This code only works for Sonic. First, do the Level Select cheat. In the Level Select menu, go to Sound Test and hear the sounds 04, 01, 02, 06 in this order. If done correctly, you'll hear a Chao Emerald sound effect. Now, select any stage from this menu and not only you'll be able to turn into Super Sonic with 50 rings but also you'll get Sonic's second ending after beating Death Egg Zone.
Alternate Debug
Enter at soundtest ''19, 65, 09, 17'', then press A + start, then when sonic and tails pop up, press A + Start to go to the level select screen. On the sound test area, enter ''01 09 09 02 01 01 02 04'' and then press A + Start. This is an alternate debug to the others.
Change Tails' name to Miles in game above lives
At the Title screen, press Up, Up, Up, Down, Down, Down, Up.
Debug Mode
First enter the level select code. Now,go to sound test option,and play the following tunes - 1, 9, 9, 2, 1, 1, 2, 4 - It should make a ring sound when track 4 is played to signify you've entered it correctly, now select the stage you want to go to, and press start while holding A until the stage starts,and you'll have debug activated.Here are the controls.
B-Turn Debug on/off
A-Switch object
C-Put down object selected
Pressing A while the game is paused will cause the game to reset.
Fourteen Continues
Go to the sound test (not the one on the level select) and put in 19, 65, 09, 17, 01, 01, 02, 04 (press A after each one). There won't be a confirmation sound. Start the game by pressing Start on the first option (character select) and you should have fourteen continues.
Get Super Sonic on Emerald Hill
First, you enter the stage select code, shown above. Then you go into the Special Stage in the stage select menu. Every time you finish the special stage press reset and go back to the special stage. Keep doing this until you get the sixth emerald. Then you don't press reset. It will just zap you with your six emeralds into emerald hill. Get the last emerald on Emerald Hill get 50 rings and jump to be super sonic. Be careful to not run out of rings or else you will change into Sonic again. The rings start dissapearing when you are Super sonic.
Night Mode
Activate level select and hold C while selecting a stage to darken the level. The effect wears off when you die or when you beat the level.
Pseudo Super Sonic
In Oil Ocean Zone, if you manage to take a hit and end up landing in one of those green-and-gold checkered cannons, you'll fall right out, but you'll be moving at twice your normal speed as well as jumping twice your normal height(with twice as much gravity). A good place for doing this would be in Oil Ocean Zone, Act 2, near the first set of pop-tops and cannons. Just jump into the semi-hidden bed of spikes on the right and land in the cannon.
Note: Moving at twice normal velocity can often get you stuck in a wall. Also, this wears off if you Super Spin Dash or Spin Dash. It also only lasts for that Act.
Silent Mode
Go to the Options menu from the title screen, and then while there go to Sound Select and play sound number 7E. You'll notice that the game music had stopped. Now start the game and you'll be able to play the game without any music and sounds.
Slow Motion
Weird trick, but you can play this game in slow motion. First, enter the level select code, found somewhere in the list of all other codes. Then start your game in any level. When you start, press pause. Then hold down B button and try to do anything with Sonic. The game will play in slow motion as long as you hold down the B button.
Super Tails
Normally, when you turn into super sonic you lose tails behind you all the time. Well, after you put in the debug cheat and have started a level (preferrably Emerald Hill), turn yourself into a box and place it somewhere on the floor while you are super sonic. It should be a switch places box. Hit it and you will see tails will have a permanent invincible circle around him. He will stay like this through the whole level, he will keep up with super sonic or even out run him. A very fun glitch for two players.
Unlimited Lives
First, enable the level select cheat and the debug mode which are available here. For this to work, you must choose Sonic and Tails as the players.
After entering the codes, choose any stage from the level select menu (preferrably stage 1) .
As soon as you can move Sonic, hold down, and press C(don't let go of down on the D-pad). This will activate Sonic's spin; Tails will copy the Sonic spin also.
Press the B button and Sonic will become the Debug cursor.(Tails will be locked in the sonic spin move).
Press A until you(the debug cursor), displays an enemy sprite, like the monkey or that bee robot. Now that the debug cursor displays an enemy sprite, move the debug cursor to where Tails is, and repeatedly tap C.
This will produce enemies where Tails is, and since Tails is locked in the sonic spin move, he will destroy the enemies. As Tails destroys enemies in this position, press C more until the score for destroying an enemy increases from 100 to 8000 to a 1up. Once you have enough 1ups, press B again to revert to Sonic.