The hero character gets some sort of apparel or accessory that seems to be great and useful, but it's really unstable, sentient, evil (or at least mischievous in the way Muggles would consider evil) or otherwise damaging to its user's heroic nature.
In the case of a sentient, evil item, it often seeks to turn the hero to its own ends. Toward this goal, it begins manipulating the hero's mind. He becomes less sunny and more grim. He becomes less playful and more violent. Eventually the suit and or its wearer begin referring to themselves as "we".
In the case of unstable or dangerous items, various effects from Applied Phlebotinum can cause the same problems to happen as if it were a truly evil thing affecting its wearer.
At that point, the hero may very well realize there's a problem. Or the damage is done, and the hero's tipped over, and will have to be forcibly separated from his new item. In any case, whether the hero's willing or unwilling, don't expect removing it to be easy.
It needn't always be an article of clothing. It could be a gem or jewelry. In fact, they are often the worst offenders; they are ensorceled to whisper seductively to a prospective wearer, the better to get into position to take over the victim.
This trope has a fine lineage, sharing relations to Mask of Power, Artifact of Doom, Enemy Without, Evil Costume Switch, Evil Feels Good, Clothes Make the Superman, The Hat Makes the Man, Evil Makeover, and With Great Power Comes Great Insanity. The difference is that the person who ends up the maniac in question started out a good guy and had no idea that the article of clothing would drive them evil/insane. Super Trope to Evil Mask. Compare Freaky Fashion, Mild Mind, Paint It Black (where the clothes the person was wearing transform because the person turns evil, rather than the person changing because the clothes were evil).
- The Millennium Ring in Yu-Gi-Oh!.
- The mask that turns its wearer into a host of Darkness in Yu-Gi-Oh! GX.
- Kill la Kill's Junketsu zigzags this. It takes over the mind of anyone who wears it unless the wearer is sufficiently strong willed. Satsuki wears it for much of the series until it's captured and worn by Ragyo, whose mind and Junketsu's are fully aligned, and then used to turn Ryuko evil by forcing it on her. When it's finally returned to Satsuki, Iori repurposes the Kamui by infusing it with Senketsu's life fibers, which were altered by their father to make it compatible with humans.
- The title artefact in Sword of the Reanimator by Junji Ito.
- Spider-Man: The black costume that Spider-Man wore for a while is a sentient and aggressive, if not outright evil, symbiote creature. It used to take his body walking and swinging around while he was unconscious, and its aggression in turn made Peter aggressive and darker. For that matter, this is true of most the spider-suit type symbiotes from the Marvel Universe. Venom is kind of an Anti-Hero (due to the host's morals), but the majority of symbiotes seem to generally bend toward what readers would consider evil. However, it was later revealed that the symbiotes are usually pretty nice originally, but they inherit the personality traits of their previous wielders, changing it into "Maniacs Make the Clothes, and then the Clothes Make More Maniacs" (Venom itself originally bonded with a genocidal alien and then latter on Deadpool, the combination of which drove it insane by the time Spidey got it).
- The Mask removed all social inhibitions while granting huge power. In the comics, it was responsible for several murder sprees.
- Iron Man occasionally lent his armor to James Rhodes or Kevin O'Brien, only to have them turn violent and unstable when it is worn too long because the armor's neural-interface controls were only calibrated for Tony Stark's brainwaves. Obviously, Stark has properly adjusted Rhodes' War Machine armor for him to wear safely.
- Doctor Who Magazine: In "The Blood of Azrael", Azrael's mask contains the memories and powers of the Omnicidal Maniac Azrael, waiting for a host of a suitable mindset to continue his work. Danny provides that host. It's unclear if he was already an Omnicidal Maniac at that point, although he was already a murderous and sadistic xenophobe.
- The evil hat, Doris, from Meet the Robinsons could take over its wearers and produce similar effects.
- Spider-Man Trilogy:
- In Spider-Man 2, Otto Octavius becomes Doctor Octopus as a direct result of the failsafe burning out that was supposed to protect him from the influence of his sentient waldoes.
- In Spider-Man 3, the black suit issue rears its ugly head again, compelling Peter to uninhibited aggression. It's not quite revealed just how much it affects Eddie Brock's mind when it later bonds with him as well, as the theme of mutual revenge is retained.
- The title artifact in The Mask and Son of the Mask is a partial subversion. It is an item of Loki, god of mischief. So when it takes over the gentle dreamer Stanley Ipkiss, it boosts his confidence and turns him into a mostly-harmless cartoon maniac, who indulges in one act of strongly implied horrifying violence. Dorian, however, is bitter and violent, and the Mask only magnifies those bad traits to worse.
- The House That Dripped Blood: In "The Cloak", whenever Paul Henderson don the eponymous cloak, he turns into a vampire.
- Most of the rings in The Lord of the Rings, The One Ring being the most focused on, but most pronounced in the Nine; they turned their owners, once proud kings, into evil ghostly death knights.
