Bonus Level
To get to a bonus level you must pass Act 1 of each stage with at least 50 rings. 

Chaotic Space bonus level
Collect all Chaos Emeralds before defeating Dr. Robotnik in level 13: Last Utopia to access the Chaotic Space bonus level. In Chaotic Space, Sonic transforms into Super Sonic and battles Robotnik once and for all. 

Defeat Robotnik in “Chaotic Space” bonus level
Press A and stand in the missile’s path when Robotnik fires them at you. Super Sonic will repel the missiles and send them back. 

Recover Chaos Emerald from Dr. Robotnik
When battling Dr. Robotnik in level 13: Last Utopia, hit him seven times. Then target the emerald on his back. After two hits, it will fall off. 

Select level
Press Option at the Sega logo to display all previously played levels. 

Sound test
Collect all seven Chaos Emeralds before completing game to unlock “Sound Test” feature in the options menu. 

Special Stage option
Collect all 96-puzzle pieces, and then assemble six pictures in the Puzzle Room. The Special Stage feature will then become available at the options menu.

Invincibility	
First use the level select code and choose Debug. Highlight Muketi and change it to Yes.

Unlock 6 Chaos Emeralds	
First use the level select code, then go to the Debug screen. Highlight All Clear and change it to Yes.