Level skip:
At the Main Menu, press C-Up, C-Down, C-Left, C-Right, C-Right. Now during play press press Start, C-Up, C-Down to skip levels.

Level Select:
Beat the first level. Save the game, then exit to the Main Menu and go to Load Game. When asked to 'enter rumble pak,' hold L + B and press A. Now you should have access to any level.

Become a Car:
In Practice mode, pick up a car and fly with it through all the rings around the Lexcorp building. Once you fly though the last red ring, the game should glitch, and you should end up in the car!

GameShark Codes

Infinite Health	            8122cdd442c8
Infinite Freezing Breath    8122cde842c8
Infinite Running Boosts     8122cddc42c8
Infinite Laser Eye          8122cde442c8
Infinite X-Ray Vision       8122cde042c8
Fly Through 1st & Last Ring Only To Complete Challenge
                            801442e90063 

Thanks to Revolution readers Jimmy Backus, Luis Arroyo, Togorianii, Daniel, Ben Walker, matrix, Bradly Casebolt, Chris Barrett, Roy Solis, and Snow-Stalker!