I suspect pretty hard, but would it be feasible? Some tools already exist, including a map editor and a compiler, would it be possible to create an environment in Unity that would ultimately output a ROM? Is this too ambitious?
Anybody has any experience with that kind of stuff?
Well I wouldnât think so if there is no exported for it lol.
Of course, you would have to make an exporter. Thatâs the hard part.
I think youâve just answered your own question 
How exactly would you use Unity? If you mean monodevelop, Visual studio is a better option and QT is my personal option (small C editor with auto-complete, woo!). If you mean for putting maps together, I guess you could use unity to design a level visually and then export the scene as plain text. You would probably be better off making a level editor in C.
Yeah, I think the effort that you would need to put in to Unity to make a Game Boy game is gargantuan. Unity doesnât even do true 2d; it uses 3d quads with âspriteâ materials. Making a GB game with Unity is boarder line absurd. Just look around for existing software to make GB roms rather than repurpose something that was never intended for such a use.
Itâs possible but a huge effort. Iâve been developing for the GBA recently and it would be far easier just to make the game in raw C or ASM (On the GBA thereâs also BASIC and some others IIRC)
Itâs not even remotely possible. For one, we are talking about a system that uses EIGHT KILOBYTES of ram. Make a standalone build that just prints hello world and see how much memory it uses. Iâll be damned if the base engine doesnât use at least a few megs.
The question was if Unity could output a GB game, not if it could run on it.
Huh? Some how the nuance of using a game engine to make a game that wonât use that engine eluded me. I canât even imagine the editor being of any use for this situation either when you need different compilers and an emulator to test it. At that point, there is no reason to use unity when everything youâre doing requires custom tools.
Why would make a gameboy game when it canât run on it? Kinda a pointless question haha
Here you go OP.
It wouldnât make sense but could be done.
make ipad / android games with the art style of gameboy, i guess⌠but i get its interesting just to know whats possible
google âtwo brothers gameâ
Iâd rather program in C and compile to a gb rom than use Unity as an engine to drive game logic.
But, you could use Unity to make a tile editor, then export the indexes to a c file.
All these wonderful responses aside, why would one wish to do this? Is Gameboy making a comeback?
Iâve been making a GBA game for fun, it gives a good understanding of limits and optimization. It might become my business card as well. I canât imagine programming on the original though as itâs to limiting. I want to make a SNES game next, or maybe Atari jaguar.
I honestly donât think Unity will be adding a âGameboyâ option to the Build Settings. 
Should we support VirtualBoy too? Or what about the NeoGeo?
Haha NeoGeo
GB probably has a larger market than Linux. 