In Magical Girl Lyrical Nanoha StrikerS, one of the characters, Subaru Nakajima, walks out of an explosion, covered in blood and one arm missing a large chunk of flesh, revealing the cybernetics underneath, during her scene of Unstoppable Rage. Interestingly, there's no Artificial Human-related angsting here, partly because most of the Nanoha cast aren't human, and have no problems at all accepting it.
And unlike Fate and Erio, Subaru and Ginga had a loving family, and complete knowledge of their origins long before the series even began.
Hell, by this point in the series, the Bureau probably has "So you're not exactly what's traditionally considered human, that's okay because you're a person too and we support you" pamphlets. (Probably written by Fate and Nanoha.)
Happens again in the PSP games, The Florian Sisters are full androids.
Happens in Armitage III Dual Matrix with the titular character, made worse by the fact that it's her kid that sees it and becomes immediately afraid afterwards.
Happens to Armitage and D'Anclaude, among others, in the original series; Ross Sylibus' Artificial Limbs are revealed this way, as well.
Bartholemew Kuma of One Piece was revealed as a cyborg this way.
The MIB chasing after the Crescendolls in Interstella 5555 are revealed to be robots when, after an explosion, parts of their skin burn off and reveal metal.
In Bubblegum Crisis 2033, Largo's boomer status - which had been implied before - is confirmed when Leon shoots him in the hand, leaving a small hole with sparking metal visible inside.
The first episode has this happen to the kidnapped little girl, who is as surprised as anyone else that she's a Boomer with the Phlebotinum to control the military's Kill Sats.
A variation occurs in Kara no Kyoukai when Shiki's arm gets possessed, and we see the skin covering melt off to reveal that it's really a puppet arm. The rest of Shiki is human, but the arm is artificial.
Major Montana Max in Hellsing after being shot by Seras.
After being on the receiving end of a reflected fire spell, Mubyou in Wagaya No Oinari Sama is revealed to be a robotic duplicate of the real Mubyou. Since the real Mubyou is always Walking the Earth, she created a few puppet copies of herself to work in the lands she's not currently in. Seems the duplicate Mubyou just wanted to be acknowledged for her work.
At the end of one episode of Yu-Gi-Oh! 5Ds, a flying spinning spike of doom flies towards Rex Godwin. He catches it with his hand seeming to suffer no ill effects to the total shock of everyone watching... turns out his arm is robot. Coupled with the fact he possessed a severed arm in a test tube with a Dragon's Birthmark on it, this led some people to suspect that he may have been the 5th Signer. However, it turned out he wasn't the only one missing an arm...
Ghost is revealed to be a robot after it loses to Yusei and crashes. When the lads go to help it, Crow touches it's shoulder, and it's arm falls off.
Placido, both when he combines with his D-Wheel, and later when he is blown apart at the waist.
Inverted in the Third season of the original Yu-Gi-Oh!. The gang meets up with a robot monkey, but don't realize that it's Honda until later
This occurred in Negima!? Neo during the re-telling of the battle between Negi and Asuna against Evangeline and Chachamaru. Chachamaru uses herself as a shield to save a group of cats which had gotten caught in the fray, causing her shoulder and upper thigh to spark and a metallic skeleton to show beneath her skin. In the regular manga, she simply showed them her Jet Pack by accident.
I'm pretty sure that in the manga, it wasn't even an accident. She never makes any indication that she's attempting to hide her robotic nature; she even has incredibly obvious antenna ears and pulls out the jetpack in a public place to get a kid's balloon out of a tree. Everyone else (except Chisame) is just oblivious.
Parodied, like everything else, in Excel♥Saga. Ropponmatsu II gets shot in the head, and the circuitry underneath reveals she's a robot. Excel is honestly surprised by this, despite obvious signs of it earlier in the episode. Ropponmatsu herself considers it obvious, and asks how many people shoot missiles from their knees.
Well, considering how stupid Excel is, it's no surprise she hasn't caught on.
In Fullmetal Alchemist, Ed has an automail reveal when his right arm gets attacked by Cornello's pet chimera. In Brotherhood, the reveal is done by a rogue alchemist trying to freeze his blood in that arm.
Izumi also finds out that Al is just an empty suit of armor by throwing him, and concludes that Ed has an automail leg by the fact that his steps sounded different when they were sparring. She's just that good.
The Trinity Blood novels drop several hints about Father Tres Iqus not being human, however it is only officially revealed when he is shot through the arm and his circuits are revealed.
