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Platform: Game Gear

Codes For Sonic Labyrinth
Sonic Labyrinth

Level select:
Press Up(2), Right(3), Down(6), Left(9), Start at the title screen. Select the "Config" option and use Left or Right to choose a starting level.

Bonus level:
Enter the cannon in zone 2-3 and press 1 + 2 + Right. Turn on the switch to open the door to the bonus level.