Sonic The Hedgehog 2

Level select (US / Jap version):
Note: This code has sensitive timing. Tails will blink his eyes once, then two more times in quick succession. Hold Down/Left + 1 + 2 at the title screen and wait until Tail blinks for the third time. Press Start at exactly that moment, while Tails' eyes are closed. A sound will confirm correct code entry. Use Up or Down to select a level and press 2 to begin game play. Alternatively, hold Down/Left + 1 + 2 during the introduction sequence and keep them held as the title screen is displayed. Release the buttons after the sound of the bells are heard. Press Start to enter the level selection screen. Information in this section was contributed by Trevor Smith.

Level select (European version):
Enter the sound test screen and play tracks 19, 65, 9, and 17 (in order). Press Start to exit the screen. Wait until Sonic and Tails give a "thumbs up" and press 1 + Start, Start.

Level passwords (European version):

Level  Password
2  EAGF
3  CHFA
Bonus  (none)
5  DGBC
6  HBGA
7  FBHE
Bonus  (none)
9  BFCH