Sonic #1
Debug Mode:Go to the Sonic 1 title screen and press Up, X, Down, X, Left, X, Right, Up, X, Down, X, Left, X, Right, X. Now HOLD B and press Start. Now when the game starts press A to go to debug mode
Pick Level & Sound Test:
Go to the Sonic 1 title screen and press Up, Down, Left, Right. Now HOLD B to pick a level & get sound test
Sonic #2
Pick level:Go to the Sonic 2 Sound Test screen and play sounds 19, 65, 09, 17. Now HOLD X and press START. Now on the title screen HOLD B and press START
Debug Mode:
Go to the Sonic 2 Sound Test screen and play sounds 01, 09, 09, 02, 01, 01, 02, 04. Now at the sound test screen HOLD B and pick a level and Start
Be Super Sonic:
After doing the Pick Level code above go to the Sound test screen and play sounds 04, 01, 02, 06. Now collect 50 rings and jump to be Super Sonic
Sonic #3
Pick Level:As you hear SEGA spoken BUT before the main menu appears press Up, Up, Down, Up, Up,Up. Then at the title screen press UP to get Stage select and Sound Test
Debug Mode:
Go to the Stage Select screen and HOLD B and pick a level and start
Get Extra Stage:
After doing the Pick Level code above go to the Sound test screen and play sounds 01, 03, 05, 07. Highlight the Special Stage 2 and HOLD B and press START