sync("exp", ref exp, false);
+		}
+	}
+}