Infinite Ammo:
     Up, Up, Down, Down, Left, Right, Left, Right, R Trigger

Unlock Battle mode:
     To  unlock  the Extra Battle mode, you must beat the game on both
Arrange and Original modes. Also once you do this, a short cinema will
show  with  a  zombie  of Brad. If you do not collect any items in the
very  beginning,  when  you  go down the stairs in front of the Police
Station,  Brad's  zombie  is there. Kill him and he drops a key to the
lockers in the Darkroom.