Unlock Skins
Enter the following codes at the Extras menu:
2839 - Daphne's skin.
3726 - Shaggy's skin.
3726 - Scooby's skin.
4826 - Freddy's skin.
6588 - Velma's skin.
Unlock Bonuses
Enter the following codes at the Extras menu:
6767 - Unlimited Scooby Snacks.
2129 - Unlock all Levels.