Bonus Level
Beat the game in "TAG TEAM" Mode with the difficulty set to VERY EASY with only one character (don't let anyone join you) in under 21 minutes. You'll get a new stage next to the ring with a Tokyo Theme to it.
Alternate Outfits
Before selecting your player, hold the L button and press left or right on the digital pad. The rotating character pictures will change color indicating the trick worked. Keep holding L when you select your character.
Credit Goes to: IGN 64