Misc Cheats

Extra Ammo
To get extra ammunition, pause the game and hold down L1 + L2 for 10 seconds. While holding these buttons, press Triangle, LEFT, LEFT, LEFT, O, Triangle, Down. From here on you can refill your ammo by pausing the game and selecting the ammo option that appears.
Healing
To heal yourself, pause the game and hold down L1 + L2 for 10 seconds. Continue to hold those buttons and press DOWN, RIGHT, LEFT, Triangle, RIGHT, DOWN. From here on you can heal yourself by pausing the game and selecting the Health Option that appears.
Level Skip
Pause the game and hold L1 + L2 for 10 seconds. While holding those buttons press LEFT, Triangle, X, RIGHT, Circle, Triangle, DOWN.
Play as Fwank
At the Charcter Select Screen highlight Mamma and press L1, O, R1, DOWN, DOWN, R1, O, L1, L1. A Red Balloon should appear over Sister Magpie. Highlight her slot and Fwank should be there now.
Weapon Power Up
To boost your weapon up, pause the game and hold L1 + L2 for 10 seconds. While holding those buttons, press LEFT, UP, X, O. From here, you can power up by pausing the game and selecting the Power Option that appears.