In the final episode of The Big O it turns out that Big Ear, the mysterious informant who's always reading a newspaper when he's spoken to, is an android.
Used to chilling effect at the end of a scene in Ghost in the Shell 2: Innocence; after Batou and Togusa finish a conversation with a forensics scientist about the nature of the Uncanny Valley, her face flips open to reveal mechanical insides.
If you look carefully, you can deduce her cyborg status by noting that she wears short sleeves in extreme cold, and her breath isn't visible even though Togusa's is.
In Gall Force, the crew find out about an advanced android when Pony forces the information out of the OX-11, to be confirmed moments later, when Catty makes a Heroic Sacrifice, and her clothes are burned away to reveal the android beneath.
In Osamu Tezuka's Metropolis, Ken'ichi is the very last person to find out or even consider that Tima was a robot. She was introduced as this at the beginning of the film.
In Gundam 00half of Lichty's body is revealed to be cybernetic when he saves Christina's life at the cost of his own. Since it adds very little to his character, this was most likely due to the fact that it would have looked really gruesome if a normal human body had been exposed to GN particle beam like that, and wouldn't have passed the censors.
AKB0048's Mayu Watanabe looks like just another member of the pop idol group...until she raises her arm and a missile launcher complete with aiming visor swings up out of it. This is not really focused on in the show, though.
In the Votoms OVA The Last Red Shoulder, one of Chirico's old friend, Byman was seemingly untouched by their former treacherous commander Pailsen (Their leader Gregor was wounded and scarred during a failed hit attempt, while other member Muza had his entire family slaughtered while he wasn't home, and Chirico himself was set up to be marked a traitor), until Chirico (who noticed Byman refused to punch Muza with his right hand when a fight broke out) tossed a lit piece of firewood at him, burning off his sleeve and revealing a robotic arm, as Pailsen had tortured and cut off his entire right arm. They promptly stop mistrusting him after that(Muza believed he had no business being with their group when his life was seemingly fine)
The comic's cover showed the new X-Men (Storm, Wolverine, Nightcrawler, Colossus, and Banshee) fighting the original X-Men (Jean Grey, Cyclops, Angel, Beast, and Iceman). The fight actually happened in the issue, with the new X-Men unwilling to fight all-out against their friends. But Wolverine realized that the original X-Men were robots because they didn't smell right. The robots were reduced to scrap metal pretty quickly after that.
X-men enemy Arcade makes robots convincing enough that his appearances in comics usually end up being robots. He was so good at this that when he made a double of Nightcrawler, Mystique mistook it for her son and couldn't bring herself to kill it.(Had no problem vaporizing her daughter Rogue though)
Anna, from the Gen 13 series. She's a demure maid who cooks and cleans for the group, looking very much annoyed when her carefully cooked breakfast goes ignored in favor of various snacks, junk food and cold pizza. Then she turned out to be an assassin droid with concealable blades and weapons of destruction.
Adam Aaronson, Machine Teen, initially believes himself to be an Ordinary High-School Student. His robotic nature is revealed when he gets damaged playing football, but he himself is programmed to think of it as a normal injury.
This was a What Could Have Been in Sonic the Hedgehog. Sometime after the Endgame arc, the original plan was that Sally had been Dead All Along since that arc, and the Sally that's been in the comic since then was in fact a robotic clone who became self aware and ultimately rebelled against Eggman. However, this was given Executive Veto, so Sally ultimately survived Endgame and the clone never appears.
Happened a lot in the Silver Age with Superman who had robotic duplicates that could impersonate him as Clark or Superman. But in an early Post-Crisis story, the first Superman is so perfectly programmed with Superman's personality that he believes he's Superman even after his robot parts become exposed. He genuinely believed he was somehow the real Superman turned into a robot.
In the final panel of the EC Comics story "Strictly Business," the husband shows how easily he could enter into a deliberately Sexless Marriage and tolerate it for three years by opening up his chest...
Inverted in The Black Hole when the Cygnus' compliment of robotic crew members are actually revealed to be the lobotomised remains of the human crew. With Maximilian's help Dr. Reinhardt converted them into subservient cyborgs after they tried to mutiny.
The T-800 cuts the skin off his arm deliberately to prove to the Dysons that he isn't human.
At first, the T-1000 seems like it's the soldier the resistance sent back to protect John, until the Terminator shot him multiple times and he reformed afterwards.
