#dr talbert

The climax revolves around two characters (Everette Larson & Jake (the Stitchwraith)/Lankester Merrin & Damien Karras) entering the house of a parent (Dr. Talbert/Chris MacNeil) and having to defeat the demonic presence within their daughter ('Renelle Talbert' inhabited by the shadow, albeit it's an entity pretending to be Renelle/Regan MacNeil inhabited by Pazuzu)

The possessed daughter is laying down on something ('Renelle' on a table/Regan on her bed) and a strange fluid is coming out of her body as sort of an attack against the other characters (dark Remnant coming out of 'Renelle'/green slime coming out of Regan)

After one of the protagonists is incapacitated (Larson passes out/Merrin has a heart attack), the other protagonist has to defeat the demonic presence by allowing it to enter their body (Jake absorbs the shadow into himself in order to seal it inside a memory/Karras allows Pazuzu to leave Regan and enter his body before jumping to his death)

Some time later after the parent has reconciled with their daughter (Jake reunites Talbert with the real Renelle/Chris and Regan reunite), the parent gives one of the characters a silver medallion that was relevant to the climax and he's left to ponder it on the sidewalk (Talbert gives Renelle's heart pendant to Larson/Chris gives Karras' Saint Joseph medallion to Joseph Dyer (although in the Director's Cut which I watched Dyer gives it back))

Ever since The Silver Eyes (which was being written since FNaF 3 came out) it's been well-established that emotional bonds are what tie spirits to objects, and Fazbear Frights repeatedly shows this.

I'm convinced that agony has a greater energetic radius and power than any other emotion. I have done numerous experiments to measure, capture, contain, and study the leftover emotion embedded into objects that were near a tragedy. My work is focused on the hypothesis that you can take a saturation of energy, add any kind of intelligence--even an artificial one--and they will combine together to transmute the energy of emotion into the energy of physical action. This, I believe, is what explains what people call 'haunted' objects. -Dr. Phineas Taggart

Possession requires an emotional attachment. William was emotionally attached to the Spring Bonnie suit he got trapped in. The June 26th victims had emotional attachments to the Fazbear characters whose animatronics they were stuffed into. But a random Freddy's employee dying in a spring-lock suit doesn't result in possession because those employees don't care.

There's two main contenders for who would possess the plushie: Cassidy and Charlie. And neither of them have any emotional attachment to the plushie.

Possession is also implied to require something else: metal.

In nonscientific terms, [remnant is] like the metal is haunted. It’s more complicated than that, of course, but it’s similar to the way that water conducts electricity. Remnant is the mixing of the tangible with the intangible, of memory with the present. The people and things that are lost—it makes them almost real again. -Dr. Veinerfarten Talbert

Although the plushies are implied to have cameras in them, I wouldn't say there's a significant amount of metal to possess, and I certainly don't think it was canon as of FNaF 4's release, and therefore would be impossible to deduce.

There's really no way for Cassidy or Charlie's remnant to be transferred from their respective animatronics to the Fredbear plush, either. If this is a case of possession, this is a case of a spirit inhabiting one object deciding "Hey, I'd like to inhabit this other object for a second to talk to this child, and then I'll go back to my original object," unless there's some physical transfer of metal between the Fredbear plush and Fredbear animatronic or Puppet.

The spirit follows the flesh, it would seem, and also the pain. -William Afton

So, in conclusion, the FNaF 4 plushie isn't possessed.

What is possible is that (a) Cassidy is taking the form of a plushie, specifically one that does have a physical counterpart, as she is able to take Withered form in FNaF 2, or (b) that the Bite Victim's agony poured into the object and he was able to speak with it, which, at the time of FNaF 4's lore, would've been as simple as it being the child's imagination and trauma.