Debug Mode
At the sound test screen (you need to unlock it first) enter the following tracks: PCM 12 DA 11. After seeing a picture of Tails, start a new game, holding down A + Start. It is okay to skip the intro. Just ensure you are holding down [A] + [Start] by the time the zone loads up. You will know if it worked if you see your X and Y coordinates ticking on the upper right hand of the screen.
[B] - Debug mode.
[A] - Cycles object (while in debug).
[X] - Places object (while in debug).
Achievements will be disabled and Zone/Act times will not be recorded while Debug Mode is active.
Unlock Extras Menu
D.A. Garden - Beat all the normal stages with a total time of 25:00'00 or better.
Sound Test - Beat all the special stages with a total time of 5:00'00 or better.
Stage Select - Beat all the special stages with a total time of 4:00'00 or better.
Visual Mode - Beat all the normal stages with a total time of 25:00'00 or better.
Automatic Game Over
If you leave Sonic standing still for 3 minutes, he will grow impatient and yell at the player. He will then jump off the stage, causing an automatic "Game Over".