This is an actual cartridge. The cartridge has extra hardware inside of it to make this kind of game possible to run on a Gameboy. The co-processor is an ARM Cortex-M0 from NXP called KE04. The creator chose it because it is quite small, has a pin pitch that can comfortably be hand soldered. And is one of the few that still runs on 5V.

Someone has remade Wolfenstein 3D for the Gameboy Color

That’s a really impressive technical achievement of what you could do on a 2D-only console. And have pseudo-3D capabilities. Really awesome port. If only this would have been an actual port done two decades ago. Then it would have achieved a lot of critical acclaim. Calling it the Resident Evil 2 of the Gameboy Color.

There’s still a chance to get MIDI (albeit a very frugal implementation) output (maybe on the link port) in order to connect MIDI hardware to get some music. Maybe there could be a different build with less content in order to accommodate the music file space?

The GB/GBC can address larger ROMs by swapping virtual memory tables. It should probably be possible to use a ROM larger than 128KB doing this. The developer is currently using 123Kb out of the 128Kb ROM space so he’s starting to reach the limit on what will fit.

Wolfenstein 3D is a first-person shooter video game developed by id Software and published by Apogee Software and FormGen. Originally released on May 5, 1992, for MS-DOS, the game was inspired by the Muse Software video games Castle Wolfenstein and Beyond Castle Wolfenstein. In the game, the player assumes the role of Allied spy William “B.J.” Blazkowicz during World War II as he escapes from the Nazi German prison Castle Wolfenstein and carries out a series of crucial missions against the Nazis.