Terminator Salvation pretty much does this in the trailer. While we do not see the entire scene, the gist of the scene explains everything: Medic, trying to patch up a wounded soldier, is horrified when she sees Terminator circuitry, calls over John Connor, who ties him up and interrogates him, before untying him when he sincerely doesn't understand why the hell he's tied up, just so he can see it for himself. Cue the horror.
Beta in The Last Starfighter, when he was wounded in front of Alex Rogan's girlfriend. Moments before, Beta had been trying to convince her that he was a robot. She didn't believe him. He gets shot, shows her his circuits, and says, "See?" before chasing after the attacker.
In the 2004 version of The Stepford Wivesit's revealed when the main character knocks his head off that Mike Wellington is actually a robot, while it's his wife that's the programmer, an inversion from the original movie.
Both film versions have the scene where Joanna confronts the mysteriously changed Bobbie and goes so far as to stab her. The Stepfordized Bobbie acts very strangely for someone with a kitchen knife in her stomach. Maybe Joanna should've done anything now, but the plot seemingly required her to be an idiot.
Which makes the 2004 version even more stupid when you find out all the Stepford Wives are human women with microchips. Because microchips make a gut wound all better.
The 1975 version features a chilling climax when Joanna meets her robot double.
Alien: Ash, the ship's medical officer. By bashing his head off.
Aliens: Bishop, thanks to the infamous knife-trick.
Alien³: Inverted when someone suspected of being an android is violently attacked, only to start bleeding very human red.
Alien: Resurrection: Annalee Call. During their escape in the elevator shaft, Wren has trouble opening the shaft door. He asks for Call's gun which she readily provides, not realizing her mistake until Wren shoots her in the chest, knocking her off the ladder and into the water with a very determined xeno on the group's tail. After they take out the xeno, they are suprised when Call opens the shaft door from the other side, soaked with water. Though she doesn't want to talk about what happened, Ripley saw her being hit and her light clothing betray the fact that she doesn't have body armor. She opens her jacket and reveals circuits and synthetic liquid instead of bone fragments and blood. Androids built by Androids are illegal so Call hid her own identity to stay alive. Needless to say, the rest of the team (except Ripley) didn't like this one bit until she proved her worth by crashing the Auriga.
In Starchaser: The Legend Of Orin, the villainous Zygon turns out to be a robot when Orin cuts his cheek. Although that really shouldn't have been a surprise to him, since the dude was running a robot empire and was strong enough to pick him up and choke him with one hand.
In Bill and Ted's Bogus Journey, done three times by the "evil" Bill and Ted robot usses. The reveals lean toward terrifying, but the second time, when human Bill punches his twin, is probably the funniest. "Oww! You're metal, dude!"
The German silent film Metropolis had one of the first robotic reveals. A Mad Scientist creates a female robot that is identical to Maria, a woman who preaches about peace to the enslaved workers in the city who want to revolt. The real Maria is kept away as the robot inspires lust among men and violence among the workers. When the city falls to pieces, and the people decide that Maria is to blame, they tie her up to a stake and attempt to burn her to death. She laughs as her 'exterior' melts away, revealing that she is a robot.
In a 2004 Disney ChannelMade-for-TV Movie called Pixel Perfect, a hologram named Loretta is created by a teenager to help his best friend's band. Loretta is thought to be human until the band's second performance, when she starts fading in and out. But, in a slight subversion, everyone loves the holographic lead singer.
In Surrogates, The Prophet is revealed to be a Surrogate controlled by the Surrogates' inventor.
The President's Analyst - near movie's end, the good guys have stormed the headquarters of The Phone Company. Finding themselves facing the company's blandly cheerful president, they're surprised to find he's an animatronic figure.
Masters: He's a recording!
Kropotkin: It's like a visit with Abe Lincoln at Disneyland!
Screamers: Happens to the humanoid Screamers. Exaggerated Trope; there are so many new generations that the protagonist eventually has trouble believing that anyone besides him is even human. In fact, he visits the enemy camp (dwindled down to three remaining soldiers) and the soldier who is killed under suspicion of being a Screamer turns out to be the only one who wasn't a robot.
In E. T. A. Hoffmann's 1816 short story, "The Sandman", the main character falls in love with a woman named Olimpia, who is eventually revealed to be a robot.
