Like any good villain, William gets his comeuppance from the instruments of death he constructed to carry out his murders. Sneaking into the pizzeria to collect the supernatural residue from his victims left in the animatronics, William is ambushed by their ghosts haunting the robotic suits. William is stuffed into a spare Spring Bonnie animatronic and crushed to death in the same manner as the killings he carried out. However, just like those he murdered, William finds his spirit haunting the animatronic he is killed in, taking on the nickname Springtrap.
Just as deadly post-mortem, William’s spirit goes on to haunt other animatronics in later games after Springtrap is eventually destroyed. The franchise needs an antagonist that’s human, not just a largely silent animatronic, and William fulfills that while adding to the lore. William’s eventual death at the hands of his murderous creations feels both cathartic and poetic, and fitting of his crimes. And if there’s anything that could set up a potential sequel, William’s monstrous rebirth as Springtrap lends itself perfectly to that possibility.