Vampires seldom reflect on the emptiness of their unlives. But think of the potential limbo victories!note And it's not just her and that one vampire; there's an entire masquerade ball of them!
There are many things that go bump in the night, secure in the knowledge that their unholy powers can trick the human eye into blindness, allowing them to live among and prey on humanity with impunity. But their supernatural (and at times inherently evil) nature means that no matter how complete the deception, they can never truly hide what they are. They may fool the mundane senses, but not the spiritual ones; inanimate objects, animals, children, The Empath or spiritually touched people can sense and see through the deception and cause a Glamour Failure. The Hunter and mundane heroes wise to these evil tells will be sure to use them to ferret out the villain; directors also love to work them into The Reveal when the creature's victim finally puts two and two together. More tragically, a hero under the effects of The Virus will usually have the full emotional impact of it sink in when she can't see her reflection.
These flaws in their façade are usually mixed and matched. So your mileage may vary depending on the critter:
No reflection (usually reserved for vampires and The Soulless). Genre Savvy characters noticing a lack of mirrors (or several broken ones) will have this same effect. Depending on the setting, this may include not appearing on film and/or digital cameras, or being inaudible on telephone or recording.
True reflection (Fae or other glamour users will usually reflect their true image). A modern variation has the true form of glamour users revealed by a security camera, since glamour meant to fool human minds won't work on a machine.
Pointed Ears. A staple of vampires, fairies and Vulcans (though these last ones aren't evil, we promise [unless it's Evil Spock, but that's just a technicality]). For vampires, it's presumably to mimic a bat's large ears... or it could be done to up the Ho Yay factor.
Sunlight burns/weakens/makes themsparkle (not restricted to vampires, any strongly evil or supernatural creature will react to sunlight like a marshmallow in an oven).
Holy objects burn/repel (pretty basic, anything holy aligned will repel evil, may be culture specific and/or depend on having a pure heart or strong faith).
Variation: The object itself need not be emblematic of the church or God, it just needs to be something the wielder places his faith within.note One story had a man ward off a vampire with a credit card this way. The Faans webcomic had the protagonists subdue a vampire with the Vulcan hand signal.
Anything made of silver burns vampires in Hellsing.
Seras Victoria burns herself when handling silver bullets in the second episode of the anime. Later in the same episode she jokes about burning herself with silverware. It's not clear if this is the case in the manga as well, since she always handles her silver bullets while wearing gloves.
Subverted in the Ghost in the Shell: 2nd Gig episode "Trans Parent", in which Batou is convinced that a young girl can see through his thermoptic camouflage somehow. He's wrong — she's blind.
The wolves in Wolf's Rain use some kind of glamour to appear human, but humans can occasionally see through it. There's also the matter of the wolf tracks they leave behind. There are also a couple of instances where the wolves look human but cast wolf shadows, though this only happens when humans aren't looking.
On Pokémon, the character Duplica has an inexperienced Ditto that can transform, but retains its own facial features, (such as they were). Her next appearance has a second, undersized Ditto, named Mini-Dit. This one could transform, matching everything but size. This led to appearances by the likes of mini-Onix and mini-Ursaring.
Medusa in Soul Eater has a tendency to form slit-like pupils when feeling particularly sinister, often accompanied with a Slasher Smile.
And one of those 'snakes' of hers forming a forked tongue on one occasion. The above is all the more disturbing when she possesses a little girl.
Midway through To Aru Majutsu no Index, Touma suddenly finds himself in a bizarre world where everyone's appearance has been swapped without anyone else noticing, leaving him the Only Sane Man for much of the time. However, photographs are not changed from Touma's perspective (though even television broadcasts are). He identifies the spellcaster responsible by how their appearance in person is the same as in a photo.
A variation of this occurs early on in Harukanaru Toki No Naka De manga and TV anime. A female ghost, given a beautiful human form by the Big Bad, seduces young men who come to visit her, devouring their souls. When Yasuaki is sent to investigate the case, she tries this tactic on him, only to be informed that he has no emotions that would allow him to appreciate her beauty, and therefore sees her just as what she really is (a skeleton). She does not take it well...
His classmates' apparent obliviousness is eventually explained: people with some form of demonic heritage aren't uncommon at all, even in the world of exorcists. The big issue with Rin isn't that he's the son of a demon — it's that he's the son of Satan. Everyone else is justified by the fact that only someone with a Masho (demon wound) can see demons. That, and his hair is long enough that his pointed ears could go unnoticed...not to mention not many people are going to be staring at someone's teeth.
An invisible Robeast in Voltron is betrayed by the fact that it leaves giant footprints, turns visible when struck by an attack, and inexplicably starts casting a shadow towards the end of the episode.
Once she gains control of it, Sailor Neptune can break illusions with her Submarine Mirror.
Since her disguise spell takes concentration to maintain, Filia Ul Copt will start dropping aspects of her disguise (such as revealing her tail) when she's emotionally strained.
Junji Ito's Tomie shows up on film with extra eyes, mouths, or faces in strange places. She also directly manifests these defects when under sufficient stress — suggesting that she's diseased or a monster seems enough to trigger her physical instability.
Maguro, Agitaro and Furiyo's Humanization Transformations are incomplete, leaving them with literalfish faces◊.
Octopus Nakajima reverts back to his true form at random.
Maki's Humanization Transformation is also imperfect, rendering her mouse-sized. Late in the manga, however, she perfects it.
In the Marvel Universe, there have been various ways over the years to detect the shapeshifting Skrulls, including superhuman senses, telepathy, magic, and various devices. Also, death. However, as of the Secret Invasion storyline, the Skrulls have figured out ways to trick telepaths, magic users, and super-senses, leaving technology (e.g. 3-D Man's special goggles) and improvised tactics (e.g. Ms. Marvel shooting a whole crowd with a low-level energy blast strong enough to knock down the humans and leave the Skrulls standing).
And then Reed figures out a way to reveal the Skrulls anyway. Guess he's not so useless after all.
Komodo from Avengers: The Initiative must maintain some level of consciousness to keep her transformation, otherwise she reverts back to her true form. She does exactly this in one issue when she accidentally falls asleep in front of her teammate Hardball. Inverted in that she's an attractive young woman in her true form, while transformed she's a lizard...thing. But played straight in that in her human form, she has no legs.
An interesting example is Mrs. Vashti, a.k.a. "Spell Syrin", one of the teachers of PS238, and a former superhero. Rather than bother with official clothes, she just walks around in her spandex-tastic superhero outfit all the time, and uses Glamers to appear demurely-dressed to others. The reader, however, usually sees her as she really is, and a couple of mystically talented students have also demonstrated the ability to see through it. More interestingly, when mirrors appear, they show us what she appears like to others, in a direct inversion of the classic "The mirror tells the truth" cases above.
