To gain Access to special costumes hold the L and R triggers on controller 2 at the ''July 1998'' screen. While holding them down, press START on controller 1.When the game starts you should have new costumes.
Hold X, Y, Z and Start on Joypad 2. Press start on controller 1. Note, you must have saved the game at least once for this to work.
Simply defeat the game once and the Battle Mode would be unlocked permanently. In other words Battle Mode would be available even without cheat.