Some people believe it was either Mangle or Toy Chica.

However, the real culprit is actually Balloon Boy.

"But Chubba, do you have any proof?"

Of course I do, you silly goober.

Let's take a look at Phantom BB's jumpscare.

Do you see how wide open his mouth is?

But, what does it mean?

Well, it's quite simple.

It's a reference to the original Balloon Boy committing the bite.

Sometimes my genius is almost frightening.