During game play just pause the game and press the following codes.

Effect	Code
Adds a life bar	B, B, A, A, B, C, C, B.
Create earthquake	B, A, A, B, C, B, B, B.
Halts time	C, B, A, A, C, C, B, A.
Kill enemies	B, A, C, C, A, C, B.
Open doors	B, A, C, A, A, C.
Skip level	C, B, A, A, C, B, A, B.
Slow motion falling	C, A, B, B, B, B.

Note: These codes apply to the European version only.