A hack of Clayfighter, any one in the series. Some palette editing of Blob, or maybe even the muscle guy, whatever his name was, to make them brown. Remove the rest of the characters. Voila, you have Street Farter 3: Turd Strike!

Next is more of a vague idea, but I'm thinking Contra, or maybe even Cannon Fodder (snes game from europe). The shooting sounds changed for bodily noises, projectiles changed to some brown stuff, and perhaps some other clever changes, and you have Tour of Doody.

I think these would be awesome romhacks.

You can't be serious. How old are you?  :huh: