Basically, I'll take your OC's intelligence, problem solving skills, and anything that would be helpful to them into account to determine if they could survive Five Nights at Freddy's as a (mostly) normal person. I'll be mostly going over the original game, but will also skim through: FNAF 2, FNAF Sister Location, FNAF 6, and if they get through all/most of those, I may use Ultimate Custom Night as a sort of "final challenge" for them.
...and maybe Cassidy's bossfight from Frickbear's 3 because I really like that game.