Idea for Killer backstory
I had an idea for a Killer to have started as a Survivor long ago (or in the future).
This would be a Survivor who won trials all the time. Looped the Killer for the five gens and would get saves off hooks. This would happen all the time and the Survivor got tired of the trials being too easy and boring. In one of the chases the Survivor tried to go easy/change things up on the Killer and accidently sandbags a fellow Survivor. They get a rush out of putting others in danger and changes up the "game". Every trial they go into afterwards they loop the Killer for at least one gen, get the other three Survivors killed and escape through the hatch. This goes on trial after trial making surviving exciting again. Until one day, they go into a new trial and they're up against four Survivors.
Long story short: Toxic Survivor turned Killer!
If the Survivor is female: I was thinking a pretty innocent looking girl, someone you'd never suspect of wanting to hurt anyone and when they turn Killer their design can be like a doll. A transparent body where you can see the Entity's tentacles and black fog and their face can be made of porcelain.
If the Survivor is male: I'm thinking an amputee (unsure if the amputations should be war related or medical condition) and when they turn Killer the Entity can give them freaky grotesque limbs.