Needs More Examples. Needs a Better Description. So you meet someone who seems to be quite nice, friendly, very amiable, but something about them seems a little...off. Sometimes you figure that something's there behind their cheerful face, other times you've no clue anything's wrong because they're acting as normal as you'd expect them to be...but the truth is, they are not well. And once you find out, it's far too late to do anything about it. A frequent characteristic of the Serial Killer, and it may also be the secret that a Stepford Smiler is hiding behind his/her fake smile. It may come out if the character's Berserk Button is triggered, or through some other means via The Reveal. The revelation may happen in an instant, or little clues may be given here and there via gradual Sanity Slippage. If a nice or quiet person is secretly unwell mentally, and it eventually comes out, be afraid. And the scary part of it is, it could be anybody. Including your relative, your next-door neighbor, or your office-mate. Generally forms part of The Reveal in many a slasher flick or a psychological thriller. Note that while the Mask of Sanity is where a person disguises the fact that they're mentally sick, this trope deals with the moment of revelation when that insanity is unveiled, both for the audience and in-universe, thereby changing a whole lot of perceptions regarding the character and their points of. Contrast Obfuscating Insanity, where a character deliberately fakes madness. Also see Mind Screw, which messes with the audience's perceptions of what's going on, and The Ending Changes Everything, where an initially perceived view of a situation is altered at the end of the story by one detail being changed or revealed. As a Reveal trope, expect spoilers.
Examples include:Anime and Manga
- This may be the case with Tsutomu Tanaka in Kenichi: The Mightiest Disciple, as hinted in Chapter 521. When he first appears in the series during the D of D tournament arc, he is shown to have a habit of talking on the phone with his wife, and during his second appearance after that arc, he's revealed to be harboring intense hatred against Ogata Isshinsai for the death of his master/father-in-law. But in the most recent arc, while he's fighting Ogata after the latter interrupts yet another phone conversation with his wife by kicking the phone out of his hand, Kenichi gets hold of the phone and urges the wife to stay away from the park where the fighting is taking place only to discover that it's only a generic phone service voice recording on the other end, right at the same time when the Ryozanpaku masters are discussing the character's background history, with the implication being that Kensei killed Tanaka's wife and unborn child in the backstory as well, and that Tanaka went insane from that as a result.
- Misery does this with Annie Wilkes, who at first appears to be a helpful nurse assisting the main character, but who reveals herself to be psychotic when she finds out how he, the author of the titular novel series, plans to end his latest novel. This is more evident in the movie adaptation, whereas in the original novel Annie is shown to be nutty right off the bat.
- The murderer of And Then There Were None, Judge Wargrave, is a very collected and logical man in public but reveals himself to his last victim to be a ranting madman instead.
- When Charles finds out how Leo has been treating his pack in Alpha and Omega he assumes that Leo has gone "age-crazy," where a werewolf who is Really 700 Years Old goes insane as the world changes so much that it has become unrecognizable from the one they were born into. It turns out Leo has not gone age-crazy after all but his mate Isabelle did. Leo was just covering up for her.
- On one episode of Buffy the Vampire Slayer the titular character hallucinates being in a mental hospital. According to the doctors there, her memories of being the Slayer and all of her supernatural adventures are the hallucinations. At the end of the episode it is up for interpretation whether she was really insane all along.
- In Alan Wake, most everyone turns out to be at least partially insane. It is questionable as to whether the titular protagonist is partially hallucinating some of what goes on.
- In Dangan Ronpa, Junko Enoshima at first appears to be just another victim, but it turns out she faked her death via a Twin Switch and is not only the true mastermind, but an unstable multiple personality who gets off on people's despair - including her own. The sequel features Nagito Komaeda, who appears perfectly sane and helpful at first, but during the first school trial, it comes out that he believes that the best and only way he can help the "Super High School-Level" students he so envies is to kick off Monobear's murder game himself.
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