God Mode
Begin a new game with the name B4K42. Hit pause during the game to find the selection for God Mode. Here, you can turn it on and off.
Unlock Every Stage
To unlock all of the stages in Campaign Mode, begin a new game with the name !EVAH! (including the exlamation points and capital letters).
Unlock Everything In Gallery
Start a new game with the name 105770Y2. This should unlock everything in the gallery.