Codes

Effect	Code
Big Head Mode	X, A, Y, B (3x), Up (5x) (on controller D, on Press Start screen after beating game on Easy)
Mirror Mode	L, Left, L, Right, L, Down, L, Up, R, Left, R, Right, R, Down, R, Up (on controller D, on Press Start screen after beating game
Random Mode	B, Left, X, Y, X, Y, B, A, B, A, Right, Left, Right, Left (on controller D, on Press Start screen after beating game on Hard)

Secrets

Play as Janet
Start a new game, then hold Start at the mission select until the mission begins.
Power Up Weapons
Pause game play and reload to power-up your weapon to one of the special guns. It only lasts for one round of ammo.