Pick level:
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At the Main menu press the following sequence:
Triangle,Circle,Triangle,Square,Triangle
Circle,L1 + R1
Get All Costumes -
At the Main menu press the following sequence:
Triangle,Circle,Triangle,Square,Square
Square,L1 + L2
Unlock Cerebro Files -
At the Main menu press the following sequence:
Triangle,Circle,Triangle,Square,Square
Square,R1 + R2