Elijah Baley is told from the start that R. Daneel Olivaw is a robot. He refuses to believe it, however, as robots that advanced don't exist on Earth in his time — and he has a brilliant theory about the murder of the human in whose image Daneel was built. When Daneel peels the synthetic flesh off his arm to prove himself, Baley faints (for several reasons).
And then Elijah pulls off his trick in the sequel.
Though Hari Seldon doesn't find out that Dors Venabili is a robot until long after they met.
Animorphs did this a little differently. They morph dogs, and just-so-happen to run into an old acquaintance of Marco's as he's passing out fliers for the Yeerks' front organization, and they freak out because... Erek has no scent. Because this might be a new weapon of the Yeerks, they stalk him until he just-so-happens to get hit by a truck and his hologram shorts out for a split-second. It's not until they morph spiders (which see a different wavelength of light) that they can confirm that he's an androidnote Or maybe more of a cynoid in disguise?, however. Erek turns into a fairly important minor character, as the Animorphs' spy inside the Yeerk organization and using his and his friends' holographic abilities to impersonate the Animorphs so that they can go into outer space or something without being missed.
In "The Eleventh Voyage" of Ijon Tichy, the main character of The Star Diaries by Stanislaw Lem, this gets totally inverted. Tichy, sent in a robot disguise to a planet inhabited solely by machines that are hostile to all humanity, discovers in the story's finale that there is no single robot around the place. All of the alleged machines are in fact secret agents like himself, who have been exposed one by one, and forced to keep up appearances. Furthermore: the computer mastermind behind this plot shows up to be merely a humble human gofer working for the agency responsible for sending all those people on a mission to that planet. The story is a parable of living in a country, where everybody upholds the official ideology no one actually believes in, which was the case of People's Republic of Poland at the time when Lem wrote the thing.
In Fritz Leiber's Silver Eggheads, this trope is ridiculed by a robot writer Zane Gort, who writes books for robots (and is not averse to use an Un-Robotic Reveal himself):
Zane Gort: You know, it's funny how humans are forever ending stories or episodes with the discovery that the beautiful woman is a robot. Just at the point where it starts to get interesting. And ending it bang without one word of description as to the robot's shape, color, decor, pincher-style and so on, or even telling you whether it's a robot or a robixnote i.e., a female robot.
Live Action TV
Red Dwarf. in "Out of Time", Lister gets his arm cut, revealing mechanical parts. Not only mechanical, but of a model inferior to Kryten, which means Kryten technically outranks him! The whole thing is then beautifully subverted when it turns out that Lister's mechanical "nature" is the result of Starbug having hit an "unreality pocket", turning Kryten briefly into a gibbering idiot as he attempts to apologize for his mis-step.
Power Rangers Operation Overdrive: Red Ranger Mack is revealed to be a robot built by his "father" after a computer virus that infects the Rangers' base afflicts him as well, and he's forced to be taken off-line and disassembled to get at the problem. Needless to say, he wasn't very happy about it.
About ten years prior, Power Rangers Turbo had an episode where the Blue Ranger Justin suspects that the other four Rangers have been replaced by robots. As it turns out, he's right. The real sting? Justin HIMSELF is revealed to be a robot like them, when the real Justin shows up to deactivate him.
In Power Rangers S.P.D., new cadet Sophie is discovered to be a robot when the Rangers walk in on her repairing the circuitry in her arm.
Power Rangers RPMinverts this. Tenaya 7 is convinced she is a machine, until a cut in a fight reveals she bleeds. The camera angles play with this trope, mimicking its straight use and treating the blood as if it was the tell-tale sparking wires. In fact, the straight usage had happened earlier in the same episode to a part of her body that was mechanical, though it was likely to emphasize that she did have robot parts. There's also the finale, where it's revealed that around half of the citizens in Corinth are sleeper agent cyborgs, and Venjix is just about to activate them.
The Buffy episode "Ted" has Ted revealed as a robot after Buffy clobbers him.
We know that the Buffybot is a robot, but it's revealed to a vampire after he injures her, revealing electronic parts (and causing her to bang into walls).
Likewise when Glory knocks the Buffybot's head off.
Glory: "The Slayer's a robot? Did everybody else know the Slayer was a robot?"
Unnecessary for April in "I Was Made to Love You". Her behavior makes it perfectly clear to everyone that she's a robot. Which makes it Everybody Knew Already when her creator Warren tells Buffy something she "couldn't possibly know".
