(A little unfair to start off the FnafTale series with the final boss, but I digress)
You heard about this in the extremely popular Vincent artwork. It's a set of stories, it's Undertale with FNAF characters. Here's the main characters.
Frisk: Mike Schmidt
Sans: Golden Freddy
Papyrus: The Puppet
Toriel: Chica
Undyne: Mangle
Alphys: Foxy
Mettaton: Bonnie
Asgore: Freddy
Flowey: Plushtrap