I have a list of characters who might star in this game. Yes, I have no life and I just sit at my computer desk coming up with this stuff. I love crossovers sometimes.
Mario-Solid Snake (obvious reasons)
Luigi-Liquid Snake (obvious reasons)
Wario-Solidus Snake (he can buff himself out, and he's sort of related to Mario)
Link-Raiden (the sword, the looks, the everything)
Sonic-Ocelot (a quick draw, and he's Mario's rival from the old days)
Pikachu (male)-Otacon (electrical technician)
Pikachu (female)-Emma (if Otacon is a Pikachu, then Emma has to be one too)
Yoshi-Metal Gear Ray (Ray sort of looks like a horrifically mutated Yoshi)
Samus-Fortune (it's the gun)
Bomberman-Fatman (do I really need to explain this one?)
Castlevania Dracula-Vamp (again, must I explain?)
Piccolo-Peter Stillman (go to YouTube and watch one of WeeklyTubeShow's videos and you'll see why I picked Piccolo)