In that vein, Girl (Varied Number) from the Top 10 comic book series uses her color control over her android body to fake clothing. Too bad her commanding officer, a sentient dog, is colorblind. Punching ensues.
In Usagi Yojimbo, this is the manner in which every disguised supernatural creature is revealed. Stan Sakai grounds much of his work in the actual mythology and history of Japan (see below).
Claudine Renko (aka, Ms. Sinister) has some shape-shifting abilities (as does Nathaniel Essex himself). After capturing X-23 and Gambit in the Songs of the Orphan Child arc of Laura's solo series, she tries to put the moves on Gambit by taking Laura's form. She completely fails to match Laura's mannerisms and speaking patterns. Gambit isn't fooled for a second.
Megamind's holo-watch allows him to look like anyone it scans beforehand. However, he, apparently, forgot to waterproof it. It also shuts off if he bumps it by accident.
Also, while not noticed by any of the characters, his eye color remains the same no matter which form he takes.
In Wreck-It Ralph, Vanellope's glitching spreads to whoever she touches, causing them to glitch out until released. When she does this to King Candy, it exposes his true identity as Turbo, which was hidden by the King Candy skin.
In The Incredibles, Violet can make herself invisible, but when hiding in a river, a rather clever Mook throws some sand upstream of her last known position, allowing the distorted flow to reveal her.
Films — Live Action
In John Carpenter's They Live! (1988), aliens use a mind-controlling satellite signal to appear human, cloaking themselves from the eyes of Mankind while they take over governments and corporations. A resistance movement forms when someone creates special sunglasses that can filter out the signal before it reaches the brain and allows the wearer to see the aliens as they truly are. The film ends with the resistance dying but not before destroying the signal's ground station, breaking the Masquerade.
The Shadow (1994) with Alec Baldwin as Lamont Cranston a.k.a. the mysterious Shadow, the titular character of this movie screen comic book adaption. His powers of deception, mind control and telekinesis are clearly psychic, the result of a Training from Hell by an ancient mysterious Asian mentor. Only two people can see through his hypnotic deception: his arch-enemy who has similar mental powers (and who can hide whole buildings from the eyes of passers-by), and the professor's blonde daughter who is a latent psychic herself and who catches a glimpse of The Shadow when she meets Cranston.
Cranston also lands himself in hot water twice when the villains circumvent his ability to cloud mens' minds. The first time happens in Dr. Lane's lab when one of Shiwan's men begins shining a flashlight around the room, discovering him when the light falls on him and makes him cast a shadow. The second time happens when he tracks down Farley Claymore to a pressure testing chamber, thinking he's been brainwashed into helping Shiwan; the latter starts filling the tank with water, and spots Cranston by looking for signs of water flowing around a person's legs. He ends up getting shot on both occasions.
In X-Men, Mystique's shapeshifting isn't quite perfect. Her eyes flare yellow if she loses her concentration, for example, and she can't quite mimic the smell of others (making her particularly vulnerable to Wolverine's sense of smell). Also, she can't seem to shapeshift out the scars Wolverine leaves on her.
Early Terminators (mentioned in The Terminator) could be recognized easily due to their rubber skin. Because of that the T-800 has an organic coating, but can still be recognized by man's best friend.
The T-1000 in Terminator 2: Judgment Day could imitate anything it touched, within certain limitations. However, when it's too hot, its mimicking technology got a bit... twitchy. Beyond that, your only clues are his precise movements from the Uncanny Valley Acting School, and a Bluff the Impostor moment when he's imitating John's foster mother. The dog trick works on the T-1000 as well. Probably because it can imitate shape but not smell.
In Phantom of the Paradise, Swan's lackeys always make sure that he's never photographed or filmed. It's revealed that years ago he made a Deal with the Devil that allows him to never age; part of the price is that this trope applies to any pictures/film taken of him since the pact was originally made (and videotaped — the tape is his Soul Jar).
In the Blade movies, the Glamour Failure ends up being needed. If you are a certain vampire's pet, you gets a tattoo so other vampires knows not to eat you. This helps (and oddly hinders) Blade. And relatedly, despite getting all the good bits of vampire powers in his origin (durability mostly) he cannot detect if his adversary is a human with fake pointy teeth. This also comes back to bite him on the ass (pun intended).
The page image from Van Helsing shows one of the common ways in which vampires can experience this — lacking a reflection in a mirror. Those paying close attention can see the later Oh Crap moment coming—not only is Dracula not showing up in the mirror, but neither are the other couple hundred people in the room.
The same trope of vampire lore was parodied in Dracula: Dead and Loving It, where a big dance scene ends up being ridiculous when seen in a mirror, particularly when Dracula is spinning the woman in the air.
In the 1986 remake of The Fly, Seth Brundle realizes just how badly he has already been transformed when the computerized teleportation pods refuse to recognize his voice.
Blade Runner: Replicants are identical to humans. The only reliable way to detect them is the Voight-Kampff test which monitors answers and subtle physical response to emotional questions.
They're immune to both extreme heat and extreme cold, but good luck detecting them on this unless you don't care about having real humans survive the test... Dunk the Witch anyone?
Apparently Tyrell corp never thought of installing some kind of integral tracking beacon inside, especially after people died because of rogue replicants, especially with them being so hard to identify and track otherwise.
And apparently even though every scale of an artificial snake has the manufacturer's serial number on them, no-one thought about putting anything similar to much more dangerous humanoid replicants.
The humanoid replicants, being sentient and intelligent, will just find a way to remove them. Also, it is stated in the book that the company who makes them are trying to make replicants that are indistinguishable from humans.
In Galaxy Quest, Fred Kwan had been making eyes at the Starfish Alien that's disguised as a pale-looking human. Eventually, the two finally kiss, and she lets some of her tentacles out from beneath the illusion. Subverted in that, instead of repulsing and frightening him, it seems to turn him on even more, and they get right into it. Though bystander Guy is repulsed.
In Thor, Loki's true nature as a half-Frost Giant is revealed whenever he touches another member of his race or is exposed to their technology. Played with in that HE didn't even know his true form until the first time this happened.
Played with in Interview with the Vampire. Louis steps under a bright light to convince Daniel of his true nature, but after a moment of shock, Daniel simply rationalises that away. Eventually he is forced to use superspeed to drive the point in.
In Breaking Dawn of the Twilight series, when the vampiric Bella meets Charlie for the first time after having been turned Alice tells her that she should wear contact lenses so Charlie doesn't notice the difference in her eye-colour, but the lenses would only work for a few hours before the venom in her eyes disintegrated them, after which she'd have to change lenses.
