Cheat List
Input these during the Credits Movie in the Main Menu section
Invincible Mode: X + Z + R
All Upgrades: X + Y + L
Unlock All levels: X + Z + Y
These cheats have been verified to only show up and not actually carry over into the actual gameplay session. The exceptions are Unlock Levels, which unlock all stages with a score of zero and Invincibility, which applies itself quite well to the Co-Op mode.