Dark Lord

Achieved by slaying the Demon King and ruling over Hell.

You can get this ending by:
 * 1) Activate all 5 monoliths
 * 2) Enter Hell through the stone arch
 * 3) Blow out the 3 blue torches in Hell
 * 4) Head to the Demon King's throne and slay him
 * 5) Choose to stay in Hell and rule over it