Sonic Advance 3

GBA

Secret Stage:
Beat every special stage, then go to the main menu and press Up, L, Down, R, Right, Left.

Play as Knuckles:
Beat the Sunset Hill Zone Acts.

Play as Amy:
Beat the Toy Kingdom Zone Acts.

Play as Cream:
Beat the Cyber Track Zone Acts.

Thanks to Revolution readers Dingledong and Mr. Larry!