Okay, so there's this mutant named Andy. He had this exceptionally helpful ability to basically expel any curse, spirit, or demon that was inhabiting someone and contain it within himself. His soul and mental state were both strong, so it didn't cause any problems for him except some migraines and the occasional chest pains.
Well, he finally met his match with a powerful archdemon that tortured him and eventually killed him. Now, if you know ghosts, you know this is a recipe for a vengeful spirit. But, this particular dark spirit... It was different. Every single demon, ghost, or curse he had contained inside of him was now connected to that soul and became one being. Essentially? Andy became a very powerful dark ghost lord or even possibly a dark god.

He has the knowledge and power of thousands of spirits, curses and demons. I don't need to elaborate on how much power he has within him.