Sonic Adventure DX - Platform: Gamecube

In-game reset:
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Hold Start + A + B + X for a few seconds during game play.

Sonic Chaos: Level select:
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Press Up(4), Right, Left, Right, Left, Start when 
"Press Start" appears at the Sonic Chaos title screen.

Sonic Labyrinth: Level select:
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Press Up(2), Right(3), Down(6), Left(9) when 
"Press Start Button" appears at the Sonic Labyrinth title screen.

Sonic Spinball: Level select:
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Enter the "Sound Test" option for Sonic Spinball. 
Then, play the following songs in order: 0, 2, 1, 5, 6, 6.

Sonic Spinball: Faster background music:
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Enter the "Sound Test" option for Sonic Spinball. 
Then, play the following songs in order: 0, 4, 2, 5, 5, 7.

Sonic Spinball: Disable gravity:
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Enter the "Sound Test" option for Sonic Spinball. 
Then, play the following songs in order: 0, 9, 0, 1, 6, 8.

Sonic Spinball: Zoomed in view:
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Enter the "Sound Test" option for Sonic Spinball. 
Then, play the following songs in order: 0, 2, 1, 1, 6, 6.

Sonic The Hedgehog 2: Level select:
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At the Sonic The Hedgehog 2 title screen, 
Tails will blink his eyes (first once, then two times quickly). 
While holding Down/Left + A + B, tap Start just when his eye 
shuts on the second blink of the double-blink.