No one takes the saying "you are what you eat" literally; it's not as though being a vegetarian will make you a Plant Person, or eating pure beef will make you a Minotaur. Some non-human critters didn't get the memo though, because for them eating people means being people. For some supernatural, alien, or stranger creatures to pretend to be human at all requires that they make a periodic consumption of Human Resources. Or simply put: Ghoulie has to eat people to look like one.
For the non-human, this will allow them to shapeshift into a human form, potentially that of the eaten, though it may only allow them to become a human version of themselves. The non-human may use non-cannibalistic methods as well, for example a fae creature might steal the shadow of a human to maintain their Glamour, a mutant might graft skin or new appendages from healthy humans to avoid Power Degeneration, a robot or alien may use Replicant Snatching, and a vampire may have to drink blood to avoid turning into a hideous monster. It's worth noting that perfectly normal humans may be able to do this through a spell, ritual, or if they have the Cannibalism Superpower.
Depending on what the non-human takes, the victim may be mildly inconvenienced, severely injured or even killed. Some may be able to make a complete recovery, others will be scarred or crippled for life, and some unlucky souls will end up an Empty Shell, Killed Off for Real, or even Deader than Dead. Needless to say, this makes being nice pretty difficult.
Most non-humans do this in order to maintain a Masquerade, and pose as human. Especially Tragic Monsters may be doing this because they want to Become a Real Boy. Especially monstrous ones will enjoy Showing Off the New Body. If the non-human doesn't eat people, whether out of niceness or inaccessibility, they will revert to their Shape Shifter Default Form. Things may turn From Bad to Worse from there though if that entails turning into an unthinking, horrific monstrosity that can never fit in among humans. And of course things will Go Horribly Wrong if their cannibalism is also caused by a Horror Hunger, and deprivation has the nasty side effects of making them dangerously hungry. Subtrope of Eating the Enemy, Cannibalism Superpower, Collector of Forms, Face Stealer.
- Youma in Claymore can take the appearance of those they eat, and this also gives them the ability to draw from their victims' memories to fool their families (and eventually eat them too). Later revealed to be a lie. The Youma are really parasites that infest their victims' brains, mutating them into monsters and driving them insane with a hunger that only human entrails can satisfy.
- Buu of Dragon Ball Z can absorb his enemies whole, which grants him their powers, intelligence, and appearance (though usually just clothing). The heroes assumed he grew stronger with each absorption and so freed their comrades from Buu to revert him to a less powerful state. Unfortunately, they went too far and freed Fat Buu (who Evil Buu had absorbed), causing him to revert to his original state, which was even more psychotic than the others.
- Tamaki Amajiki, one of the Big Three of UA in My Hero Academia, has the Quirk "Manifest". He can shapeshift his body into things based on what he's eaten in the last twenty-four hours. In the debut of his power, he turned his fingers into tentacles from some takoyaki, his left hand into a clamshell from some clams, and grew bird wings and talons from some fried chicken. The Yakuza Raid arc reveals this applies to anything he consumes, as he manages to eat a crystal created from the Quirk of one of the Yakuza members he was fighting, allowing him to augument his appendages with crystals and win the fight.
- In Ponyo on the Cliff by the Sea, also by Hayao Miyazaki, Ponyo starts out as a goldfish-like creature but is able to become human after tasting human blood.
- In One Piece, Wapol "of Tin" ate the Munch-Munch Fruit, which made him an Extreme Omnivore. With his "Munch-Munch Mutation" power, Wapol can transform himself into objects based on what he's recently eaten, such as cannons, a house, and other miscellaneous snacks to turn himself into a massive tank.
- Rebuild World: Non-sapient example. Organic Technology-based monsters left behind by the Neglectful Precursors called the Old World, originally designed to serve as security for facilities, evolve and change their capabilities based on what monsters they eat, creating wildly different subspecies based on the assimilated capabilities. They do this via Nanomachines that also infect their brains allowing them to be controlled (however due to an obvious lack of maintenance from their creators, this programming is usually corrupted.)