In the Modern Tales of Faerie one of the characters in Valiant, Ravus (a troll) explains that no glamor is perfect and some trait of the faerie remains e.g cloven hooves or tails or backwards feet.(in his case he still has black and gold eyes). In Tithe Kaye see's her true unglamored reflection in a mirror briefly later explained when Roiben said glamor could be seen through out of the corner of your eye
The Discworld gods, despite their reality-altering powers, cannot change their eyes. Said eyes always reveal something about their true nature.
In the novel Reaper Man, there's a scene where a child sees Death in his true form as a skeleton man, thus showing that his power is weakening, whereas Death is able to make adults see him as human (or they at least convince themselves they aren't seeing a skeleton). Blacksmiths (even Death's horse needs shoeing) use blindfolds when the time comes. Knowing Death is hanging around is a pretty scary proposition.
Death's glamour relies on a forced augmentation of the normal human Weirdness Censor: he convinces a person that they cannot possibly be seeing what they are, and so the brain makes up imagery that fits this impression. People who have a reason to see through the illusion or who already know what they're looking at aren't fooled.
Also wizards, who are trained to see things as they really are (much harder than seeing what isn't there).
And children — the aforementioned child could see his true form because really young children have no Weirdness Censor, so she doesn't know that a skeleton person is impossible.
In Lords and Ladies, those who get close enough to the elves or who are wearing or carrying enough iron can see through the glamour they cast and notice that they look... well, alien. Dwarfs, trolls and animals (such as everyone's favourite sentient orangutan, The Librarian) get this ability for free. Dwarfs and trolls go into "crush, kill, destroy" mode on sight of an elf. Whether this is an ability that all Dwarves are born with, a side effect of their intense hatred of elves, or a result of the armor they're typically clad in is up for debate.
The Glamour of the Elves is an active power they must concentrate on to keep it working. If you knock an elf unconscious, the Glamour vanishes.
Elf glamour otherwise works like that of Fair Folk. They don't see in the usual way, and iron tends to mess up their perception. If you're wearing iron, you're pretty safe; if they're wearing iron, they're screwed. Of course, the resident blacksmith has no trouble with them. Granny also notes that modern Discworld residents, like those in Ankh-Morpork, have "iron of the mind": in other words, they're so jaded and skeptical that glamour wouldn't affect them; thus why elf encounters tend to stick to the more-rustic Ramtops.
Computers — whether they run on magic like Hex or not — aren't easy to fool in any of Terry Pratchett's works; even if it's just a throwaway line, they will see through glamour and respond appropriately. Specific examples include a military base's automated security system raising the alarm when Death and company enter an off-limits section in Good Omens, or a computer chitchatting with Santa Claus in a short story.
In Nathaniel Hawthorne's story Feathertop, the title character is a scarecrow with a pumpkin for a head who, due to a witch's spell, is made to appear as an elegant nobleman. When he first goes into public, adults are praising him, but it's mentioned that a small child "keeps babbling about a pumpkin." Later, Feathertop sees himself in a mirror and realizes he's not human and can no longer live with himself.
In Robert Bloch's story "Shadow from the Steeple", which is a sequel to H.P Lovecraft's "Haunter in the Dark", the protagonists confronts the man he believes to be possessed by the god Nyarlatotep, noting that his skin has turned darker. The man explains this has been caused by exposure to radiation (he was a nuclear physicist), but when the protagonists doesn't believe him, he turns off the lights, causing his body to glow with unnatural light, and causing the protagonists to die of heart attack.
A variation of this shows up in Mike Resnick's science fiction novel Santiago: A Myth of the Far Future, although that is more due to a lack of knowledge on the villain's part. In order to kill the bounty hunter Sebastian Nightingale "Songbird" Cain, the assassin Altair of Altair somehow makes him hallucinate that he is back on his home planet of Sylaria being asked by someone he cared about to help her across a brook (as a lure to get Cain close enough to Altair for her to stab him). At the last moment, he shoots her and tells her corpse, "There aren't any brooks on Sylaria."
In the Warhammer 40,000 universe, daemonhosts (a daemon sealed in the body of a human by means of occult rituals and symbols) generally resemble the person whose body they're possessing, but with distinct physical changes that identify them for what they are. For example, in the final Eisenhorn novel Hereticus, Inquisitor Eisenhorn notes that while the daemon Cherubael has made all the usual physical alterations to its host body - small horns, glossy golden skin, blank eyes, and claws - the daemonhost still bears a chilling resemblance to his old friend Godwyn Fischig.
In Dan Abnett's Brothers of the Snake, a squad of marines finds themselves fighting foes that can only be seen with the naked eye; all their equipment will not recognize them. They bare their faces and win, though several die because of the vulnerability. Later, a Chaos daemon infiltrates a Chapter House. After one Marine recognizes it and kills its host, it escapes, but a second one manages to recognize it. (It also manages to make the rest of the House believe that the first Marine was raving in his cell, but the second one manages to see that in fact, the man is sitting there quietly, and talks with him.)
Another WH40k example: in the Gaunt's Ghosts novel Ghostmaker, an Eldar Farseer is manipulating the memories and perceptions of the Tanith First and Only, making them believe that they are back on their doomed homeworld, fighting for its survival. The illusion isn't perfect, however, as several characters get the sense that something is wrong, and eventually the glamour fails when mildly psychic teenager Brin Milo looks at a disguised Eldar warrior through the appropriately-named "Mad" Larkin's sniper scope, revealing that the tall, thin "Tanith" with white and red hair is in fact a Dire Avenger Aspect Warrior.
In Stephen King's story The Ten O'Clock People (found in Nightmares and Dreamscapes), only very light smokers can see the "bat people" who are steadily taking over. Non-smokers and heavier smokers alike simply see humans where the titular group sees the monsters.
Although in Jonathan Strange & Mr Norrell, The Fair Folk are The Beautiful Elite, in some tales from the story collection set in the same universe The Ladies of Grace Adieu and Other Stories, they and the other creatures they consort with are shown as actually being monstrous and their fabulous palaces are similarly an illusion hiding squalor.
There are subtle hints in the few descriptions of Lost-hope in Jonathan Strange & Mr Norrell, for example, there are tapestries made of skin. It's never commented on and is probably quickly forgotten by the average reader.
Several stories in C.B. Colby's Strangely Enough feature animals detecting the unusual and supernatural. "Black Knight of Canterbury" has a dog detecting the passing of a ghostly knight, and in "The Frightened Dog" the title animal detects the approach of a weird threat before the humans he's with do.
Colby: Perhaps it is true that dogs can see what we cannot.
Rod Serling's The Twilight Zone anthology, story "The Avenging Ghost". A Great Dane named Duke is able to detect and see the ghost of his dead master before the humans with him can.
