While playing sonic 3 and knuckles press Left, Left, Left, Right, Right, Right, Up, Up, Up in the mushroom hill zone, while on one of the pully things. (Just like level select in normal Sonic and Knuckles.) I think you have to do the level select code first.
Description
Effect
Left, Left, Left, Right, Right, Right, Up, Up, Up
Debug mode
Level select when locked onto Sonic 2
Description
Effect
At the title screen hit: Up, Up, Up, Down, Down, Down, Left, Right, Left, Right<p />If entered correctly you should hear a ring sound. Then hold A and press Start
