Te lo pongo en ingles:
Level Select:
At the options menu, put in the following sound tests: 19, 65, 09, and 17.
You'll hear a chime if you did it right. Exit the sound test, and at the title
screen, hold down A and then press Start (B if you're playing on Gamecube).
You will come across the level select screen, which accesses any stage,
including the Death Egg and Special Stages.
Debug Mode:
To enter Debug Mode, play these sounds from the level select screen: 1, 9, 9,
2, 1, 1, 2, 4. Hold A and press Start (B if you're playing on Gamecube)
Easy Chaos Emeralds:
A code I found out myself, but a lot of people know this code anyway. Enter
the Level Select code, and then access the Level Select Screen. Go to Special
Stage and get the emerald. The game should then start at Emerald Hill Zone.
Press Start and then press A, and you'll get back to the title screen. Hold A
and press Start again, go into the level select screen, and go into Special
Stage. Get that Chaos Emerald, and notice how you have two. Just repeat the
process.
More Continues:
Enter level select. Then from the Options screen, play the following songs in
this order: 1, 1, 2, 4. Highlight Player Select and press Start.
Play at Night:
To play at night, enter the Debug code, then hold C and press Start to begin a
level (or whichever button is C on the Gamecube controller).
Super Sonic:
To become Super Sonic without getting all the Chaos Emeralds, first enter the
level select. At the level select menu, go to sound test, and play the
following songs in this order: 2, 1, 4, 6. You'll hear a sound like you would
when you win a Chaos Emerald. Next, go to any level and press start. To
become Super Sonic, get 50 rings and jump.