TL;DR: Vampire outsmarted me and became a god.
So I was DMing the 5e version of the lost mines of phandelver which BTW, became a homebrew afterwards. So this is the tale of Edwin the Unkillable. (which is actually ironic because he had died at one point in the campaign but he was brought back) so they were level ten when I realized just how much I had messed up. I had given the evil vampire a beholder friend (story for another time) named Kyle. now Kyle wasn't a beholder, he was actually the greatest lich in an the realms taking on the form of a beholder. and he was a time traveler. and I had made the mistake of having Kyle set up a mini realm where they could test out homebrew magic items. Now Edwin is a genius, and he tested something which I still don't understand he somehow figured out something weird that you wouldn't understand even if I did explain it. So he effectively asked for pizza and it was a homebrew item that someone had made.
DM (me): He gives you a slice of pizza.
Edwin: I eat it.
That back and forth goes on for a while until a little bit later, when he was in a prison that I had made that was hidden away by Kyle.
Edwin: I would like to speak the most intelligent and ancient creature there. After A pretty gnarly description of his cell Edwin managed to persuade Kyle into letting him talk to him.
Edwin: is it possible to become one with the realms and make them into a phylactery? I thought about it for a little bit trying to figure out how he was going to do that.
Ancient Creature: It may however it may also lead to something far worse.
And so taking advantage of Kyle's traveling abilities he gathered every thing he needed and he ascended and truly became a god. So yeah now he is an immortal lich with an empire that has lasted hundreds of years.