Get a certain number of skill points to unlock each of the cheats:

Effect - Code

Big Head A.I. - 20 Skill Points
Big Head Ratchet & Clank - 5 Skill Points
Mirror Worlds - 30 Skill Points
Secret Agent Clank - 15 Skill Points
Ships to Ducks - 25 Skill Points
Time Freeze - 10 Skill Points
Wrench Replacement - Enter code from Demo