Sonic 3 & Knuckles: Play As Super Blue:

First use debug mode. Then turn into a ring. Then find a Special Stage Ring. Put yourself in the middle of the ring and press A twice. Finish the stage. Win or lose,you will go back to the regular stage. You should play as 'glitched' up rings. Spawn a TV thing and hit it. When you run super fast, the copys of that character should be blue and the mouth area will be black like a mask.

Note: This will only work with Sonic and Knuckles.