The main character of Peter Schlemihls wundersame Geschichte ("Peter Schlemihl's Remarkable Story")sells his shadow in exchange for great wealth, but is shunned by the rest of society for not having a shadow.
Rather inverted in The Outstretched Shadow by Mercedes Lackey and James Mallory. In their true form the demonic creatures known as the Endarkened possess red skin, horns, and catlike yellow eyes. Neither the Endarkened or their works/creatures/spells can withstand the touch of a Unicorn even were one chaste and celibate enough for a unicorn to let touch it without trying to kill them. So when a woman with red skin, horns, and catlike yellow eyes is cowering away from you against a unicorn you personally know (who is sitting there rather calmly and looks more annoyed with you than her) then it is clear that Something Strange Is Going On.
While her whole glamour was probably much more extensive than that, Lena in Night Watcher is outed as a vampire when her lover notices that she reeks of blood as soon as her mind control fades.
Vampires in Sergey Lukyanenko's World of Watches can glamour the minds of humans to hide themselves from sight. This does not work on Others, who can easily see through these mind tricks. The only way for a human to see a hidden vampire is to look at a reflection, as glamour only works in direct line-of-sight.
Video cameras work fine as well.
In the Twelve Houses series, moonstones burn the skin of and temporarily take powers away from (most) mages, such as showing a shapeshifter in his/her true form. This is a problem where mages aren't liked very much and gets the heroes in big trouble on occasion. Senneth is powerful enough that she actually wears moonstones, though she is weakened by them.
Mac from the Fever Series can see through any Fae's glamour. It's just one of the reasons they're so eager to kill her.
In a series as heavy on the supernatural as The Dresden Files, it's only natural for this trope to show up on occasion.
Vampires of the Red Court can be forced to drop their flesh mask by exposing them to True Sunlight, presumably because they can't maintain the focus to keep it up.
When a vampire of the White Court is about to be controlled by it's Hunger, silvery flecks show in their eyes.
White Court vampires also shine like porcelain when using super strength and their blood is pinker than human blood.
Faerie glamour can be seen through by a wizard's Sight or by using magical ointment on your eyes. Or you can just throw a nail at the fairie in question and watch them drop anything and everything to get away from it; even the strongest of faeries are vulnerable to iron's touch, which breaks through their magic and burns on contact.
As per the RPG rulebook, anyone with some magical talent gets some sensitivity toward others' supernatural natures, particularly with physical contact. While Muggles might walk right by a Red Court vampire without knowing about it, if a wizard did the same they'd at the least know something was up.
Most non-human creatures don't have souls, allowing a wizard who looks in their eyes to know they're not human, even if they can't tell exactly what they are.
In addition, wizards get an ability called the Sight, or the Third Eye, which allows them to see the true nature of whatever they are looking at, cutting through all illusion and glamer. However, you can never ever forget what you see with the Sight, and some of the things so seen can really screw with your mind. In one case, Harry takes a look at a particularly nasty critter, and its true form is so horrid that it gives him pause whenever it comes to mind up to three books later.
"The scaled people see what escapes the mortal eye," answered Pelias, cryptically. "You see my fleshly guise; he saw my naked soul."
An auditory example: in the third novel of Sentou Yousei Yukikaze, JAM prevented humans from perceiving machines. Rei realized this when he heard the noise cancellation system emitting anti-phase engine noise.
Ols can be identified by the mark of the Shadow Lord somewhere on there bodies, and by their form wavering once every three days. Inverted for Grade 3 Ols, whose shape shifting is perfect enough that they even die like humans.
At least once in Animorphs, an arrived Andalite is easily identified by the heroes due to her uncontrollable reaction to the food she's devouring.
In the TV series, controllers would often be betrayed by their habit of ear-scratching, but this did not appear in the books.
Also, when Marco morphs the wolf spider, he can see through the Chee hologram due to the spider's ultraviolet-capable vision. Before this, they key in on Erek because their dog morphs smell absolutely no scent at all on him.
Controllers can often be picked out by the revulsion and hatred in their voices and actions when they or someone else says "Andalite!" The kids can't reveal that they know what an Andalite is, so this is never used as a means of picking bad guys out of a crowd. In fact, a Controller once says "Andalite" to see if one of the kids was an Andalite infiltrator (the Controllers think they're looking for Andalites and not humans. The heroes would very much like to keep it that way.) but she seamlessly replies that yes, more lighting would be good.
In Paranormalcy, Evie's main ability is that she can see underneath paranormal creatures' glamours. She sees both their glamour and their real self.
The Dean Koontz novel "Twilight Eyes" features a protagonist whose psychic talent is to see the true nature of the shapeshifting creatures who live among humans. Interestingly, he had this ability from birth, so it took him many years to realize that hairy, wolf-pig people weren't just another ethnic group.
The antagonist of the Chanters of Tremaris series uses high-pitched Magic Music to cast spells of illusion to confuse or incapacitate those who hear it. This makes The Smart Guy, Trout, very useful, as he is partially deaf and can't hear high noises, so the spells fail to effect him.
Demons in Faeries of Dreamdark have two tells: they leave rooster-shaped tracks irregardless of the shape of their feet, and their humanoid guises never have the correct number of joints in the fingers.
Battlestar Galactica: Humanoid Cylons are very difficult to detect in isolation, but once more than a few get together it gets much easier as there are many copies, but only twelve "models". Their very existence is sniffed out this way by Helo in Season 1, and again by Kendra Shaw in the movie. Although five models exist as individuals without additional copies.
Then again, their spines glow during sex, which begs the question of how Baltar never managed to noticed this about Six?
The Tale of the Mystical Mirror: A woman who killed young girls in a ritual to keep herself eternally young and beautiful looked like an old hag (and so did her portraits) in mirrors. Hence why one girl wondered while visiting her house, "How can you be so vain and not have a mirror in your bathroom?"
Clearly taken from the folklore surrounding Transylvanian (Romanian) Countess Erzebet (Elizabeth) Bathory.
The Tale of the Captured Souls: A boy who stole people's youth to make him young forever looked like an old man in mirrors, pictures, and on video camera and was thus alarmingly camera shy.
Parodied on the US version of The Office in the episode "Business School." Jim is attacked by a bat and spends the rest of the episode faking vampire symptoms (garlic aversion, repulsion at Karen's cross, etc.). A dangerous game, knowing Dwight. Hilariously, this episode was directed by Joss Whedon.
The Smallville version of Bizarro looks exactly like Clark unless he's weakened or, later, exposed to sunlight, in which case his face will briefly flicker into a broken-glass-ish looking form that calls to mind the earliest comic book versions of the character.
