Inversion of the Robotic Reveal, where a machine that was assumed to be a robot turns out to hold a Man in the Machine or some other living creature powering or controlling it. A Mobile-Suit Human may allow this trope to be preceded by a Robotic Reveal as a Red Herring as there's a lot of machinery to expose before the actual pilot is revealed.
Be careful; some of the examples below are inherent spoilers.
Trigun: in the anime Gray the Ninelives (one of the Gung-Ho Guns) was a robot, but in the original manga it was indeed powered by nine dwarfish creatures inside it.
Also, the Plants, which seem to be giant power generators shaped like lightbulbs but are actually humanoid aliens inside giant containers.
Variant in UFO Robo Grendizer -one of the Mazinger Z series- when it is revealed that the Robeastsare powered by brains of Fleedian people. When Duke Fleed got told all Saucer Beasts he had been destroying contained all what was left of his family and friends, he got a Heroic BSOD.
Happens in Eureka Seven as well, when the core of the Nirvash (and therefore all other LFOs) are revealed to be organic lifeforms.
This is the twist in one of the DOLLS manga stories. A woman abuses her "Doll" horribly throughout the story, and flips out when said "Doll" develops an interest in a young man. The "Doll" finally has enough and shows the woman the blood from the injuries inflicted by her and forces her to face reality — she is the woman's totally human daughter. The woman had been gangraped in her youth and the "Doll" was the result of that. The woman imagined that she had aborted her baby and replaced her with a Doll in an attempt to cope with her trauma.
In a Donald Duck story, Scrooge McDuck fires his old butler, and asks Gyro Gearloose to build him a new, Robotic Butler instead, believing it would be more reliable, as well as less expensive. Gyro initially delivers, but Scrooge keeps making demands for expanded features, demanding that the robot — like his old butler — be able to talk, and provide insightful commentary on day-to-day matters. Gyro is stumped, but the problem gets solved when he runs across the old, laid-off butler, who wants nothing more than to get his job back. Final solution: Gyro disguises the butler as a new robot, and the "rental and service fee" for the robot is just about the same as the butler's old salary... the butler gets his job back, and Scrooge thinks he has an infallible robot.
Done another time with Donald ruining Gyro's robot and subsequently dressing in silver-painted box-suit to "impersonate" it. Unfortunately for him, Gyro intended to sell the robot for heavy-duty labour. Of course, the reason Donald borrowed it in the first place was that he wanted to avoid doing household chores.
In the original Magnus Robot Fighter one of his earliest one-shot villains was someone who was obsessed with robotic perfection to the point of having himself coated in metal and acting as if he were one of the robots he idolized to become more like them. After revealing the truth Magnus quickly uses that to defeat him.
In his first appearance, Timber Wolf of the Legion of Super-Heroes was brainwashed into believing he was a robot, only realizing he was human at the end of the story.
A rather subtle example is done in Runaways. Victor Manchez is revealed to be a robot, but his father casually mentions, in the midst of his Motive Rant, that Victor's robotic parts were slowly being assimilated by his human ones. This was done on purpose, with the hopes that when he was an adult, he would go to New York, be mistaken as a superhuman by the Avengers (and not as a robot), and go on to be brainwashed into killing them.
In Invincible, the hero Robot was actually a physically handicapped genius who remotely controlled a robotic drone. By the time of The Reveal, he cloned himself a healthy body and started wearing Powered Armor.
In The Black Hole the Cygnus' compliment of robotic crew members are actually revealed to be the lobotomised remains of the human crew who Reinhardt and Maximilian converted into subservient cyborgs after they tried to mutiny.
In The Wolverine, Wolverine rips off the Silver Samurai's head to reveal Ichirō Yashida inside.
In House of Suns by Alastair Reynolds, an amnesiac android named Hesperas is revealed to be at least partly human underneath his robotic shell. This surprises even him, since he can't remember anything. It turns out that Hesperas, before losing his memory, is serving Machine People as infiltrator to gain access to Vigilance, who aren't interested in interacting with robots.
A partial example in Railsea, when what everyone thought was Naphi's prosthetic arm gets damaged and starts bleeding.
Daleks in Doctor Who. They're mutated Kaleds encased in mobile battle armor.
Tricky in the episode Journey to the Centre of the TARDIS
An internal example occurred in Sliders, where rogue robots were being collected. Two of the sliders were only discovered when they were attacked with hand-to-hand combat, and the robots noticed the blood.
The pilot episode of Barney & Friends had a scene where a robot made from cardboard boxes and a teapot for a head enters a classroom, and as a result it, Barney, and the children start singing a song about a robot that's sung to the tune of "I'm A Little Teapot." (what makes this even more obvious is the fact that the aforementioned robot's head is a teapot) When the song ends, the robot opens up, revealing it to be one of the children that are with Barney.
One episode of Eureka ended with Fargo cheating to win the annual competition to determine who'd built the most realistic robot dog by entering a real dog.
Ocarina of Time features anAnimated Armour Aversion with the Iron Knuckle fought before the boss of the Spirit Temple, upon its defeat it is revealed to be Nabooru.
Similar to the above example, there's a certain cheat one can do that reveals unconscious Gerudo women stuffed in all Iron Knuckles. It's probably just a leftover or something, but it still raises quite a lot of Fridge Horror.
Specifically, half-way through the fight with one, you knock their chest-plate off. IF you're quick with the First-Person look, you will clearly see a Gerudo's chest inside the suit. This is because all the Iron Knuckles are actually just head swaps of the Nabooru model to save precious space on the cartridge since they use the same walk-cycle and attack patterns. It doesn't make the Fridge Horror any less fridge horrory, though.
