Drakengard 2 - PS2

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.