- No-Face from Spirited Away gains the personality and physical features of those he swallows (gaining frogs legs, for instance, when eating a frog-man). It's possibly one of the reasons he wants to eat kindly protagonist Chihiro.
- Everyman from 52 actually only needs to eat a tiny bit of whoever he wants to turn into. But it turns out he really likes the taste of human flesh.
- Excalibur (Marvel Comics): The Warwolves leave their victims' skins and wear them, in a manner similar to the Bug in Men in Black. "We wear who we kill!"
- In Love and Rockets, the monster BEM disguises itself by killing action hero detective Castle Radium and stealing his body. However, due to the brain damage it suffered while breaking out of prison, BEM gradually begins to believe it is Radium, and becomes obsessed with tracking down and capturing itself.
- In Lucifer, predatory Jin En Mok demons Cestis and Saul take on the forms of humans they have eaten. It turns to horror for Cestis when she find herself trapped in the body of Elaine's father with his thoughts gradually taking over.
- Inverted for Revival, where ordinary humans try eating reviver flesh in order to become revivers themselves. In at least one case it works.
- The Saurians in Sigil (and the one who appears in Negation) take on beneficial attributes of whatever creatures they eat, including physical and mental traits and even information. Having long ago become the apex predators of their homeworlds, this power was forgotten and rediscovered when they went to war with humans and decided not to waste the corpses of their fallen foes.
- The Chitauri of The Ultimates (2002) can only shape-shift into the body of somebody by eating that person. Herr Kleiser threatens to do this to the Wasp, but is interrupted before he gets an opportunity.
- The X-Men villain Dirt Nap gains the appearance and powers of people he swallows. The victims can survive if he coughs them up within a certain time frame. For some reason, he can't do anything about the smiley face symbol that always appears. He also winds up stuck in the form of a rat for much of his history. Eventually, he becomes an ally to Generation X. He is even able to separate M-Plate back into the twins and Emplate by sucking them up and separating them, though this ends up killing him.
- In Wreck-It Ralph, Cy-Bugs become whatever they eat. In the beginning, a Cy-bug eats a gun and sprouts Arm Cannons. A Cy-Bug who starts eating the landscape of Sugar Rush becomes candy-coated. In the finale, a glitch-infected King Candy/Turbo is eaten by a Cy-Bug. Ralph then has a show-down with a terrifying glitch-infected King Candy/Turbo/Cy-Bug monster.
- The vampires in Daybreakers have to drink human blood or else they transform into subhuman monsters. Expanding on this, drinking vampire blood (even their own) causes the mutation to accelerate. And conversely, drinking the blood of an ex-vampire will turn the drinker back into a human.
- Attempted by the Millenians/Orga in Godzilla 2000. The aliens use Godzilla's DNA to regenerate and conglomerate into a Kaiju called Orga, which eventually tries to swallow Godzilla to complete the process. During the attempted swallowing, Orga takes on more and more attributes of Godzilla.
- In Men in Black, the alien roach skins a farmer near its crash site and wears him to pass as human. As the film wore on the skin decayed more and more, making the impersonation all the creepier. They call it an "Edgar-Suit".
- The vampires (or "NetherFolk") in Nether Beast Incorporated eat human meat for survival and recovery.
- Wesker in the film Resident Evil: Afterlife needed to feed on uninfected humans to keep from going the way of the boss monsters in the last three films.
- This is how The Thing (1982) works. Specifically it's a shapeshifting alien that eats animals (dogs and humans in the movie) and then mimics their appearance and memories to become an exact replica.
- In Agatha H. and the Clockwork Princess, it's mentioned in a footnote that that universe's counterpart to Brillat-Savarin was eaten by a monster who misinterpreted the page quote and decided that he wanted to be Brillat-Savarin. And then, after doing so, it began publishing works under his name.