In the Angel episode "Lineage", after Wesley kills his father, the latter is revealed as a robotic replica.
In Andromeda, Doyle is revealed to be an android when she cuts her hand and bleeds superconductor fluid. As a small twist, it's revealed to us, but not to her, since Harper programmed her with a perception filter that causes her to think it's blood.
In "Victory Of The Daleks", Professor Edwin Bracewell's hand gets shot off by a Dalek, revealing him to be a robotic creation of theirs, so that in turn the Daleks have proof that Bracewell 'created' them. They also made himas an explosive device.
The reimagined Battlestar Galactica finds plenty of ways to reveal that characters are not quite human:
As artificial humans in this world are mass-produced, a favourite is simply to reveal that (an)other identical version(s) of a character exist(s). This is done with Boomer, Sharon, D'Anna, Cavil and Gina (in the movie).
In the first Season we also get the fact that their spines glow when "getting intimate". This was dropped in later Seasons (probably because it's pretty stupid and provides a simple "Cylon detector" for humanity).
Caprica Six simply tells Baltar she's an android; as she knows the world is about to be invaded by her fellow killer robots this is not much of a gamble.
Leoben Conoy behaves oddly, is unusually strong and proves vulnerable to exotic radiation.
A marooned Aaron Doral is rescued by his fellow androids.
Simon is seen talking with another, known, android.
Anders, Tyrol, Tory and Tigh are drawn together and mysteriously 'activated' when the Fleet reaches the Ionian Nebula.
Ellen is glimpsed by another android in a vision.
Subverted with Starbuck. There are many hints that she might be an android but the main thing that suggests this e.g. her resurrection is apparently not due to "downloading".
In an episode of Bionic Woman, after Jaime rescues a girl from some would-be kidnappers, the girl discovers the exposed wiring of Jaime's arm.
In the original series, Jaime herself is horrified when she first tangles with the Fembots; she thinks they're just crazy doppelgangers until she rips one of their faces off during the fray, revealing circuitry and freaky lidless eyeballs. (Her later, delirious warning to Rudy about robots, after they've kicked her ass, is chalked up to bionic rejection. Until Oscar's face suddenly comes off.)
In Farscape Aeryn is kidnapped and replaced with a bioloid copy- which is unveiled when Crichton gets wise and shoots her in the head, revealing pulsating organic machinery beneath the ruined face.
Sikozu reveals herself to be a bioloid as well by rotating her left eye 120 degrees as a signal to another bioloid.
Cameron has a more subtle way of revealing herself, simply by lighting up the irises of her eyes. In this case, though, she is talking with someone who already knows Terminators exist.
In a Sliders episode, the lead researcher for developing Mechanical Life Forms wanted to test out a way to transfer a human brain into a robot. He discovered that the procedure was already performed on himself when he was hit by a weapon.
1960's Batman episode "The Joker's Last Laugh". Batman realizes there's something strange about a bank teller. He twists the man's nose and the top of his head blows off, revealing springs and other mechanical parts. The teller was actually one of the Joker's android robots.
There is an old viral video from the early 2000's by a raper named Pete Miser called Scent of a Robot, which essentially this trope in song form.
There are rules governing this reveal vis-à-vis Cyborgs in Deadlands: Hell on Earth and Lost Colony, particularly if the deadbot in question is equipped with the "Infiltrator" package, which makes a normally pallid cadaver-with-metal-in-its-guts capable of breathing normally, bleeding, eating, and other things. When a cyborg takes enough damage, nearby characters can make a check to see if they notice anything unusual in the wound, with the roll being easier if...
...Your can is continuing to fight after taking enough damage to drop a bull rhino.
Encouraged for Game Masters in the PDQ-system superhero game Truth and Justice. Where heroes get Hero Points to trade for bonuses and to pull off impossible stunts, villains get Villain Points which grant similar bonuses and also allow them to "actually" turn out to have been a robotic double all along, and other forms of instant escape/backup plan. Villains have to be worn down in a series of confrontations to be put away for real.
One of the characters in the first Wild ARMs game is revealed to be not quite what they seem after he cuts off his arm to get away from the Big Bad. When the others treat the injury, sparks fly out, and they discover that his insides were made of the same properties as the Metal Demons.
A variant occurs in Super Smash Bros. Brawl when The Ancient Minister, who up until this point was considered to be a variant of one of the Big Bad's Mooks, turns out to be a THE R.O.B.