- The Seven Rings were meant to do the same to the Dwarves. Unfortunately for Sauron, while the Rings did magnify their greed and some other negative emotions, they did not prolong the lives of the Dwarves, nor did they turn the Dwarves into wraiths as the Nine Rings did to the humans. So Sauron sought to take the Seven Rings back; he managed to get three, while the other four were destroyed by dragons.
- Averted with the Three Rings of the Elves; these Rings were never touched by Sauron, and were wielded by immortal beings who were not subject to the "unduly prolonged life" effect that the Great Rings all had. The Three were still subject to The One Ring if a sufficiently powerful being gained possession of it, however.
- The locket Horcrux in Harry Potter and the Deathly Hallows.
- The Haunted Masks in the Goosebumps series.
- The Archchancellor's Hat in the Discworld book Sourcery. Played with in that the wizards weren't really on the bad side, just one of two sides wreaking havoc equally, and that the person who got the hat was already a scheming Evil Chancellor and probably couldn't have gotten worse. But still, the hat has a mind of its own, and not a nice one.
- The amulet version turns up in Stephen King's book Needful things.
- Clark has stumbled upon jewelry made of red kryptonite at least three times on Smallville, usually to the detriment of his personality.
- Honey, I Shrunk the Kids the Series had the Thinky-Ring, which turned the wearer into a psychic vampire that grows smarter by draining the intelligence of other people, not to mention addictingly evil. Wayne's wife went so far as to call the ring her "precious," a reference to The Lord of the Rings (the novel; This was years before the movie version), and when his son wore it he dressed up in a black robe and used a growth ray to enlarge his cranium.
- Linda's magic hat from the Round the Twist episode "Copy Cat".
- The ring from "The Wedding Ring" episode of Amazing Stories turns any woman into an Ax-Crazy Knife Nut as well as an irresistible seductress. Its last known owner was "The Black Widow". Makes you wonder if her evil tainted the ring, or if she was another victim of the ring.
- The Twilight Zone (1985): In "Dead Woman's Shoes", a shy woman tries on a pair of high heels at a thrift store that make her assertive, self-confident-and send her on a murderous mission.
- Doctor Who: In "The Keeper of Traken", Kassia is turned evil by the necklace the Melkur gives her, though in this case it's a mind control device.
- Warhammer 40,000 brings us suits of armor corrupted or even possessed by daemons, with... predictable... results for anyone who dons them.
- In Graham McNeil's novel Storm of Iron, a daemon lures Larana Utorian into donning one. True, she does get to kill the Beserker who wore it before her — but then it starts to get control of her.
- Some artifacts in Dungeons & Dragons have a tendency to do this. But then again, what were you expecting from an artifact that requires you to gouge out your own eye (or chop off your own hand) in order to use it?
- This can be true of any intelligent magic item (and pretty much any item can be intelligent). Each such item has a Character Alignment of its own as well as an "Ego Score" measuring how strong its personality is. An evil item with a high Ego Score is this trope waiting to happen; if wielded by someone it disagrees with it can refuse to work, or attempt to control the user. Of course, it can also be reversed; a good-aligned item might attempt to control an evil user as well.
- Exalted has a sort of demon called a Perronelle, an amorphous creature that can be worn as a suit of flexible, lightweight, durable armor...if you don't mind it whispering incitements to blasphemy and Yozi-worship in your ear while you sleep.
- Rifts: Mercenaries features the Angrar Mark 1 suit, which, like the Mark 2, will slowly corrupt its wearer, causing demonic features to appear on them and leading to violence if anyone is caught near their armour; until eventually the person is absorbed by the suit as the suit itself is actually a demon.
- In Warcraft III, the cursed sword that Arthas finds in Northrend, Frostmourne, is what destroys the last straw of his sanity, leading him to become a Death Knight and eventually the Lich King.
- Luxaren Allure: The Armor of Ellicide, which turns Aurelie into Evil Overlord Darkloft.
- In Fate/Grand Order, Antonio Salieri's warped by rumors into an Avenger. As part of this transformation, he's given a twisted costume named the Wailing Facade, which grants him considerable power and even a Noble Phantasm at the cost of turning him into a Mozart-hating psychopath. He's aware that he's not the real Salieri, who was in life a good friend and peer of Mozart, but he's not strong enough to sustain the existence of a Heroic Spirit without the costume.
- Wonderella's black dress in this strip of The Non-Adventures of Wonderella is a parody of Spider-Man's black costume. But hey, it was 70% off!
- Darken's Komiyan seems to be heading in this direction. His sword is certainly trying to push him down that road, and is capable of taking over his body.
- A modest example with Walter from Dubious Company, who varies between Type 2 Hollywood Nerd and A Pirate 400 Years Too Late depending on his clothes. He almost freaks after a spell sends the cast appropriately dressed to a beach.
Walter: What do I look like? A mage? I have no clue. Hell, I'm not even a pirate right now!