- This is one of the secrets of the Inhumi in Book of the Short Sun; feeding off humans is the only thing that makes them intelligent and capable of having personalities.
- In Everybody Loves Large Chests, the protagonist has to eat a few individuals of a species before figuring out how to shapeshift into them.
- The Nightmare's dream attack on Harry Dresden in Grave Peril is a version of this — having consumed much of Harry's magic, the Nightmare gains the ability to both use that magic himself and impersonate Harry by taking on his appearance.
- In Harry Potter, Polyjuice potion requires a bit of the person being impersonated as an ingredient. The good news is that this only takes something small, like a hair, to work. The bad news is that the person has to still be alive when the bits are taken. So anyone attempting long-term impersonation has to keep the original alive and captive, which happens to Alastor "Mad-Eye" Moody when Barty Crouch Jr. impersonates him.
- Something less creepy: "If the saying 'You are what you eat' is really true, then Lord Voldemort is a unicorn."
- A nightmarish version occurs in one of the novels in Andrey Livadny's The History of the Galaxy books, where a human ship arrives on a habitable world that does not appear to have any animal life. Then the humans get picked off one by one by strange shapeshifting creatures. In the end, all humans have been consumed, but the shapeshifters also absorb their memories along with their DNA and begin to think of themselves as human, not understanding why they are suddenly amorphous blobs able to form into anything they wish. Another novel has a scout ship re-discovering the planet only to realize the shapeshifters are intelligent. The captain of the scout ship doesn't care and wants to exterminate them in order to claim the planet and retire on the fortune (habitable worlds are extremely valuable). The protagonist manages to get rid of the captain and leave, wiping the location of the world from the navigation computer, so the creatures can live in peace.
- Yet another novel reveals that the shapeshifters are the result of an ancient experiment to create immortality. It worked. The resulting creatures went out of control and began consuming all the surrounding fauna, eventually leaving the half-dozen shapeshifters the only non-plant organisms on the planet. The same experiment on another world had slightly better results.
- In Human Nature, one of the members of the Family is a shape-shifter who can imitate any animal he's eaten part of, including humans. If he does it while they're alive, he can also gain their memories.
- In the original Brothers Grimm version of Little Snow-White, the wicked stepmother attempts to invoke this when she believes she is eating the lungs and liver of her beautiful stepdaughter.note
- In Mistborn, the kandra are creatures who can take on the appearance of a person after consuming their bones. They do this for humans as a service for a very specific kind of payment. They are literally contractually obligated not to kill humans, though. Their employers provide the corpse.
- Particularly skilled kandra can assume someone's form without having eaten them. They still need a skeleton, though, since they're basically Blob Monsters in their true forms and don't have any rigid bones of their own.
- Parodied in G. K. Chesterton's The Napoleon of Notting Hill, where an extreme British nationalist who preaches cannibalism of non-British people discovers, to his horror, that this trope is true, and therefore he is now slowly turning into an Italian organ-grinder — which is apparently the only type of edible foreigner he could find in London.
- Oliver Twisted: Whenever Fagin/Ankou eats a soul, his appearance temporarily shifts into that of his victim, seeming to physically visualise the victim's last moments upon having their soul taken, before he burps and returns back to normal.
- Patternist: The master Biomancer Anyanwu learns new Voluntary Shapeshifting forms by consuming a small amount of flesh or blood from unfamiliar animals. This also lets her add traits from those animals to her own body, such as an eagle's vision or a dolphin's improved ability to process oxygen. Eventually, she learns to copy people so precisely that she can have children who are their genetic descendants.
- Phantoms features an Eldritch Abomination that absorbs the memories of the humans it eats. As a consequence, it has come to believe that it is the Devil, since that is what many of its victims thought when they encountered it and were consumed.
- Demons in The Riftwar Cycle gain knowledge, abilities, and to some extent form from the other demons they eat.
- Tofu from Super Minion can sort of mimic someone's form just by looking at them, but it's easier to get the fine details just right if he eats a corpse. He can also figure out how to incorporate physical powers from corpses he eats into his own form.
