Nightmare legit states that he is William's wickedness then shipping him to Evan/Crying Child

Or when you realize the funtimes are based off the Afton family but only one possesses it. (Two if you believe Mike's remnant is mangled in Ennard/Molten Freddy after being scooped.  Or just the possibility of Elizabeth's soul being split into all the funtimes each having their own personality.