- Dolly Malestrom in the Ciem Webcomic Series, upon stealing the Earwig prototype suit, immediately goes from the not-so-humble housewife to a crazed and psychotic slayer of street thugs. So crazy, she's able to take on an anti-villain who should be several weight classes beyond her.
- In the Hyperbole and a Half post "Menace", Allie recounts how a dinosaur costume made her four-year-old self go mad with power.
- See the Spider-Man entry under Comic Books. Every version of a Spidey Animated Series after the 80s has done a variation on the black suit saga.
- Jenny's "human skin" on My Life as a Teenage Robot was fixated on being normal and beautiful and refused to let Jenny use her robot powers to save people when the situation warranted.
- A police officer on Superman: The Animated Series is a milder example. He was given a combat suit to use that ended up addicting him. He shaved his head, the better to interface with it, began referring to himself as "we" and got violent when separated from the suit or thwarted from using it. It also made him territorial to the point of being willing to beat up on Superman.
- Cash on Ben 10: Alien Force ended up with one, in the form of a cybernetic robot glove that could build itself a new body and compel its wearer to mindless violence.
- The mother of Manny Rivera, the protagonist of El Tigre, is recovering from an addiction to a pair of gloves she wore as the superheroine Plata Peligrosa, that turned her into an action junkie.
- In Danny Phantom, there was a cursed necklace that turned its wearer into a raging dragon —literally—when the wearer became upset.
- The invisibility suit used by an already slightly unbalanced man in one episode of Batman: The Animated Series became toxic when it was activated and apparently drove him completely over the edge into complete psychopathy.
- Fang of Dave the Barbarian once acquired some lederhosen that gave her super-strength, but turned her evil. From this, and her rescue from them, she learned the valuable lesson that Dave has really tender eyebrows.
- In The New Adventures of Superman episode "The Wisp Of Wickedness", a possessed hat causes anyone who dons it to commit evil acts.
- Used in one of the Halloween episodes of The Simpsons. Homer receives a toupee made from the hair of executed criminal Snake, and it forces him to seek revenge on those who helped put in him jail. Specifically, on Bart.
- Now now, he did kill a couple others too, Bart just proved to be harder to murder. Just ask Sideshow Bob!
- In "Team Homer", the elementary school institutes a uniform policy, and the drab clothes causes the kids to regress in personality so much that that they blink in uniform. Then it turns out that the uniforms aren't colorfast, and during a rainstorm during recess, the clothes become tie-dye, setting off a riot.
- In an episode of TMNT: Back to the Sewers, an antiques store owner hastily gives Casey Jones the evil Ring of Yin to keep it out of the hands of the Purple Dragons. Not knowing what it is, Casey gives it to April as an engagement ring. It rather quickly possesses her and turns her into a powerful, monster-summoning demon. Casey, being the one who put it on her, is magically bound to be the only one capable of removing it. No small task, as by the time he is told this April had grown to epic size and was flying over the city.
- Gargoyles features the Eye of Odin, a necklace that turns its wearer into a living embodiment of their darkest impulses. Even in human form, they are incredibly reluctant to relinquish it.
- Inverted, sort of, in the Invader Zim Christmas episode, where the already-evil Zim makes a robotic Santa suit that takes him over to make him jolly and Santa-ish. Played Straight later when the suit goes crazy and turns into a psychotic monster; it flies off into space and apparently terrorizes the Earth every Christmas one million years in the future.
- In Iron Man: Armored Adventures, the Living Laser and Madame Masque both slowly went insane and became terminally ill as a result of the unstable ore in the Howard Stark inventions they used to give them powers.
- Adventure Time: The Ice King's Crown. Centuries prior, Simon Petrikov, an collector of ancient artifacts, purchased the crown for his collection, and put it on momentarily as a joke when showing it to his fiancee. However, the crown's power never left him; although it granted him immortality and amazing power over ice and snow, it slowly drove him insane, transforming him into the Ice King.
- In "Little Dude", Finn's hat gets brought to life to by a spell that infuses it with an evil spirit. It then starts forcing itself onto people's heads and turning them evil.
- The Looney Tunes cartoon "Bugs' Bonnets", in setting up its The Hat Makes the Man premise, invokes this by putting a meek suit-wearing everyman in a pirate outfit, with this result:
Man: (waving sword and flintlock) Batten down the keelhaul! Kill the women and children first! Blood!! Gore!! Hang 'em from the mizzenmast!!! (stands there panting with a crazed grin until costume is removed)
- Camp Lakebottom: In "Remember Fort Sunny Bottom", the stone hat from the statue of General Butt falls on Buttsquat's head; causing him to be possessed by the ghost of the general and declare war on Camp Lakebottom.
- Kung Fu Panda: Legends of Awesomeness: In "Kung Shoes", Po buys a pair of magic shoes that enhance his kung fu prowess. However, if the wearer wears the shoes for more than two hours at a time, she shoes start to take over and demand that the wearer do more and more kung fu until they have destroyed everyone and everything around them.