WARNING, THERE WILL BE SPOLIERS. FNaF3 Spoilers, to be exact. Do not read if you don't want to be spoiled.
I'm talking to you, Frederson.
...that's not even a name fff-
This theory involves the three rare images that can appear at the beginning of the game. What can be seen looks much like the Springtrap ripping it's own head off, much like the poster in FNaF1. If you look inside, you can see what appears to be another face inside of it, with tiny human-like teeth. What if I told you that wasn't an endoskeleton head?...well I mean, that should be obvious, it looks nothing like it.
First off, let's look at the final death minigame. You play as the dead child from FNaF2, as you roam around the new(FNaF1) building, except it appears to be deserted, with a dripping ceiling and mice everywhere. Usually, you play as one of the four animatronics while a purple Freddy Fazbear instructs you to follow him, ultimately leading you to a room in which you can't escape your unfortunate demise from the Purple Guy destroying you. In this particular minigame, however, there is no Purple Freddy, and you can actually walk into the room you couldn't previously before. Inside the room are four other dead children and the Purple Guy, panicking as you chase him around the room. He eventually jumps into the Springtrap costume, and stares at you before the springlock fails on the suit, and he ultimately bleeds out. Think about that for a second. You can see the Purple Guy inside the Springtrap slowly lowering, until he's sitting against the wall as he dies. Now, this room itself is empty in itself, except for a few arcade machines. If you look at the trailer, it shows footage of the camera zooming in on a Springtrap, sitting down against a wall in an empty room. So, what does this mean? It means that this minigame took place in the past, seeing as the building is still deserted before the new people arrive and makes Fazbears Fright, in which the Springtrap is the only working animatronic. Back to what I talking about at the beginning, that face inside the Springtrap...is the Purple Guys skeleton. Woah, now. The games never had THIS much violence. I mean sure, the eyes and teeth popping out the suit, pixelated blood in the minigame, yeah, but nothing this extreme. But think about it. As the Phone Guy said, it is possible for a person to get inside the suit, as long as the Springlock doesn't fail and kill the employee inside. Seeing as that's what the Purple Guy did, he basically IS the Springtrap, and that is his skull. His skin and face muscle decayed from a long long while inside the suit, 30 years will do that to you. (Some people have actually said that they see human insides in the suit, too, but all I see are eires tbh.) So, that's my theory, I just hope it isn't too gore-y for any of you out there, and I'm sorry if this is a little long, I worked a lot of time on this, and I hope you think it makes sense.
The W0t Returns.