Sonic 2

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 14 continues.

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.

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.

To get Ashura, you must enter the level select and debug code. Then you must choose one of the emerald hill zone levels because the code only works in emerald hill zone (1 or 2.) When you start the level press B, you will be a ring,then press a four times,you will be four rings in a row going up or down,you then hold c and right for about 5 seconds,then you go back to the begining, keep pressing a until your the top of a waterfall. You may not see yourself but you're there. Now do the same thing as before, hold c and right for about five seconds. Then press b and you'll be Ashrua, or, green Sonic.

For all those who like to play honest instead of cheating all those Chaos Emeralds together, there's an alternate - yet simple - way to become Super Sonic in Emerald Hill Zone 1. It involves some serious work, however:1. Complete the special stages as you would usually do and collect as many emeralds as you want.
2. Press RESET.
3. Start a new game USING THE OPTIONS MENU! This is crucial! Otherwise your emeralds are gone for good!
4. Continue collecting the emeralds, if you don't have them all, yet and repeat point two and three until you got them all.If you did everything correctly, after your last reset you should have all the emeralds from the very beginning and without using any code ever thus making Super Sonic available from the very beginning.This has been tested and confirmed with the PAL version of Sonic 2 playing on a PAL Megadrive II.

Press up, up, up, down, down, down, up at the title screen

First enter the level select code (Mentioned above).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.

First activate and go to the Stage Select. Play the tracks in Sound Test with button B in this order:
01 09 09 04 01 00 01 08
This enables the Debug code, you should hear a ring chime if the code is entered correctly. start the selected level with A+start.
To get all 7 Chaos Emeralds, input this code the same way:
01 06 07 07 07 02 01 06
You should hear the Emerald chime. note: this code may not work without the Debug code

First, head to the Options menu from the title screen, and then into the Sound Select menu from there. Play the following sounds in this order:

19
65
09
17

After that, press the C button and then Start. You will be taken back to the title screen. Now, when you see Sonic and Tails (Mils) appear on the screen, press and hold A and press Start while holding A to be taken to the Level Select menu.

From this menu, enter the Sound Test feature, and play the following sounds in this order:

04
01
02
06

If done correctly, you will hear a familiar tune, confirming the Super Sonic code was done correctly. Exit this menu and start the game as normal. Once you collect a minumu of 50 coins in any level, Jump (Press A) to activate the Super Sonic code.

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.