Unlock Bonuses
Music Room - Find the Music Room Key in Chapter 6, in the area lower-right corner of the area before the corridor containing power-ups and ghosts.
Boss-Only Mode - Obtain the Mysterious Button from D'Artagnan in Chapter 5. Once obtained, press the Pause button at the Title Screen to play Boss-Only Mode.
Nightmare Mode - Obtain the Nightmare Medallion from the Nightmare of Legend in 3-040. Afterwards, clear the game on Terror mode.
Terror Mode - Obtain the Terror Medallion from the Black Star armors hidden in 4-017. Afterwards, clear Hard mode and slay a total of 10,000 enemies or more.