During the gameplay press the following:
Unlimited ammunition: R, L, A, Up, Down, B, X, R(2)
All weapons: R, L, Up, Down, A, Up, X, A
Level skip: R, L, Up, Down, A, X, click Left Analog-stick, press B, A, B, A
Level select: R, L, Up, Down, X, Y, B
Nailgun mode: R, L, Up, Down A, White(2)
God mode: R, L, Up, Down, A, R, L, Black, White
Full heal: R, L, Up, Down, A, Up, Down
Toggle gravity: R, L, Up, Down, A, L(2)
Megaforce mode: R, L, Up, Down, A, R(2)