So, one of my players is playing a Fleshwarp and he left his backstory up to me to generate plot hooks with. We're playing Extinction Curse and I've had fun with that (no EC spoilers in here, don't worry!)
I wrote up a stack of post-it notes and have him draw from them every week or so of downtime. If he encounters things that trigger specific memories, he gets specific cards, but otherwise they're random, and they conflict with each other, heavily.
He's figuring it out in-character - though the player has already caught on - that there's more than one mind in his head now. It's not a possession, it's a gestalt that has found purpose in its unity. There is no 'him' to be possessed - he is a consciousness that arose from the combination, and if you separated them all, you could not find a single one of them that could identify itself as him.
This Dedication is an attempt to make something fun that allows him to double down on this if he wants to. Please let me know how you think this would be for a high-intelligence Fighter. It's my first serious attempt at formatting things on Scribe as well, so please critique that too.