A heroic example: Sam Beckett in Quantum Leap can be seen as he really is by the very young and animals, and sometimes by the insane, psychics, or people whose brain patterns are similar to his own. This also applies to his friend Al, who appears as a hologram that is normally invisible to others than Sam. Although due to real-life technical limitations, Al's hologramatic appearance sometimes casts shadows, his cigar smoke is affected by wind, his cigar smoke is visible despite the established rule that only things Al touches can be seen, etc.
One episode of Quantum Leap had Sam leap into the body of a madman who fancied himself a vampire, in order to protect a young woman from being killed by the vampire cult. Throughout the episode, Sam scoffs at the existence of vampires, until just before he leaps out; he finally sees a mirror, only to find that he has no reflection.
In another episode, a police psychic was able to see the real Sam after a while, meaning she is either insane or the real deal.
The TelenovelaLa Mujer en el Espejo ("The Woman in the Mirror") is about a homely woman who finds a magic mirror that gives her a beautiful appearance — but her reflection still looks ugly.
Buffy the Vampire Slayer. Buffy is supposed to be able to sense vampires magically, but this seems to be one of the Slayer powers that just did not manage to cross over. She still figures out two or three vamps because their fashion sense stalls at the point of time they, the vampires, first died. Dated clothes trumps weirdo magic-sense. There are a lot of vampires for whom this wouldn't work. At all.
Faith mentioned being able to tell if Angel was anywhere in a building, so it works pretty well for her. Apparently Buffy just has the sensitivity of a brick given the number of times vampires have been able to get right up to her (or on one occasion, make out with her) without being detected.
Some of the classic tropes also apply in the Buffyverse. Vampires, for example, don't cast reflections (prompting Willow to ask Angel at one time, "How do you shave?"). They also have a tendency to shift into their Game Face when emotional. Also, only children or people suffering from infections could see Der Kinderstod in the episode "Killed by Death".
In the Season 4 episode "Superstar", Adam sees through Jonathan's spell while everyone else is fooled; it is implied that this is due to his cybernetic nature. Adam himself believed it to be psychological, believing his utter certainty in his own reason for existence kept his mind from being fooled.
On Angel, a Genre Savvy vampire actually makes sure to keep all mirrors out of their surroundings to avoid this. Unfortunately for him, this, along with the heavy curtains and slightly suspicious behavior, causes the even more Genre Savvy Cordelia to figure out exactly what he is.
The Rakshasa are featured in Kolchak: The Night Stalker. This variation could appear as someone its victim trusted and/or loved; it could be repelled by the Swastika, which was a sacred symbol long before Nazi Germany co-opted it. This version was the direct inspiration for the D&D version, being vulnerable to a blessed crossbow bolt.
The first episode of Merlin uses the mirror variant with a vengeful crone who kills an esteemed guest of Camelot and takes her form.
It later shown to happen with every magical disguise. The reflection shows the true form. Though for some reason wery rarely characters are exposed via reflection. Usually it is only shown to clue the viewers in.
More broadly, sorcerers in Merlin are indistinguishable from 'Muggles' until they cast a spell, when their eyes flash gold.
Used several times in Supernatural. Mainly the true reflection variant (such as the Changelings, or the Siren). Occasionally, they'll thrown in the physical defect variant (the "flip-to-silver" eyes for the shapeshifters, a retractable layer of fangs for vampires.) But since most of the characters in the show hunt these nasties, they also have several tests, just in case. For starters, iron and holy water are pretty good indicators that a baddie is about.
Bobby actually uses these tests on Dean after the latter gets out of Hell, just to make sure Dean is, in fact, Dean. Bobby, being a Crazy-PreparedBadass offers everyone he thinks might be a demon a shot of holy water, or, if he's certain, gives them a beer with holy water in it. He does this test to Sam in Born Under a Bad Sign (he's possessed) and Ellen in All Hell Breaks Loose she's not.
In "End of Days" Dean gets an Eleventh Hour Superpower; given that he's hours from being dragged into Hell, he can now see a demon's Nightmare Face even when they're possessing a human. Lilith cleverly gets around this by possessing demon Ruby, since Dean can't tell the difference between one demonic face and another.
Played for Laughs in "Hammer of the Gods" when Dean walks past an open hotel room containing an elephant...WTF? He walks back for a second look and has an indignant fat black man close the door on him — the fat man turns out to be the Hindu god Ganesh, whose natural form is an elephant.
Star Trek: Deep Space Nine's brand of Changelings, the Founders, are liquid beings that can perfectly mimic any object (though some, like Odo, can't get the faces right). In later years, the only way for the Federation to scope out a Founder is through blood tests, as any material drawn from a changeling reverts back to its own natural liquid state (that looks very different from blood).
The X-Files episode "The Unnatural" is about an alien who falls in love with baseball, taking on the form of a Negro player in 1947 Roswell. At one stage while he's asleep another character sees his true Grey alien face reflected in the window of the bus they're traveling on. The image disappears when he wakes up.
In the Doctor Who episode "The Vampires of Venice", the vampires cannot be seen in mirrors, are burned by the sun, and reveal scary fangs when they attack. Turns out to be literalGlamour Failure, as they are actually a race of non-humanoid Fish People called Saturnynians, using a "perception filter" to look human. However, the combination of actual reflection + perception filter confuses your mind, so it just doesn't see any reflection, the fangs is your subconscious warning your conscious mind of the danger. Their fear of the sun is because the heat quickly dehydrates them, which makes sense since, well, they're fish..
The idea that the Perception Filter shorts out when people are in danger actually can be nicely applied retroactively to Torchwood, which finally gives a good explanation as to why no-one ever fell down the hole left by the base's lift.
A few psychic paper examples; it doesn't work on people who know about it, and the person using it can't let their mind wander, or else the message can change. Also, in season 3 the Doctor tries to use the paper on William Shakespeare and finds out geniuses see it as what it is: a blank piece of paper.
In the Ultraviolet series (not Ultraviolet, but also about vampires) they don't show up in mirrors, camera or film, they can't be heard in audio recordings, and when they captured one they found they were unable to even take a fingerprint from it. This does also cause problems for the vampires themselves, as for instance telephones do not pick up their own voices.
In the True Blood season 4 opener, Sookie finds herself in the Fairy Realm, which looks like a beautiful garden filled with young, attractive people, all of whom are either faries or fairy/human hybrids, like Sookie herself. After Sookie realizes that the "light fruit" is a trap for the hybrids (anyone who has tasted it can never return to the human world), she blasts the fairy queen with her light powers. Suddenly, the garden turns into a desolate landscape, and the fairies reveal their true appearance - that of goblin-like creatures with sharp teeth, pointy ears, and claws. Apparently, the queen was the one who maintained the illusion of a paradise.
