LEVEL SELECT

After the "SEGA" call, start a new game as any character. While in Angle Island Act 1, grab any swinging vine and, while swinging back and forth, enter left, left, left, right, right, right, up, up, up. You should hear a chime like you just grabbed a ring. Now, pause the game and push A. Back at the Main Menu, push up to reveal a secret option: "SOUND TEST". You will see all the zones and a sound test option hear. The small number under the Angle Island level means witch character your playing as. 00 Means Sonic and Tails. 01 Means Sonic alone. 02 Means Tails alone. And 03 means Knuckles.

DEBUG MODE

After entering the LEVEL SELECT code, go to Mushroom Hill zone and grab and of the pulley's found there ( those tall things that you need to climb by pushing down ). While hanging on one, enter left, left, left, right, right, right, up, up, up. Another ring chime will sound. Then, pause and press A. Go back to Level Select and choose the level and character you want to play as. Then, hold A and push START. Note: unlike the debug modes from Sonic 1 and Sonic 2, this time around, you have the option to reverse gravity.

Debug mode controlls:

Arrows: move.
A: reverse gravity as character/Change item in debug mode.
B: enter/exit debug mode.
C: place item/jump as character.a

Dude this isnt the cheat for sonic and knukles and sonic2.This is the cheat for sonic 3 and knuckles