- In The Throne of Bones, ghouls' tendency to assume the appearance and identities of those they devour — even to the point of forgetting that they're ghouls — is pivotal to most of the stories.
- In the Urban Dragon series, ghouls gradually turn into an average of the creatures they consume. Eating animal meat turns them into bestial monsters, while eating humans allows them to keep a human appearance and intelligence. One ghoul, who works as a mortician, is noted for being exceptionally beautiful because she is able to select her meals from the most attractive corpses.
- Hive from Agents of S.H.I.E.L.D. gains the memories of everyone he consumes, and can also take on their appearance.
- Jasmine, on Angel, who had to eat people in order to heal herself and maintain her human appearance.
- The demon group "Brotherhood of Seven" in season 1 of Buffy the Vampire Slayer had to eat the heart and brain of a human/s every seven years in order to maintain their disguise.
- When the Wolf from the fairy tale swallows the protagonists' grandma whole in Charmed, he automatically shapeshifts into her appearance, as a distillation of the original story.
- Doctor Who: In "Smith and Jones", the plasmavore already looks human, but has to drink human blood in order to scan as human.
- In the Fear Itself episode "The Eater", the eponymous Serial Killer Dwayne Mellor consumes parts of his victims in order to assume their forms. It works.
- From Dusk Till Dawn's version of vampires, culebras, have this as an ability. After drinking someone's blood (as well as their soul, based on Carlos' description), they can shapeshift into that person's form, complete with their memories and the ability to mimic their attitudes and behavior.
- Ghoul: The ghoul takes on the form of its last victim. Initially, it looks like Ali Saeed, but later starts impersonating other people, causing no small amount of paranoia among the Dwindling Party.
- The Outer Limits (1995): In "The Voyage Home", there's a shapeshifting alien which assumes the form of the people it eats.
- In one Sesame Street sketch, Cookie Monster goes on a cookie binge and falls asleep. In his dream, he is confronted with a former monster who loved cookies so much that he literally became a Monster Cookie.
- A two-part episode on Sliders involved the logistics behind moving a select portion of the population before their Earth is destroyed. It turns out that the man in charge has to ingest brain tissue from compatible donors due to treat a fungal brain infection. Injecting the tissue causes him to temporarily morph into the person while the donor goes into a coma. The list of people he handpicks to move on to the new world are all compatible; he intends to use them all to stay alive.
- There's a type of monster called ghouls - scavenging monsters that eat corpses and take on the memories and appearance of the last person it ate.
- Leviathans don't need to eat you to take your appearance. All they need to do is absorb a bit of your DNA (they can even pull it off using hair fished out of a shower drain), which allows them to shapeshift into a perfect copy of you. However, as Extreme Omnivores with limitless appetites, they'll quite eagerly eat you anyway if they get a chance.
- German Band Knorkator has the song "Ick wer zun Schwein" (I turn into a pig). It's about a man who ate a really large steak all by himself, which causes his DNA to be rewritten and turn him into a pig.
- In the music video for "Best Friend" by Foster the People, a supermodel devours other supermodels whole and alive and so she can take on desired aspects of their appearance and further her career. Over the course of the video she eats a woman for her beauty mark, another so she can have her legs among others. However over time with all the clashing body proportions she starts to look less like a beautiful woman and more like a spindly, freakishly tall, disproportioned alien. By the video's end she winds up barfing up the dress of a woman she had eaten, chokes on it, loses her newly acquired features, and dies on the catwalk.
- In the Cool Kids Table game Bloody Mooney, Mooney briefly assumes the form of Keri's mother (who he ate the previous night) while chasing the trio. Fortunately this doesn't phase the teens while fighting it.
- Ghouls in Less is Morgue are able to transform into anything they've eaten recently. Riley uses this to help a regretful ghost process his daddy issues.
