After obtaining a specific Artifact in the game and meeting certain conditions, two extra difficulty levels can be unlocked.
To unlock Terror difficulty, you must find the Terror Medallion from of the Black Star armors found hidden in Chapter 4, Area 017. After getting the Artifact, clear the game on Hard mode and slay a total of 10,000 or more enemies in the game to unlock Terror Mode (your progress of how many enemies you slain can be seen in the Results screen and the Title Screen becomes increasing more red with each enemy killed). There is a chance you may not get the item from the Black Star armors, so bringing the Thief's Dagger may help increase the odds of earning it.
To unlock Nightmare difficulty, you kill the Nightmare of Legend in Chapter 3, Area 040. Once it's defeated and you've earn the Nightmare Medallion, clear the game on Terror difficulty to unlock Nightmare Mode.
|Unlockable:||How to unlock:|
|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.|