Also, in a literal case of Glamour Failure, the vampiric "glamour" ability (akin to hypnosis) is completely ineffective on Sookie (what with her not being fully human and all).
The supernatural beasties called Wesen in Grimm reveal their Game Face when excited or caught off-guard. Even then, ordinary people still perceive the human disguise; only the eponymous line of monster hunters can detect the Glamour Failure. That said, there are times when the Wesen can show their Game Face to normal people if they really try and push it. The major downfall is most tend to Go Mad from the Revelation as their human mind cannot comprehend what they are seeing.
Forever Knight: Animals can sense the evil nature of Nick and the other vampires.
Nick and the other vampires had typical vampire reactions to sunlight, garlic, crosses (though Nick could hold one for a few moments due to a built up tolerance)ect. Nick wasn't supposed to show up in a mirror, but budget limitations led to occasions where it was said his humanity let him show up in the mirror.
Highlander: The buzz that one immortal felt from the presence of another nearby.
Cole in Tracker could sense the life force of another alien if they were close enough. Varied with hybrids, though, Mel was part Cirronian but though Cole seemed to have suspected, he couldn't pick up on her life force. Also could be impared if he was too close to lodestone.
Vampires in Moonlight are burned by silver (in any form, not just silver crosses), and their image cannot be captured on film. The explanation given was that the chemicals used to develop the film included silver, which destroyed the vampire's image. However, they can be seen in mirrors and their image captured with digital cameras.
In Jewish, Russian, and some other folktale traditions, demons and vampires had bird feet which they couldn't conceal no matter what form they took.
There is a story about the Welsh Saint Collen who entered a fairy castle at the behest of its king. He was invited to a banquet there, but wisely refused to eat, remarking that the food was only tree leaves. When the king asked what he thought of the red and blue garments worn by the castle servants, Collen said that the red signified the side being burnt and the blue signified the side being frozen. He then poured holy water on the ground, causing the castle to vanish.
In Swedish folklore, trolls, sorcerers and the Devil can förvända synen — "warp the sight" — in onlookers. While there are some standard folkloric methods of protection, two bear mentioning. First, in many legends it is a active process. If the supernatural being isn't aware of you, you can see their true shape. For instance, there is a common story of a sorcerer who is heckled by a young woman. He threatens her and says he can call the river to raise up, and indeed a flood appears, so the woman jumps on a rock and lift her skirts. Another woman who comes by unseen by the sorcerer, however, see her jumping the rock and showing her unmentionables — there is no flood. Second, some beings with glamour are trapped by their own vanity. Trolls, for instance, usually appear incredibly beautiful and dressed in expensive clothing, looking like refined ladies or gentlemen. Which seems useful, but the natural habitat of trolls is empty wilderness, preferably in the middle of the night, where rich gentlemen and fine young ladies don't wander around willy-nilly.
According to some Arabic folklore, Ghouls can change form except for their telltale hooves.
Gods in Hindu Mythology are said to be distinguishable from humans because they do not blink or sweat, the flowers on their garlands do not wither, and they hover slightly off the ground.
In some versions, mermaids who took human form could always be identified because the hem of their dresses would always be wet, no matter how hot the day was or how long they were in human form.
The Far Side had a man ranting on a soapbox about vampires being everywhere. None of the passersby seem to be listening to him, and the reason why is apparent in a large mirror being carried across a nearby street, which shows a reflection of him alone.
In Changeling: The Lost, the Mask that disguises changelings as mortals always shows some small hint of their true nature and appearance. This gets worse as they become more powerful — the most powerful, although still human in appearance, look decidedly off, and are unlikely to be able to go anywhere without drawing unwanted attention. Also, certain people can sometimes see through the Mask — the insane, those who are high, fetches, very young children, people with certain forms of brain damage... it's not a sure thing, though. Furthermore, a changeling's shadow always shows hints of their true nature — if you were turned into a mountain goat, your shadow's going to show horns, even if you strengthen the Mask to the point that even other Changelings can't see through it, or use Contracts (Fae magic) to appear as something or someone else entirely. Fortunately, the shadow only looks 'off' to other fae or creatures that can see through the Mask, not to everyone in general.
In Promethean: The Created, Prometheans appear human, but other people can sense that there's something wrong about them on a deep, fundamental level. This feeling can build over time until the point where a lynch mob is forming. It gets worse when a Promethean uses their innate powers around another person, because then the glamour fails utterly and they can see the Promethean in their true form - an animated corpse.
Vampires in Vampire: The Requiem typically leave blurry images in mirrors, photos, and films though they can usually make the image look normal by focusing their will. The Hollow Embraces never leave any reflection of after- image at all.
Vampires in Vampire: The Masquerade do not have any problems with cameras barring any supernatural Flaws that do something about it. However the Lasombra either don't leave images on cameras and mirrors, or they have a weird abnormality which means their reflection is that of what they would really look like if they weren't turned into vampires: usually a rotting corpse or a walking skeleton.
Also in Masquerade, the Obfuscate Discipline (which either makes the user invisible or appear to be someone else) is generally ineffective against cameras or other mechanical sensors.
In Hunter: The Vigil, most Conspiracies have equipment or abilities that let their operatives pierce the various illusions and disguises used by the supernaturals, frequently while also indicating werewolves and other shapeshifters in human form as being non-human.
The tiger-like Rakshasa in Dungeons & Dragons are demonic shapeshifters (derived from Indian folklore) who can disguise themselves as any humanoid creature, with the caveat that their hands are always facing the wrong way on their wrists.
This has varied over the years from the hands being upsidedown to the palms being on the wrong side. i.e. the left and right hands were switched. Another version from the spinoff parody Dungeon Hack described their hands as being upsidedown and switched, so that the palms faced inward, but the thumbs were on the bottom and the pinkies on top. This is the only version where the palms faced inward.
D&D also brings us the "Changelings", a sort of doppleganger/human hybrid who can appear like any sort of humanoid they wish. However, a true seeing spell will easily reveal their true form. For the record, they're grey, with gangly and slightly off proportion limbs, white eyes, and only the slightest indication of a nose and mouth. They also turn back if killed.
Infant changelings are also unable to maintain a fake appearance while asleep, returning to their true form. There are also certain size and mass limitations for a changeling's transformation.
An article on Changelings in one Eberron sourcebook dedicated a section to "ways to spot a Changeling". The top causes of Glamour Failure are an incorrect accent, incorrect clothing (the body might transform, but the clothes do not) and a lack of knowledge on local customs.
While vampires of D&D appear mostly as they did in life they are easily distinguishable by their lack of shadows and reflections.
In Exalted, the Lunar Exalted are shapeshifters extraordinaire, but each one possesses a single animal feature — its Tell — that remains consistent regardless of what form it takes. The Tell is usually fairly subtle, such as an oddly-colored patch of hair or strange-looking eyes, but it does allow anyone who knows what he's looking for to identify the Lunar.
