Level select
At the title screen, press Up, Down, Left, Right. If you entered the code correctly, you will hear a chime. Hold X + Start to begin a game.

All Chaos Emeralds
Enable the "Level select" code, then choose the "Bonus level" option on the level selection screen. Obtain the Chaos Emerald, reset the game, and repeat the process until all of them are in your possession. Allow the game to continue after obtaining the last Chaos Emerald to start in the Green Hill Zone.

Debug mode
At the title screen, press Up, A, Down, A, Left, A, Right, A, Start, then hold X. Continue to hold X until the game begins. Screen coordinates will appear instead of a score and the number of objects displayed will appear instead of the time remaining. Use one of the following controller actions to enable the corresponding debug code:

Object transformation
Press A during the game to change Sonic into a game object. Press X to change into a new object. Press B to place an object on the screen. Press A again to revert back to Sonic. Note: The type of object that may be selectable will vary from level to level.

Invincibility
Sonic is, by default, invincible in debug mode.

Slow-motion
Pause the game and hold A.

Restart
Pause the game and press X.

Frame advance
Pause the game and press B.

Control ending sequence
Enable the "Debug mode" code. Press A when Sonic is running with the animals at the end, then turn back into Sonic. You can now control yourself.

Crazy Sonic
Hold X + A + B during demonstration mode to force Sonic to run into objects and act strangely. Note: This may also be done during the ending sequence after completing the Final Zone.

Infinite lives
Collect the extra life at the very bottom of Green Hill Zone - Act 3. Accumulate 100 rings to obtain another extra life. Collect a third extra life located at the top of the loop-the-loop. Intentionally lose a life and repeat the process.

Bonus points
Complete Green Hill Zone 1-1 or 1-2 in 29 seconds or less to receive 50,000 bonus points