Ron Moore: Help? Why would I need help writing plots? I just throw a dart at the cast list, and...boom! They're a Cylon! Rinse, repeat, cash the f*cking check. Watch! Sh'boom! Sh'bong! Sh'bing! Cylon. Please help me! This is so hard!
This trope refers to creating a fictional subcategory that can be applied to any character and then applying it ad nauseam to most of the cast. Possibly as a method to create a Meta Origin (it usually fails).
Note: This is a Spoilered Rotten trope, that means that EVERY SINGLE EXAMPLE on this list is a spoiler by default and most of them will be unmarked. This is your last warning; only proceed if you really believe you can handle this list.
- Mahou Sensei Negima! is a bit guilty of this. Although most of the cast was considered normal at the start of the series (excluding Sayo the ghost and Chachamaru the robot,) since then it has been revealed that Yuuna, Misora, Konoka, Hakase, Takamichi, Chao, and the Headmaster were all involved in magic from the beginning, and Evangeline, Mana, Zazie, and Setsuna are demonic. Asuna is practically her own category.
- Neon Genesis Evangelion: You know those alien monsters humanity has been fighting throughout the series? Humanity is one of them.
- Lampshaded in the Great Lakes Avengers, where the team renamed themselves The Great Lakes X-Men after it was revealed that the entire team was made up of mutants.
- This was also a parody of the then popularity of various "X-Titles".
- It's a justified trope in the Marvelverse, mind; all the other origins are one-in-a-billion freak occurrences, or inventions by 99.999999th-percentile geniuses who for some reason keep their potentially world-changing inventions to themselves. Mutants are a demographic.
- By the finale of Strangers in Paradise, nearly every female character in the series except Francine turns out to be a current or former Parker Girl.
- In the Doctor Who (Titan) story "The Twist", all of the human inhabitants of the Twist are not descended from the original colonists, who all died in an accident, but humans genetically reconstructed by the sentient descendants of the foxes also carried on the starship.
- When My Little Pony: Friendship Is Magic revealed the existence of shapeshifting changelings, fanfics with the premise "X was secretly a changeling all along" started popping up—enough to become a cliche. Three different authors independently parodied the trend by writing stories where everyone was a changeling all along: Changelings, Changelings Everywhere, Changeling, and Everyone's a Changeling.
- About two thirds into Identity, it's revealed that every single character at the motel is a personality of Malcolm Rivers, and the whole movie was a plot to kill off his alternate identities, curing his Multiple Personality Disorder.
- In John Carpenter's The Ward, the ghost, and the women she's trying to kill, turn out to be a result of one character's multiple personality disorder.
- Chrestomanci: In Witch Week, the protagonist is secretly a person with innate magical talent in a world where such "witches" are feared and hunted. He learns that one of the other students at the school he attends is also secretly a witch. Then another. And another. Also, some of the teachers. (The deputy principal isn't really a miser, he just has no money because he's a witch and the principal is blackmailing him with the threat of exposure. The principal, unbeknownst to him, is also a witch.) In the end it turns out that, as a result of a supernatural event in the 17th century, everybody in the world is a witch, but they're all hiding it from each other for fear of persecution.
- The Discworld novel Monstrous Regiment is about a Sweet Polly Oliver going off to war. Gradually over the course of the story, she discovers that more and more of her comrades are also women, some in more convincing disguises than others. All of them, in fact, including the troll. Even the bluff old Sergeant Rock, who also happens to be aware that a good third of the high command are women in disguise, along with Nuggan-knows how many of the troops. The country has been at war for so long that all the men have simply been killed off.
- Older Than Radio: The Man Who Was Thursday (1908) by G.K. Chesterton: The hero, who is an undercover policeman is drawn into the murky world of anarchists. He discovers that one of their number is also an undercover policeman. As the story continues, his attempts to apprehend anarchists force all of them to reveal that they are policemen, too.
- The second Battlestar Galactica made nearly half the cast Cylons. Although there was plenty of evidence to suggest that Tyrol was one, and even that Tigh OR Ellen was one — which necessitates the other. Not to mention precedent of sleeper agents. This was not planned out in advance however, but rather a hasty improvisation by the writers.
- Buffy the Vampire Slayer: At the start of the show, only Buffy was anything other than a normal human, but by the end, several supernatural beings had joined their group, and almost everyone else had learned how to practice magic.
- Doctor Who: In "Full Circle", the inhabitants of the Starliner are not descendants of the original crew and passengers, but descendants of indigenous life-forms who massacred them and then took on their forms.
- Dollhouse: Lubov is a doll! Mellie is a doll! Saunders is a doll! Season 2 brings even more.
- The Good Place is about what happens when someone who was a petty, selfish jerk on Earth is sent to Heaven after they die due to a mix-up. Except that she actually is in Hell. And the other three humans there who think they're in Heaven are also in Hell. And everyone else is a demon. Except for the anthropomorphic computer program.
- In the Star Trek: Deep Space Nine episode "Shadowplay", Odo and Dax beam down to a village and investigate the disappearance of a number of villagers. It turns out the village and its inhabitants are holograms - news which they take surprisingly well - and the device that powers them is wearing down. Dax is able to fix the device, but not before discovering that the village elder is a flesh and blood life form and the creator of everyone and everything around him. He doesn't want his fellow villagers to know he's different from them and responsible for their existence; Dax and Odo agree not to tell them.
- True Blood: The folks with powers will soon outnumber the normal people in Bon Temps.
- V (2009): Seems like every third character is secretly a V sleeper. Two of Erica's FBI partners were Visitors—not to mention her obstetrician.
- Part of the point of Paranoia is that player characters are dystopian special forces charged with exterminating mutants and secret society conspirators. The players, but not their characters, are fully aware that everyone in this dystopia is a conspirator and mutant.
- From Kingdom Hearts II onwards, almost every single mysterious character manages to be a form of Sora, no matter how illogical or unlikely it seems. The only ones who aren't are the ones who actually turn out to be a form of Xehanort.
- Subtle one in Silent Hill 2, all male models in game who aren't Eddie are James. Pyramid Head, the corpses all over the place, the prisoners, the Lying Figures, all of them. Similarly, most female models are Mary.
- Right near the end of Assassin's Creed II, you find out that every helpful adult not your mother or named Leonardo DiVinci is an assassin that's been helping you become one of them.
- Xenoblade Chronicles X quickly follows up a surprise Robotic Reveal of the protagonist by revealing that all the "humans" in New LA are Ridiculously Human Robots, and that the protagonist, by virtue of having no memory, was literally the only one who didn't know this from the start.
- In It's Walky!, several cast members are revealed to be former abductees.
- Parodied in Futurama, with an episode of Calculons soap opera where characters keep announcing they have Laser-Guided Amnesia to the point that it starts to get annoying. Is there anybody here who doesnt have amnesia?!
- Neo Yokio: Near the end of Charles' story in "Pink Christmas", Kaz reads Aunt Angelique's memoir and discovers that his demon-hunting Magistocrat family actually has demonic ancestry. Later, the Great Demon confirms this and takes it a step further: not only is the Kaan family descended from demons, every single Magistocratic family is descended from a group of demons who used their powers to hunt other demons in exchange for money and social standing, making every demon hunter a demon in disguise.
- By the late 1950s, the Communist Party USA was in heavy decline thanks to McCarthyism. However, the FBI maintained a paranoid obsession with it, and dedicated huge resources to tracking it, to the extent that undercover FBI informants made up as much as 30% of the party, and were crucial to its continued finances. J. Edgar Hoover later admitted that ironically, the FBI's undercover membership bolstering and financing of the CPUSA probably enabled it to avoid collapse.