Get 750 on the Shooting Gallery and The Brains That Ate California for two Gold Coins and two episodes of Rocket Power.
Cheat mode
Go to the options menu and choose "Cheats". Answer the series of seven questions with the following to unlock the entire game:
1. Squid
2. Conroy
3. Tito Makani
4. Maurice
5. Ocean Shores
6. Otto
7. Eddie:Prince of the Netherworld
Play as Eddie
Collect 60 Gold Coins to unlock Eddie.
Play as Eric Golem Jr.
Collect 50 Gold Coins to unlock Eric Golem Jr.
Play as Lars
Collect 40 Gold Coins to unlock Lars.
Play as Pi
Collect 20 Gold Coins to unlock Pi.
Play as Spurtz
Collect 30 Gold Coins to unlock Spurtz, Pi's friend.
Unlock All Levels
To unlock all of the levels, go to the Cheats screen via the Options menu. Answer the multiple choice questions: c, a, b, c, b, c, c. All levels will then be available from the Zine screen.