So in MY cannon Yellow Bear is a seperate suit from Fredbear and Freddy, being a middle child of sorts that Gron used on his first victim, then not long after, William did the same using the same suit for a different kid

So its possessed by 2 spirits and can also shapeshift though nit hy much, which is why they have a different design in each game

They use the Nearest Freddy design to shape into even tho the suit will always have damage and sometimes a corpse (like the first game)

Now onto their mechanic

In the 2nd game they can not only appear in the office or the main corridor, but also every camera, as a hallucination and in all 3 hallways

To get rid of them you h-have t-t-t-----*****---........^^__<_(*^%!!×_<[[[[>_//::,((*^%$#÷_>[[[>><__//$