Invincibility:
Press Start to pause game play, then quickly press Down, Left, Up, Right, L, A, X,
Left, R, B, Y, Up, L, A, Down.

All weapons:
Press Start to pause game play then quickly press Up, Right, Left, Down, B, L, R,
A, Right, X, B, Left, R, Y, Up.

Full pause screen:
Pause game play, then press X + Y.