I think I just solved FNaF Security Breach (and a lot in the other parts of the timeline.
Yes, the title is correct. I solved FNaF Security Breach.
I was thinking about how the withered animatronics apparantly represent how the children died (I know I know it isn't confirmed, but I'm pretty sure it's not denied), and it got me thinking.
What if William had a reason for killing them like this?
In FNaF, emotions seem to give more powers. Apart from his kneecaps being ripped off, the kid for withered Freddy got the least painful death. Withered Freddy is also the most animatronic like. Cassidy got killed last, saw the most and probably got the most trauma, and most emotion. Golden Freddy is also the most powerful, and its head can float.
Cassidy made an eternal hell for William and traps herself there with him, with her hatred. Again, emotions create powers.
Also, William might've come back several times out of fear of what Cassidy had become. Not from remnant, not from dying near an animatronic. FEAR.
So perhaps William got tortured in UCN for so long that he eventually got the willpower to escape, went into a computer, and eventually got his old body being burntrap back. Then Cassidy possesed Glamrock Freddy in order to protect and make sure William never kills again. Micheal most likely also sensed that William was back and possesed Glamrock Freddy too.
So maybe, just maybe. Steelwool was onto something...
And I don't think remnant is as important as people think. I think William used it in Sister Location because the children would die too painlessly, so the remnant would help.