Any time during gameplay, press and hold R2 and press Right, Left, Up to fire a secret freeze weapon.
Invincibility, Quad Damage, and Unlimited Weapons
Enter any of the following cheats during gameplay, but not while the game is paused.
Invincibility: Quickly press L1, R1, L1, R1, Up, Down, Left, Right.
Quad Damage: Quickly press R1, R2, R1, R2, Up, Down, Up, Down.
Unlimited Weapons: Quickly press L1, R1, L1, R1, Up, Down, Left, Down.