- Anima: Beyond Fantasy: The D'Anjainy play this overlapping with Face Stealers, as they skin the face of the person who want to copy and place it over theirs to look as the previous owner of that face. The game says nothing about what happens to the unfortunate victim, by the way.
- Call of Cthulhu. The Consume Likeness spell allows a sorcerer to take the form of a dead person by eating their body.
- Chronicles of Darkness: Spirits commonly consume other Spirits for their Essence; if the meal isn't a spirit of the same type or of a type that makes thematic sense for the spirit to be eating (like a wolf spirit eating a rabbit spirit), the meal's Essence can infect and alter it, sometimes to the point of creating a hybrid "Magath" mishmash of concepts.
- The Dresden Files: As in the source material, some of the shapeshifting powers work like this — notably Mimic Abilities (and, it's at least implied, to a lesser extent Mimic Form). The former is even explicitly called out as "a bit of an "evil people eater" power" by Will.
- Dungeons & Dragons: Mongrelmen are descended from beings that had this ability. Mongrelmen themselves are Mix-and-Match Critters comprising aspects of all the humanoid creatures their ancestors consumed... and a few clearly non-humanoid for good measure. At least, that's one version of their backstory. The more common one is simply that they are what happens when you breed together enough humanoid races.
- Exalted: Lunar Exalted can take the form of any creature whose heart's blood they've tasted.
- GURPS: Skin-Changers from Monster Hunters are embodied spirits who can shapeshift into any animal (including humans) by wearing their skin. Unlike the Men in Black example, Skin-Changers are clever enough to preserve the skins, and save them in jars when they're not being worn.
- Warhammer 40,000: Several alien species have this trait, but the two most prominent are the Kroot and the Tyranids:
- The Kroot are a race of humanoid avians which evolve primarily by eating other beings and absorbing their genetic traits, with the various subspecies (Krootox, Kroot Hounds, Knarlocs...) being Kroot who ate too much of a certain species and are now stuck in that role. In fact, the reason Kroot are able to build spaceships is because they ate a bunch of Orks and absorbed the Mekboyz' genetic memory. Kroot also have a taboo against eating Tyranids to avoid creating some sort of horrendous feedback loop (a fear the Tyranids do not share, though the Imperium was too busy glassing the planet to figure out the full extent of the consequences).
- Tyranids are the stereotypical Horde of Alien Locusts who use Organic Technology, so their main approach to warfare is consuming new species and splicing in genes from consumed creatures to mutate new subspecies that fit specific roles.
- There's also an alien species called the Simulacra, which in their natural form look like mostly featureless humanoids. They can mimic the appearance of other humanoids by eating their brains, which also grants them the victim's memories. The knowledge and ability to maintain the form vanishes once the brain is digested, forcing them to find new victims every so often. They're also the only one race that plays this trait fully straight, as neither Kroot nor Tyranids can directly metamorphose into their victims.
- On the Verge, or the Geography of Learning has an unusual example Played for Laughs: A cannibal gets confused about his own identity thanks to ingested memories.
- Arknights: Consumption of Seaborn flesh - whenever intentional or accidental - will start to mutate the individual into a Seaborn. Captain Alfonso and his first mate Garcia in "Stultifera Navis" were transformed due to eating Seaborn for sustenance after they ran out of supplies, "Mizuki & Caerula Arbor" implied that Mizuki and Highmore became Aegir-Seaborn hybrids due to being fed food laced with Seaborn cells and Irene was turning into a Seaborn due to accidental ingestion.
- Chimera Beast has the Villain Protagonist as one of a Horde of Alien Locusts appropriately known as Eaters. By using your bite move on organic enemies, you can gain similar abilities to them.
- Dead Space 3: Feeders are creatures that have become Necromorphs because they were desperate enough to eat Necromorph flesh.
