These are cases where a strange or fantastic creature eventually turns out to actually be a member of Homo sapiens a human being or a human subspecies.
Since humans make up the majority of fictional characters, and being a human isn't (normally) regarded as a strange character attribute, this is often used as an inversion of traditional reveal tropes (such as Not Even Human).
Often, the humans initially appear inhuman because of a Baleful Polymorph, or because of being some form of transhuman. Compare Actually Not a Vampire (though not all instances of Actually Not a Vampire are human; they're just not vampires.) A subtrope of Was Once a Man, where an individual monsters turns out to be human.
WARNING!! Spoilers ahead!
- The Jovian lizards in Martian Successor Nadesico turned out to be humans.
- The UE from Mobile Suit Gundam AGE are actually members of Vagan, a human nation formed by colonists who were abandoned by the Earth Federal Forces 150 years before the start of the series.
- In Eureka Seven, Anemone's appearance and role (and possibly her name) seem to imply that she is a Coralian. It turns out she's just a human whose appearance and abilities have been modified by horrible military experiments.
- In Claymore, the youma turn out to be humans infested with parasites born from the flesh of the Descendants of Dragons.
- In Berserk, it turns out that the demons are all former humans who reached a Despair Event Horizon and made a Deal with the Devil. In the apocryphal "lost chapter" of the manga, it is revealed that the "devil" in question is a godlike being born of humanity's collective unconscious, so we can't even blame it on demonic interference.
- Yoruichi of Bleach, who appeared to be a Talking Animal but was actually a human (soul) disguised as such.
- In One Piece, It's turn out that the living toys in the Dressrosa Kingdom actually were a human before the Donquixote Family transform them.
- This becomes a crucial plot point in Gargantia on the Verdurous Planet. Ledo, a soldier of the Galactic Alliance, fights against their hated enemy, an alien force known as the Hideauze bent on destroying humanity in space. He later learns after being stranded on Earth that the Hideauze, which were also present on the planet, were genetically modified humans originally known as the Evolvers. He doesn't take this news well, especially as he had just slaughtered hundreds, if not thousands of them hours before watching the old recordings and news reels detailing the origins of the Hideauze/Alliance war on Earth.
- Witches from Puella Magi Madoka Magica are terrible-looking surreal beings who rouse death and destruction... and they are the final form of Magical Girls. Oh shi...
- This is the basis of Interviews with Monster Girls, when monsters of the folklore were found to be just mutant humans some time before Present Day.
- Takeshi Hirokawa from Parasyte, actually turns out to be a normal human that was leading the parasite colony in East Fukuyama City, using his power as mayor to help them to kill and feed undetected. He was an extreme misanthrope who believed that humans needed a predator to cut them down for the harm they'd done to the environment.
- The titular Titans from Attack on Titan. All were members of the Eldian race, a group of humans that possess an unique trait allowing them to be transformed into a Titan. What makes this discovery even more horrifying are the revelations that the characters are themselves Eldians and that all the Titans they've been fighting are poor souls that were transformed as punishment by an oppressive enemy nation.
- Anthropology: Lyra. Princess Celestia turned her into a pony to hide her true identity, which explains her obsession with humans.
- Left Beyond: True of both Dwarves and Angels - both come about as a mutation upon the human genome, aided by Narrative Causality (accidentally in the first case, by Yahweh's hand in the second). By the time of the Last Battle, and in the Tripocalypse continuity, allografts are common and available enough that the furry subculture has quietly died down due to having become nothing special.
- Five Score, Divided by Four: Inverted example, they were ponies the entire time
- In the Pony POV Series, it's revealed the Changelings aren't a separate species, but a lost tribe of ponies descended from the Flutterponies. Even the Changelings themselves were unaware of this.
- One of the twists in Pandorum is that the creepy alien mutant cannibals are descended from humans who've evolved to survive in a foodless spaceship over a thousand years. It helped that their ancestors were dosed with a treatment that caused accelerated evolution.
- In the film version of The 13th Warrior, the protagonist gain some courage in battle when he discovers that the Vikings' monstrous foes the Wendol are just men dressed up in bearskins. Later in the film, he and the rest of the band stumble upon a cave filled with the skulls of the Wendols' many victims. He says he was wrong earlier, and claims that the Wendols are not men.
- The Big Bad of Star Trek Beyond turns out not to be an alien, but a human officer from Earth's pre-Federation military who found alien Lost Technology that mutated him, extended his lifespan, and gave him control of an army of automatons.
- In Dragonback, the long-lost original hosts of the K'da were called the Dhghem. Turns out that's actually "Human" in a really old language.
- The koloss and kandra from Mistborn both turned out to be transformed humans.
- In The Hobbit, Gollum is described as a strange and nasty creature of undefined origins. In The Lord of the Rings, we get to know he's in fact a hobbit whose appearance and personality were twisted by centuries of exposure to the One Ring.
- The monster from The Relic is actually the missing scientist from the prologue, mutated beyond all recognition.