In the Sonic the Hedgehog series games, Big Bad Doctor Eggman actually captures innocent animals and turns them into robotic henchmen. Defeating said henchmen will cause their robotic shells to come off, setting the animal inside free.
In Gokujou Parodius, the Moon's boss first appears as a kimono-clad bunny girl, which mechanically breaks apart as she gets damaged, only to reveal herself as a puppet maneuvered by a couple of penguins.
Played for horror with the golems of Dragon Age, who used to be dwarves until a Mad Scientist encased them in rock and poured molten lyrium through the slits in the case until they stopped screaming.
A variant in Final Fantasy VII: The Reveal that Cait Sith is being operated by radio. Obviously, Reeve neither fits into Cait Sith itself nor into the moogle doll, but we were led to believe that he was just a normal lifeform anyhow.
Xenoblade: Face Mechon are made by replacing most of a Homs' (read: human's) organs with mechanical parts so that they can operate in what is essentially a Mini-Mecha. Almost every character thought to be killed by the Mechon returns as a Face.
Played for horror in Mass Effect. The Reapers are initally portayed as incredibly powerful and ancient sentient spaceships. Then we find out how Reapers are created: millions of people taken from the dominant race during a Reaper Cycle are liquefied into technorganic slurry that is fed to a Reaper superstructure. Worse, it's implied that the minds of the victims live on inside the Reaper and act as a Mind Hive. When Sovereign claimed that each Reaper was a nation, he wasn't kidding.
In Borderlands2, Angel is revealed to be a Siren, not a Hyperion AI like she previously claimed.
In Metal Gear Rising: Revengeance, after you defeat Jetstream Sam, it is revealed that, aside from his robotic arm, he has almost no cyborg augmentations and was actually wearing a suit of armor. This is made more evident in the Japanese version, where Sam's blood is red, as opposed to the cyborg's white blood.
In Sluggy Freelance, Oasis was assumed for some time to be a robot until she bled during her fight with Gwynn.
Jones of Gunnerkrigg Court is a prime example of Emotionless Girl. Before the story got to finally explain what she is, it was a popular theory — both among the fans, and in-universe — that she was a robot. But she isn't a human, either; she's an immortal, indestructible human-shaped thing. The Un Reveal is that even she doesn't know what she actually is, or where she came from. She's certain about not being a robot though
Happens in Futurama, in a horror movie for robots.
Also spoofed in "Amazon Women In The Mood", where the Femputer that ruled the planet Amazonia turned out to be operated by a fembot, who in turn had escaped from a planet ruled by a male bot operating a male computer. Leave it to the geeks at Futurama to have a machine pretending to be a different machine.
"Do you have any idea what it's like being a fembot in a manbot's manputer's world?"
Also played with in "Insane in the Mainframe" where Fry is released from the Institution for Criminally Insane Robots after being brainwashed into believing himself to be a robot. After everyone else's attempts to convince him of his obvious fleshiness fail, a bleeding cut on his arm snaps him out of it.
The Simpsons’ parody of Robot Wars: After completely failing to build a battlebot, Homer covers himself in armour plating (a mailbox) and enters the arena himself with a hammer. He does pretty well, albeit with numerous horrible injuries, until he has to face a robot so huge it ends up squeezing him out of the suit.
Sideshow Mel: That robot has given birth to a man!
On one Looney Tunes short, Wile E. Coyote consulted a computer to find ways of capturing Bugs Bunny, all of which fail. At the end the computer opens up and out comes...
Bugs Bunny: Of course, the real beauty of this machine is that it has only one moving part.
It gets better. A later episode reveals that the person who was controlling the robot version of himself who was controlling a Powered Armor is himself, also a robot, much to the surprise of his creations. The real man is actually an elderly man by this time, laying in a hospital bed.
Everyone who knows the truth about the Big Guy in Big Guy and Rusty the Boy Robot are careful to keep it secret from the general public, who believe the Big Guy to have a fully-functioning AI instead of simply being Powered Armor. Even Rusty, the Big Guy's sidekick, an actual AI, does not know the truth. When Legion Ex Machina build a duplicate of the Big Guy, they are shocked to discover the truth when the mechanics expect a hatch to open in the "Big Guy's" back.
In one episode of Phantom 2040, one biot turns out to be a disguised human... right after Phantom shoots her, much to his distress since he never kills. She survives.
Eric Cartman manages to fool not just Butters, but every adult he comes to contact with (outside of the Stotches) that he is a friendly household robot from Japan in the South Park episode "AWESOME-O". No one else suspects the cheap cardboard disguise until, at the very end, Eric farts.
Butters: Hey! Robots don't fart!
A minor example in Bucky O'Hare: Jenny uses her psychic/mystic powers on Toadborg, believing him to be a robot. The attack fails, making her realise that Toadborg isn't a machine after all.
The Turk was an automaton, made in 18th century France, that was widely touted to be able to beat any human at chess. Of course, people later found out that it was completely unable to function without a human chess master hiding inside and manipulating the arms. Meanwhile, it was inspiring Charles Babbage and Alan Turing to come up with theorems about universal computing machines, which in turn inspired the first computer programs that could beat the best humans at chess.
Horse_ebooks, twitter sensation and purveyor of Word Salad Humor, was eventually revealed to have been under human control since 2011. It was a true spambot before then.