So guys, what im thinking is that his ability might have come with some kindd of OP passive that goes all the way in making his life like a game. As in it forces all nearby monsters and dungeons to behave similsarly to the game.
@Eridian If I remember correctly I don't think he actually let the two girls get killed for his revenge, I'm pretty sure it stated that he used dark magic to view the dead body's memories, they were already dead when he got there.