Secret characters
Go into Blast, then press [Down] [Down] [Right] [Left] [Right] [Up] [Left] [Down] [Right]. Then, go to the character selection screen. Cosmo, Wanda, Patrick, and Carl Wheezer will now be unlocked.
Unlock the Bungi games
Highlight the Bungi game at the bottom of the game selection screen, then [Up], [Up], [Down], [Down], [Left], [Right].
Unlock the Clam games
Go to Blast, then press [Up], [Up], [Down], [Down], [Left], [Right] to unlock the levels for the clam games.