In Tomb Raider: Chronicles, in the final level you encounter suited henchmen who seem extremely tough, after causing enough damage it is revealed that they are Cyborgs and must be killed by alternative means to shooting.
Dr. Wily at the next-to-last level of Mega Man 3. Although it's kind of easy to tell because they play the regular level-ending song. It did surprise some people because this was only the first game where the bad guy was "Not-Wily".
Done with a twist in Command & Conquer 3: Kane's Wrath, where it is revealed that the player is a Nod AI named LEGION. Presumably, LEGION was aware of its nature the whole time, but the player doesn't until Kane makes the revelation himself.
In Baten Kaitos Origins, the one with robotic innards is Milliarde.
In Streets of Rage 3's Stage 5, you fight Mr. X. Why are you only on the fifth stage when you fight him? Well, upon defeating his henchmen, the top half of him burns off to reveal a robotic duplicate. The real Mr. X, who you encounter in Stage 7 (assuming you rescued the General Chief of Police), has been reduced to a brain.
Played straight with the final boss of the first Turok game. The Campaigner at first appears to be some sort of barbarian wizard, but as he takes damage his flesh peels off to expose his robotic structure. In some ways there is a subversion of this trope, as the player has already cut down legions of "real" humans by this point.
Cave Story: Professor Booster apparently recognizes the protagonist as a robot immediately, but several other characters—particularly Kazuma, and possibly the player—don't realize this until Booster points it out. In their defense, he is a Ridiculously Human Robot.
With white skin, inhuman eyes, and antennae for ears.
Somewhat played with in Metal Gear Solid 4, right before the final boss fight with him, Ocelot dramatically removes his jacket to reveal that Liquid's arm has been replaced with a bio-mechanical prosthetic, hinting that "Liquid" was artificial.
In Snake's Revenge, Big Boss reveals before the final battle that he was turned into a cyborg. After he sustains enough damage, he transforms into a tall cyborg who chases after Snake across several rooms.
Inverted in Metal Gear 2. In an optional radio call during the final battle, Kasler tells Snake that Big Boss underwent an operation to replace his limbs with cybernetic organs. When Snake defeats Big Boss with a makeshift flamethrower, he burns to death like any other person (he did get better).
In the first Sonic Advance, halfway through the fight with Metal Knuckles, his outer covering breaks off to reveal his metallic body. (Of course the fact that he was a robot was All There in the Manual, but only in the Japanese version.)
Conkers Bad Fur Day, being the Shout-Out-heavy game it is, throws one out to Terminator with the Haybot, who looks like your average musclebound anthropomorphic stack of hay until you stick Frankie's forks in his ass twice, at which point part of him burns away to reveal the ever-familiar image of a robotic red eye. "BUFF YOU, ASSHOLE!"
A minor reveal in Mass Effect 3: after chasing down a Cerberus agent on Mars, Vega rams her with a shuttle. Cue her emerging Out of the Inferno... her clothes and skin burned off the robotic frame by the explosion.
In Persona 4 Arena, when Labrys'Shadow reveals itself, it forcibly removes Labrys' human guise to reveal to everyone that she is actually a robot.
In Echo Night Beyondthe young man is revealed to be a robotic copy of Kenneth, a man who was killed. Also, Richard, the player character is a robotic copy of the real Richard (aka. the space station chief) made by his ficanee (who was in love with the real Richard when he died).
A quest in Rivet City, in the Capital Wasteland, has you looking for an escaped android with fake memories and a new face. As it turns out, the android is the very first person you meet in the city, Chief Harkness.
Subverted in Bionic Heart. When Luke first meets Tanya, she has had half her face blown off by the police pursuing her, revealing the mechanical parts underneath her skin.
In Virtue's Last Reward, it is at one point hinted that there may be a secret robot among the cast. It is eventually revealed that Luna is, in fact, a GAULEM.
This trope also happens in one of the paths when Sigma's arm is cut and a white fluid comes out of it. By the ending of the path, it is revealed that he has cybernetic arms, but the rest of him is human .
Inverted intheseSluggy Freelance strips where Oasis bleeds after being stabbed through the gut, revealing that she's not a robot like everyone thought. Whether she's human in the strictest sense of the word is still unknown, however.
In Morenatsu, one non-canon bad ending on Tatsuki's route reveals him to be a robot created by Shigure. He kills both Tatsuki and Hiroyuki, the latter because he now knows this secret.
