Hold either B+A+Left+Down or LB+A+Down during the copyright, SCI Recordings or "Aaron Teplitsky Presents" screen. Do not let go until the Debug Menu appears. From this menu you will be able to unlock all hidden content instantly and/or disable user profiles. These settings do not save; if you want to use them, you must enable them each time you start the game. This code only works in version 1.1; if you have an older version you can download the update for free. Delete the game, then re-download it to get the update.
After each stage, in all modes, you'll see a short instant replay (lasts about 5 seconds). If you would like to repeat the current short replay, press X before the replay ends. If you would like to see a replay of the entire level, press Y before the replay ends...great for Battle modes!
On the Main Menu you'll find a Goal Board with 12 listed goals. Completing each goal will unlock a hidden feature.