- In Pact, Rose Thorburn is introduced as a vestige of Blake Thorburn, her Distaff Counterpart, a version of himself who was created artificially, lives, in mirrors, and is doomed by her nature to slow decay. It's later revealed that It's Blake, not Rose, that's the vestige-he's a bogeyman loaded with Fake Memories to make him think that he's human, and Rose is the real human of the pair. And then it turns out that neither is more 'real' than the other. Blake and Rose are the soul fragments of the real Thorburn heir who was split apart by The Barber.
- In "Merlin's Gun" (a Alastair Reynolds short story), the Absolute Xenophobe fleets that swarmed out from Dyson Spheres near the galactic core millenia ago and have since then been eradicating every human ship and colony they come across are revealed to be human, albeit heavily modified with cybernetics.
- In Girl: Who are you? Alien: Er, Im an alien., this is inverted with the girl, who's technically the real alien by our standards. However, this is played straight with the alien, who's actually a human in a distant future where humanity has developed drastically, and can now explore space.
- Happens occasionally in the Land of Oz series:
- In Rinkitink In Oz, King Rinkitink's talking goat steed is revealed to have been a Baleful Polymorph that was previously a prince.
- In Kabumpo In Oz, the living doll Peg Amy is revealed to have been the lost princess of Sun Top Mountain, and the princess that the protagonist was supposed to marry to release his kingdom from a spell.
- Doctor Who: The series 3 finale ("Utopia"/"The Sound of Drums"/"Last of the Time Lords") has two examples:
- The Toclafane who appear in the latter two episodes were the last surviving humans from the first episode, who turned themselves into Psychopathic Manchild Cyborgs to escape the universe's final collapse.
- The Face of Boe is actually a human after eons of Age Without Youth, specifically Captain Jack Harkness.
- In an episode of Star Trek: The Next Generation, transporter-phobic character Barclay, when forced to travel via the transporter, sees some strange virus-like creatures in the matter stream. After suffering greatly due to his fears, he eventually figures out that those strange beings are actually humans, stuck in the pattern buffer.
- There's one episode of the original Twilight Zone, titled "The Invaders", where a woman is getting unpleasant visits from tiny alien invaders. But those people turn out to actually be human beings from Earth: the woman's world is the alien planet and the woman we've encountered is a humanoid alien giant.
- An episode of the 1980s Twilight Zone had this as well: In one episode titled "Hunted", a group of soldiers were hunting down a monster known as the Kreetor. Turns out that the Kreetor is a human being, and the people we thought were humans are actually robots. We also initially assume that "Kreetor" is a linguistic devolution of "Creature". Turns out it was actually from the word "Creator".
- In the end of Phantasy Star II, the creators of Mother Brain are revealed to be an alien race who were planning to conquer the planets of the Algol system. Their homeworld? Earth.
- A subdued version appears in Metal Gear Rising: Revengeance: all of the enemies Raiden fights throughout the game are cyborgs who, like himself, are practically entirely mechanical except for their brain. When he finally defeats Jetstream Sam, however, he discovers that his rival had virtually no cybernetic enhancements whatsoever. This is particularly prominent in the Japanese version of the game, where cyborgs bleed white artificial blood, but Sam bled red.
- This is the big twist behind the Shades in NieR, though the backstory for it is rather complicated. The events of Drakengard's weirdest ending introduced a magical plague to Earth that forced humans to separate their souls from their bodies and store them until an army of Artificial Humans cleaned up the planet. Unfortunately these Replicants developed sentience, forgot their origins after completing their mission, and built their own civilization in the world's ruins. By the time of the game the Replicants are slowly dying out due to complications like the Black Scrawl disease, while the humans' Shades have started going insane without their bodies, with many devolving into ravening shadow monsters. There was a plan to put things right and reunite the Shades with their Replicants, but by the end of the game, Nier kind of killed it.
- Futurama: Leela claims to be an alien cyclops woman who has been trying for years to find her home planet. But she's wrong. She is actually a mutant born from mutated human sewer dwellers on Earth, who gave her up and attached an adoption letter written in alien language as a way to give her a better life.
- With the occasional exception, pretty much every last Scooby-Doo villain is actually a human criminal pretending to be a monster or supernatural creature. And they would've gotten away with it too, if it wasn't for you meddling kids.
- The protagonists of Code Lyoko, including Aelita herself, spent the first two seasons thinking that she was an AI, but the end of the second season reveals that she's not only human, but the daughter of Franz Hopper, the creator of Lyoko.
- Dr. Victor Falco of Teenage Mutant Ninja Turtles (2012) says that his partner, with whom he was experimenting with mutagen and psychic powers on a chimpanzee, was captured by the Kraang. But he's lying: Falco actually forcibly experimented on his partner and mutated his partner into said chimpanzee. The poor guy took a couple of seasons to get his intelligence back, and still looks like a chimp.
- In the pilot episode of Bonkers, Lucky gets into a scuffle with the defeated Toon villain The Collector and pulls off one of his gloves, revealing that he has five fingers. Since Toons in this series all have Four-Fingered Hands, this clues in everyone — including The Collector's own unaware Toon henchmen — that he is not a Toon. Lucky pulls off his mask, revealing that the Collector is indeed human. Disturbingly enough, the Collector keeps insisting he's a Toon afterward.