You bet. I even did an article here on one called Somari, a hack of Sonic the Hedgehog with Mario in Sonic's place for NES. Check it out sometime. I've also seen something called Afro Mario Bros. lol.

sonic jam 6, my, what crappy graphics... and sonic goes directly down when you let go of the jump button. and when you get out of the pipe in level 1-2, why does it send you right to level 1-3? seemed like a fun hack to play for the first few minutes. have you guys also tried sonic crackers? it seemed ok, but the levels felt endless and i kept getting a time out. i gave pocket monsters for the nes a try, pretty bizarre