Also in Exalted, Solars have a awareness charm that make them ignore glamour as if it were not there.
In the Shadowrun universe, mages have to learn and cast a more difficult (reflected in drain rating) version of illusions if they wish them to fool electronic sensors too. (Cybereyes don't count because they are bought by the owner's essence.)
Nobilis: for the weirder Powers, Afflictions that reveal something about your supernatural status fall under this category. You get Miracle Points whenever, say, your reflection burning like a phoenix or your shadow running off to buy USB drives or whatever it is causes serious problems for you. Also, Lord Entropy's Red Right Hand - his palms constantly dripping with blood - remains constant no matter what form he takes.
The Dark Eldar use strange technology to appear youthful and sexy to the majority of beings, but it doesn't work on psykers and daemons. To them, the Dark Eldar appear in their true forms, as hideous, rotting corpse-like monsters.
In the first Dream Sequence of Lady in the Dark, Liza Elliott dreams of herself as a wealthy, glamorous lady in blue. As in her dream she is a renowned celebrity with legions of admirers, she can hardly refuse to allow her portrait to be painted. When the portrait is unveiled, it shows Liza as the austerely dressed, neurotic magazine editor she really is. Consternation ensues.
In The Legend of Zelda: A Link to the Past, you find a girl trapped in one of the dungeons who asks you to lead her out, but if you do so she tells you not to go out that way. You have to lead the "girl" into a room with bright sunlight coming in, which reveals her to be the boss Blind.
Which makes it very odd that, when you first rescued her from the dungeon, she asked "Please, take me outside."
In Phantasy Star Online, in the Seabed area, there are robot enemies that are usually invisible. However, you can see their reflections in the water and reflective surfaces that are usually common throughout the area, making it possible to attack them. Also, using a lightning spell will short out the invisibility for some time.
Reversed in one of the possible quests in the video/PC game Darkstone. A witch has cursed the women of a local village to turn to stone if they ever become more beautiful than she is. Since she looks to be about three million years old, all the women are statuary. Your character must visit the local dungeon and find a perfectly normal-looking man who is convinced that he's ugly as sin, so has come down to find the Fountain of Youth in order to hopefully fix the problem. Turns out that his real problem is that he's been using something called the Mirror of Lies, which makes beautiful people appear ugly and vice-versa. After getting it from him in exchange for a normal mirror, your character gives the Mirror of Lies to the witch, fooling her into believing that she's young and gorgeous again, so she releases the spell on the village.
In the Kingdom Hearts series, the screen tends to fill with TV static when artificially-made memories start to fail.
In Super Mario RPG: Legend of the Seven Stars, the fake residents of Seaside Town look sort of like real mushroom people, except they have metallic colors and don't move like a normal mushroom person should.
In Paper Mario, the Koopa Bros. attempts to block off the Toad Town gate via apparently magical Toad disguise fails because their hats are black and they pretty much try to be conspicuous.
Paper Mario also had an instance where Peach magically disguised herself as one of Bowser's Mooks in order to sneak around the castle. The reason Kammy Koopa was able to figure out the deception? Peach smelled too nice.
In Devil May Cry, when Dante and Vergil's father Sparda took human form, his shadow remained shaped like a demon.
Bayonetta features a similar example to DMC in that her physical form is always the normal but her cast shadow will display her butterfly wings that she uses to double-jump.
Spies in Team Fortress 2 have both an invisibility watch and a disguise kit. The invisibility will flicker if the spy is shot or if someone runs into them, and the disguise will fail if they use their gun or knife. If an enemy pyro lights a spy on fire, the disguise and cloak are maintained, but they are completely worthless as friendly players cannot be lit on fire, and the player is clearly a spy once they're on fire.
Plus, ya know, the whole "burning to death" thing.
The cloak will actually fizzle out if a Spy gets covered in Jarate (the Sniper drinks way too much coffee) or Mad Milk (whatever is in that jar the Scout's holding, it isn't milk). A disguise won't vanish, but since Jarate and Mad Milk don't affect allies unless they're on fire, and since they'll cry out when they get hit...
In BlazBlue, when Captain Hazama makes his appearance at the end of the game, he becomes so animated and overjoyed about his victory, that he reveals himself to be Yuuki Terumi, an immortal, nigh-unkillable psychopath. Perhaps the only example of a Villain's glamour failing due to sheer enthusiasm.
In Chronophantasma, when Relius uses his Astral Heat on Terumi, Relius has him bound to a chair with a mirror behind him, revealing Terumi's true form.
There's a point in Ōkami where you must encounter a creepy old couple. Pull them into the moonlight and their shadows reveal that they're demons. Though due to their creepy and somewhat disturbing demeanor, it's not that much of a surprise when they reveal themselves. In fact, it makes more sense.
Scotia in Lands of Lore: The Throne of Chaos possesses a magical ring that allows her to take any form she wants. The only thing she can't disguise is her eyes, which are always yellow. On several occasions, she uses this ability to try and trick the player.
The Dungeons & Dragons-based Beat 'em UpTower of Doom has a Displacer Beast as the boss of Fort Cruth. It does the species's traditional projecting-a-false-image... but a guard you meet just before the battle notes, "Why would two beasts only cast one shadow?" Indeed, the real one is the one with the shadow.
The Elder Scrolls V: Skyrim: The more a vampire feeds, the less powerful they are but also the more normal looking they appear. If the player becomes one, going one or two days without feeding and people start noticing odd things like how pale your skin is or your creepy eyes. On day three you suffer catastrophic glamour failure and most NPCs will start shouting "BURN THE VAMPIRE!"
With Dawnguard installed, this penalty is removed and NPCs no longer grab their torches and pitchforks to chase you out of town. However, it's said that everyone is completely terrified of you, for reasons they can't exactly pinpoint.
Dawnguard also redesigns Vampires so they now possess Glowing Eyes. While logically this should immediately give the game away, it's possible that only the Dragonborn can notice this, due to possessing a unique Aedric soul.
Werewolf players also have minor glamour failures according to guard banter, wondering did they just see fur growing out of your ears, ask if you've been tending hounds because you stink of dog, as well as noticing your disturbing wolvish grin.
In Pokémon, Zorua and Zoroark can be sent out disguised as another Pokemon. However, it cannot use moves other than its own, so you can often tell it's a glamor (although it could be a hack as well). Also, it reverts if it takes a hit.
A less obvious tell in that it's a pure Dark Type, meaning it's immune to psychic. Using a psychic move will be ineffective, but most players end up wondering why it didn't work, at least until the next turn. It doesn't even revert. Also, because it's only ever Dark type, if it shows vulnerability to something the Pokemon it is disguised as shouldn't be affected by, such as a Flying type Pokemon to spikes, it gives itself away.