In Red vs. Blue, if Carolina didn't figure out Tex was a robot when she was shot in the shoulder—complete with sparks—in season 9, she certainly had to have figured it out when Tex gets stabbed deeply in the back with no side effects in season 10.
Worm has Dragon, a Canadian woman widely lauded as the greatest Tinker in the world, who deploys to each battle with a new set of high-tech battle armor. Her interlude reveals that she's actually a partially developed Artificial Intelligence, severely crippled by the death of her creator while she was still in development.
Oliver, in the Kim Possible episode "Grudge Match", is first pinned to a giant magnet, then has his face pulled off. He was being used as a beard by a supermodel-lookalike robotics expert.
Eric in TheMovie, was acting as a human until he electrocuted Kim while she hugged him, though to be fair, this is more "sack of goo" than "robotic".
Sari Sumdac from Transformers Animated, ends up with a chunk of her elbow missing, with Cybertronian circuitry poking out. This one was just as much a surprise to her as everyone else, except her "father".
Turtles Forever, the crossover between the first two TMNT cartoons, has a reveal when the 2003 Turtles learn the 1987 Foot Soldiers are robots.
2003 Leonardo: Robots?
2003 Michelangelo:(enthusiastic)Exploding robots.
Inverted in South Park, in which Cartman's robot disguise (consisting of a couple of cardboard boxes) manages to fool everybody until he gives the game away by farting.
Also played straight in the "Trapper Keeper" episode.
Every slain enemy in Samurai Jack turns out to be a robot, regardless of how human they looked or behaved, if they were encountered in a cockfighting ring, or even if they appeared to be wild animals. Similarly, any limbs he chops off non-robotic characters will turn out to be cybernetic prostheses.
An episode of Inch High Private Eye featured a mad dollmaker as the Villain of the Week, who uses robot mannequins to rob department stores. When he's eventually caught, the heroes discover they only captured a decoy. He returns for a second run, with mechanical copies of the titular character and his boss, but this time, they catch him for real.
As a matter of fact Hanna-Barbera loves this trope for some odd reason, taking it so far, that sometimes, the main villain of the episode turns out to be one. Nobody seems to question where the robot came from or who built it.
Played for Laughs with a robotic duplicate of Leela in the first episode of the Futurama revival. Everybody except her realized that she was a robotic duplicate, until Nibbler bit a chunk off of her arm, revealing circuitry. She spent the rest of the day screaming. Also done with a Fry duplicate later that episode.
Also spoofed and then immediately inverted in the earlier episode "Insane in the Mainframe", where the trauma of being committed to a robot asylum eventually causes Fry to believe he is a robot. In the episode's conclusion, bank-robbing robot Roberto stabs Fry, but the knife hits a can of oil he put in his jacket pocket earlier, causing Roberto to believe Fry really is a robot. Moments later, Fry snaps out of it when he sees the blood coming from a cut on his arm.
Yet another Futurama episode has Bender going on a fox hunt, only to be hit by sudden empathy when it's revealed the fox was in fact a robot. As were the hounds. And the horses. And, at the end of the episode, the head hunter.
In the Gargoyles episode "Leader of The Pack", Xanatos breaks The Pack out of jail. During an epic fight on board an oil tanker, Bronx tears off half of his face, revealing that "Xanatos" is actually the robotic duplicate, Coyote. Of course, the whole point of the exercise was to get Xanatos' girlfriend Fox a shot at early parole for her actions during the jailbreak at the start of the episode.
In Sealab 2021 Quinn reveals in an episode that he is a robot. This isn't mentioned again afterwards and was thought to just be a wacky joke since there's Negative Continuity. But then a later episode mentioned it again. I guess they don't really seem to care much.
The Teen Titans episode "Masks" first introduces Slade's trademark mooks, who dress decidedly like ninjas. At the end of the first fight with them, though, Robin rips the mask off one of them, revealing the robotic circuitry beneath. Later episodes also had "Slade" being revealed as one of his android doubles, with the real Slade speaking through them from an unknown location. Averted with other Mecha-Mooks later in the series—the robot soldiers that served Brother Blood and the Brain were clearly shown to be machines from their first appearances.
In Young Justice Professor T.O. Morrow is revealed to be a robot when Red Volcano kills him. The real Morrow is dying in hospital, having built a robot duplicate to carry on his work. It subverts Comic Book Time in the process, as Morrow had been active since World War II without seeming to age.