Hard difficulty:
Beat the game and save. Load your cleared file to start a new game under hard difficulty.
Extreme difficulty:
Beat the game under hard mode and save. Load that cleared file to start extreme difficulty.
Hidden endings:
Beat hard and extreme modes for 2 different endings.
Bonus Battle Selector:
Beat extreme difficulty, then collect all weapons.
Movie Viewer option:
Beat the game to unlock the movie viewer.
Thanks to Revolution Reader Drago and Snoeker!
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