Mr. Endoskeleton
This is something I have decided to start doing. Random theories about games I have played, specifically Five Nights at Freddy's.
Mr.Endoskeleton
At first glance most people say that this is Golden Freddy's (Fredbear) missing endoskeleton that the murderer of the five children discarded so that he could use the Golden Freddy suit. This however, is not possible. In the second game, when looking at the feet of GF, you can clearly see that his feet still have their portion of the endoskeleton in them, so if Mr. Endoskeleton was GF's endoskeleton, he would not be able to stand because the feet would be missing on him. Also, people say that he comes out of the Marionette box, but have no proof of such. If he was actually coming from the box, wouldn't we at least get to see him popping his head out at some point? A better explanation to the Mr. Endoskeleton's mystery appearance is found by looking at the Marionette box when it is fully closed. A close look can reveal a shadowy ear shape that appears larger than Mr. Endo's ear, likely because of the closeness to the light of the actual ear. This means that he doesn't come out of the box. He sits near or next to it. But why exactly does he only appear when the Marionette is gone. I have come to a very odd conclusion. The Marionette tells it to. You see, assuming that the Marionette is possessed by the original murdered kid's soul, (more on that later) than if it follows common ghost lore, than it can be fueled by electrical energy that it drains from electronic devices, which allows it to do more supernatural things, which means that it uses poor Mr. Endoskeleton as a battery/meal. It also means that he crawls in the vents so the Marionette can feed on its power before/during/after killing you. But I digress.
If Mr. Endoskeleton is anything, he almost certainly is an extra Freddy endoskeleton that they no longer use. It would explain his lack of a suit, bear-like construction, and attempts at crawling in your vents like the rest of the animatronics. He simply doesn't know that he is no longer in use.