Hold X+Y+Z and press start on Controller 2 while the words "Press Start Button" are flashing (title screen). Now press start on Controller 1 to see that BATTLE GAME is now playable.
NOTE:You must have a saved game to play in the BATTLE GAME.
Choose "New Game" from the main menu, then select a character. When the words "1998, July" appear, press and hold L and R on Controller 2 until the game starts.Now your character will have different clothing.
Thanks to Revolution reader Dimon Hunter!