- Ass Pull: For some, Charlie's Robotic Reveal came off as this. Many believed it came with little to no Foreshadowing and the fact that she could do literally everything a human being could do, including eating and sleeping, felt completely unrealistic and confusing.
- Complete Monster: The killer returns yet again. See that page for details.
- It Was His Sled:
- Just like in Sister Location, Elizabeth Afton was Baby's first victim and was ultimately possessed by her.
- Charlie was the real first victim of William Afton, not Sammy. The Charlie seen in all three novels is really an animatronic, given something resembling a soul by Henry's love for his daughter and grief over her death.
- Jerkass Woobie: Elizabeth/Baby. Elizabeth was neglected and abused by her father and then killed by Baby. Baby was initially created to be Charlie's adult body but received none of Henry's love and was later taken and modified by William. The combination of the pair is a bitter, homicidal animatronic still looking for love and approval.
- Moral Event Horizon: As tragic as her past may be, there is nothing forgivable about how Elizabeth Afton/Baby killed Aunt Jen while impersonating Charlie by choking her and ripping out her stomach never letting the real Charlie make amends with Jen.
- William Afton crossed it many, many times, but this book shows him at his worst. In the present that the book was set in, he was willing to continue his evil legacy by using his killer robots to abduct children. When Carlton finds himself in the afterlife of the victims of the Missing Children Incident, it's shown that William dressed up as Spring Bonnie and got the kids to trust him before killing them, especially brutal for Susie when he lied to her about finding her puppy before giving her the same treatment. The Wham Line at the end shows that William killed Charlie when she was only three. However, he undeniably crossed the line when it's shown that he was a horrible father to Elizabeth even before he started his murders, stomping on her paper and hitting her when she was only trying to make him proud of her, which prompted her transformation into Circus Baby in the first place in a desperate attempt to get him to notice her.
- They Wasted a Perfectly Good Character: Sammy. Much of Charlie's trauma revolved around losing him and in the Twisted Ones she claimed to feel his presence. Despite the confirmation that William killed Charlie and Sammy is likely still alive, Sammy doesn't appear on-page.
- The Woobie: By the end of the book, you have to feel sorry for John. First he was suspicious of his miraculously alive again best friend to the point it seriously affects his life, then he discovers he was right and discovers the real Charlie - finally allowing him to believe that she ''did'' survive. But then by the end of the book, she's gone once again and what's worse, "Charlie" never really existed as he knew her. The real "Charlie" had died years and years ago, and he had only ever known a very human robot...
YMMV / Five Nights at Freddy's: The Fourth Closet