- The Elder Scrolls: Some vampire bloodlines have an unusual inversion of this trope. The longer they go without feeding, the more powerful they become, as well as becoming more monstrous in appearance, which tends to give away their vampiric nature. Further, they risk going irrevocably insane and feral if they go too long without feeding, becoming "Bloodfiends". The vampire bloodlines the Player Character can join in Oblivion, vanilla Skyrim, and Online function in this way. (The Dawnguard DLC for Skyrim changes up the functionality, giving access to the Vampire Lord Super Mode form instead.)
- Kirby can assimilate the special abilities of many of his enemies by swallowing them. Fan works often exaggerate this to Kirby assuming the characteristics of anyone and/or anything he eats.
- [PROTOTYPE]: Alex Mercer's disguise ability works like this. When he consumes the individual, he uses their genetic code to reproduce their appearance and voice while their memories are directly absorbed.
- The Visitor and its sequels focus on a small, slug-like alien that takes on the characteristics of the animal it eats. By the end of the second game the alien has so many abilities, there are a total of six endings based on which of the abilities you use to destroy the trailer owner's wife.
- If the Emperor Had a Text-to-Speech Device: Rogal Dorn asks the Emperor if he's familiar with the phrase "you are what you eat." Because he's apparently acting like an ever-growing pile of screaming psychic children.note
The Emperor:Wow Rogal. Way to bring down the fucking hammer.
- Watermelon: A Cautionary Tale: Jimmy learns the hardway: eat watermelon seeds, become a watermelon.
- Brawl in the Family: This appears as a Running Gag for Kirby. He inhales something or someone and (usually) obtains that victim's appearance, quirks and/or abilities.
- Charby the Vampirate: Changelings change by absorbing whomever they are changing into, taking on their memories and often seeking their previous form since they appear to have gone missing without realizing that they've killed someone in a very Body Horror fashion whom they probably considered a friend.
- Demon Eater: This is the main way of growing in the demon world. Demons must eat demons, or be eaten themselves.
- Drowtales: This is apparently the method that Vel'akar (sentient demons) use to appear more humanoid, since by default they resemble Blob Monsters. Khaless, Snadhya'rune's protector twin, is actually such a demon that devoured the original Khaless and seems to have taken over her role, and she later inflicts the same thing on Lulianne and Sael Dutan'vir and is able to pose as them without anyone noticing.
- Sluggy Freelance: Zombies have to eat the brains of the living or they'll lose their own intelligence.
- Stand Still, Stay Silent: The Merger of Souls ghosts have their appearance influenced by the souls they absorb. It's especially noticeable because the only ghosts that have this property are human, yet those that have absorbed other souls look like Mix-and-Match Creatures.
- SCP Foundation, SCP-974 ("Treehouse Predator"). While in its standard form, after SCP-974 kills and eats a child of age 6-12 it will change to that child's form over a period of 10-12 days. In its enhanced form it can kill and devour adult human beings and take their form in a short period of time.
- The Grim Adventures of Billy & Mandy: In the fairy tale episode, Pinocchio wants to be a real boy by eating human flesh, specifically Billy's.
- Invader Zim: In "Dark Harvest", Dib tells Zim that he knows he's an alien because humans don't have a squeedlyspooch, and Zim doesn't have any normal human organs. Zim's solution is to stalk his classmates, steal their organs, and stuff them inside himself. This trope is played with, however, in that Zim doesn't so much eat the organs as teleport them out of his victims' bodies. At one point, the nurse tells Zim he's extra human for having multiple organs, while Dib almost gets hauled off by the MIB for missing some.
Dib: I suppose you have a heart?
Zim: Six of them.
Zim: Large and small.
Zim: In three different colors.
- Ollie! The Boy Who Became What He Ate is a Canadian cartoon about a boy who turns into whatever healthy food he eats.
- Stroker and Hoop: A group of cannibals steal and consume the vestigial organs of humans under this reasoning ("Eat a human, be a human!"). After Stroker pisses them off and they decide to cannibalize him completely, he tries to convince them that, as a guy who eats burgers, he is in fact a burger and they'd be violating their own beliefs. They ignore him.