the bite of 87 is believed to have been caused by mangle due to her being the most vengeful for her parts while the others don't have as much damage as mangle mangle was torn apart by children maybe making mangle vengeful for her parts back and due to a child soul might have been put into her this might be why mangle is attacking you in fnaf 2 because you might be the victim to do the bite of 87 on and that's my theory!