How do we know that the Mangle was the biter? At the end of night 6 in fnaf 2 the phone guy tells Jeremy that he'll be on birthday duty tomorrow. He also says that the animatronics have been acting strange and to stay near them. Why would the mangle be active during the day if it's all over the floor? Since Mike was the one who was closest to them, and since the animatronics seem to target security guards, it was probably one of the fully-functional animatronics.