Sonic The Hedgehog 2

ALL Chaos Emeralds:
Enable the 'Level Select' code and then play songs '04', '01', '02', and '06' in order at the 'Sound Test' menu.

Hidden options:
First use the level select cheat.
Next play sound 00 a three times, a new menu will apper to allow you to change things like the player character (Knuckles and Tails can be choosen), item set such as s2 items, s3&k items,s2 random, s3 random, and you can also toggle the air cap and toggle flight.

Level Select and Sound Test:
First start a no save game.
Next when the Sega logo appears tap the letters S-E-G-A in that order.
Now hold two fingers on the screen and wait until the level select/sound test screen appears, than you can take your fingers off the screen.