Sonic the Hedgehog 2 Command codes

All cheats
Main cheats:
19, 65, 9, 17 Level select (hold A and press start at title to enter Level Select).
1, 1, 2, 4 Extra Continues.
4, 1, 2, 6 All Emeralds (Need 50 Rings to turn into Super Sonic).
1, 9, 9, 2, 1, 1, 2, 4 Debug mode.

Note: Enter these in Sound Test from the options menu, enter each one by pressing C button, a ring sound will confirm correct entry, except for Debug mode if done correctly.

Debug mode controls:
Up,Down,Left or Right to move
A to change item
B to enter/exit debug
C to place current selected item

Options cheats:

7B Speeds up in-game music by 2X
7C Returns in-game music to 1X
7D Stops current music/SFX
7E Mutes Audio even in-game
7F Unmutes Audio

Only 7B-7D only works in options, but not in-game.
7E works in both in-game and Options.

Up, Up, Up, Down, Down, Down, Up change Tails name to Miles in options, enter at title screen.

Get Extra Lives per act with debug:
Enter debug mode code and start with Sonic and Tails, change Sonic into a ring, now have the ring over next to tails and keep pressing C button.

Note: Once you collect 200 rings it stops working, until you move on to the next act, get hit by an enemy or you end up dying in that current act.