User blog comment:TonicHedgefox/An announcement./@comment-6490352-20150725170934/@comment-25535739-20150725215001

If Withered Freddy caused the bite, the company would have gotten rid of the Withered animatronics permanently. And we can clearly see Freddy and co in FNaF 1, without their toy counterparts. This means one of the Toy animatronics must have caused the bite.

We can rule out BB and Puppet, since their mouths don't work.

Toy Chica can also be ruled out due to the fact that her beak comes off extremely easily.

Toy Freddy is plausible, due to his jaw being able to open fully, Toy Bonnie's teeth could perhaps have caused the loss of a frontal lobe, however, they don't look too sharp.

And, if you're just going off jumpscares, Freddy is more up in the player's face while Mangle...