Sonic 2 Hacking Guide
Genecyst Savestate - Cheats

It's not hard at all to enable cheats. This will allow you to play the game to it's fullest without ever needing to use cheat codes.

012281 (FE09) - Debug active (01 to activate)
012448 (FFD0) - Level select (01 to enable)
012449 (FFD1) - Slow motion (01 to enable)
01244A (FFD2) - Debug mode (01 to enable)
01244B (FFD3) - Unknown cheat (01 to enable)
012472 (FFFA) - Debug mode presently enabled (01 to enable)