NOTE: This may NOT be the best theory, but it's my first.

So, you may remember the Jolly franchise, right? Well, here's a theory that I came up with. Jolly Entertainment owns the "Jolly" brand and is rivaled by Fazbear Entertainment and CTC Entertainment. But what if there is a 3rd rival to Jolly Entertainment. What if the 3rd rival company contains an Animatronic that secretly kills other animatronics, including the "Jolly" robots? It could be a Yandere Animatronic or an Animatronic with an Identity Disorder.