Another situational tell is that the two will only have their own ability, not the ability of the Pokemon they're disguised as. Some Pokemon have abilities that immediately alert the opponent or take effect immediately when sent. The lack of this event reveals the Pokemon as Zorua or Zoruark.
Surprisingly an Inverted Trope in The Legend of Zelda: The Wind Waker. On a New Game+, Link's Grandmother, instead of giving him the iconic green hero's clothes, gives him what's either invisible clothes, or absolutely nothing. Link wears them over his normal clothes, with absolutely no difference. It seems at first that she's just playing a joke on him, but looking at Link's shadow reveals the indistinctive shape of his floppy hat. This may also be a programming oversight, however. According to his grandma, they're magical clothes that are only visible to honest people. "What's the matter? You see them, don't you?"
The protagonist of Fox Tails, Keen Kotaru, possesses a so-far unexplained ability to see through the Glamours of the various animal-spirits that are otherwise maintaining a Masquerade in our world. His ability to thus notice the remaining animal features of transformed spirits is what drives the plot, and allows him to effectively fight the evil spirits...
In Errant Story, the Elven Rangers who move around the world of men in search of 'Errants' (half-elves who frequently become psychotic) often uses glamours to disguise their elven nature. At one point, however, a young child can see through it, though her mother dismisses it...
In Dan and Mab's Furry Adventures , the Cubi all possess powerful shape-shifting abilities, which obviously comes in handy for many things. However, they all have a single "marking" on them that they cannot change — and which also shows what clan they belong to. If you manage to spot such a mark, and happen to know what they mean, you'll both know that you're actually facing a Cubi — and usually whether it's the kind that feasts on pain, terror and suffering, or the kind that feeds on lust, joy and happiness. Very handy for determining what your next response should be, really. Although make-up or clothing can conceal them, but only real clothing, not clothing made by shapeshifting.
In Gunnerkrigg Court, certain individuals are living Glamour Failure, who unconsciously dispel illusions by their very presence. Antimony is one such person, as her encounter with the ghost in the hospital showed.
Ironically, this can work against her. During the trip to the afterlife bureaucracy, Kat has such a logical perspective that everything she sees looks like a Halloween house, while Antimony and Mort can see the afterlife in all its magnificent glory. Regardless of who has the 'real' perspective, Kat's perspective allows her to flip off an old man in a horror costume, while Antimony and Mort see said old man as a GIANT PERSONIFICATION OF RAINBOW SKELETAL CENTIPEDE DEATH. He even leaves his room because Kat ordered him to!
Last Res0rt uses the "Dead Eyes" of the Djinn-si as a quick tell-tale for identifying most Dead Inside, and it's also the only part of Alice's body that can't be changed by shapeshifting.
In Tales of the Questor, the illusions of the Fae can be pierced by someone born with "the second Sight..." or by someone with the latent ability who daubs their eyes with elderflower balm or drinks elderberry wine.
The webnovel John Dies at the End tells the story of two college dropouts who discover and fight an otherworldly invasion after a chance run-in with a supernatural drug changes their perceptions forever. As a result, they see a lot of freaky stuff invisible to everyone else, but they also gain a lot of experience identifying subtle clues that ordinary people could notice if they paid attention. They learn mirrors can be used to circumvent certain illusions, religious symbols can be used to flush out and ward off evil, and household pets can be used to detect and identify paranormal beings.
The French supervillain Mindscape, from the Global Guardians PBEM Universe, avoids cameras as often as he can, because anyone viewing him on film or in photographs can instantly tell he's a deformed hunchback and not the GQ-quality supermodel-handsome man he uses his powers of illusion to pretend to be.
At the very end of the pilot of Bee and Puppycat Puppycat's reflection in a window briefly changes to show the outlaw in a story Puppycat told earlier.
Hilariously done on the children's show Count Duckula, where the eponymous duck decides to redecorate the castle and one decorator hired does the place up in all windows. Since the duck is a vampire, he can't see himself in any of them.
Batman Beyond: Whenever Derek Powers got angry, which was frequently, his powers would flare up and start to burn through his artificial skin, revealing that of the radioactive, glowing villain Blight. Actively using his powers for even a few seconds will completely shatter it, requiring him to have new skin grafted on. His inability to keep his skin on through the events of any given workday actually makes him a case of Blessed with Suck. This worsens as he undergoes a figurative meltdown, followed by a literal meltdown which left him dead for good.
In Samurai Jack, anything Aku transforms into has the same black/green/red color scheme he does, and his true form shows up in reflections. He managed to disguise himself as a beautiful woman and fooled Jack in one episode, after which Jack stayed alert; a second attempt at masquerade led to Aku being totally outmaneuvered.
While not a person, an episode of Justice League Unlimited has Hawkgirl discover a mine on a faraway planet was fake (and, thus, a trap) when the holographic shadows it cast from her glowing mace didn't follow the same direction of the other shadows the mace cast.
Earlier, a spell cast on Superman and Wonder Woman to make each think that the other was a demon could only be broken once they saw the other's reflection. The problem was that, once Superman saw what was going on, he felt unable to fight Wonder Woman, and thus had to take a beating until Wonder Woman saw it too.
And there is the whole "In Blackest Night" episode, where John is tried for destroying a planet. The others notice the planet's sattelite is still orbiting it, find the holoprojector, and blast it apart, causing the planet to reappear right in front of the judges.
Kurt's image inducer. Given that it really only needs the settings "off" and "on" was there really the need to give it so many options and make the off button so incredibly easy to press by accident? As the image inducer only makes him LOOK human, anyone who touches him can still feel his fur. In the comics, he uses it at least once to trick a villain. It could've been a set-up for future writers that just never got used.
Quicksilver has his moments too. It's implied that being super-fast is his natural state and that it takes an effort to slow down to human pace, and, as such, he speaks slightly faster than any other character and often can't restrain his powers over small distances; for example, in his first appearance, when he zooms around Evan in the locker room before revealing himself more dramatically later on.
The Simpsons episode "Bart Sells His Soul" features a number of these: automatic doors don't open for soulless Bart, he can't fog up glass with his breath, he can't laugh, his eyes briefly turn cat-like as he performs a Hiss Before Fleeing, etc.
Beast Boy retains his green color when changing into other animals. This would make infiltration difficult.
Beast Boy: Do I hear an undercover mission coming on, 'cause I'm a master of disguise!
Raven: Yeah, a green mongoose is gonna blend right in.
The Christmas special "The Story of the Leprechaun's Gold" had a situation where banshees could take human form, but were always identifiable by their banshee tears, which they could not hide.