In Soul Eater a student named Crona debuted in the series by attempting to kill the two protagonists. This was because Crona was infected with a substance called Black Blood, which is a blood replacement fluid that can be controlled by a human weapon, which sacrifices the user's sanity for invincibility. After being restored to sanity, Crona was allowed to attend the DWMA, but as of recent chapters has been recaptured and rebrainwashed by Medusa and in chapter 104 was revealed to be the series Big Bad, much to the dismay of characters and audience.
Until chapter 106, anyway.
In the Majin Buu arc Dragon Ball Z, it is Vegeta who is brainwashed and made to fight against his former allies. The brainwashing also gives him a major power boost. In fact, that's why Vegeta decided to let Babidi take control of him: so that he could be on even ground with Goku at long last. He eventually manages to break free of the mind control, but the trope is subverted before then, as Vegeta reveals that he could break free at any time.
It is played in Dragon Ball GT when Baby controls almost all the Earth population. The only ones that weren't controlled were Goku, Pan, Mr. Satan, Majin Buu and Uub.
In the second movie, Piccolo is captured by Dr. Wheelo and Dr. Kochin and forced to fight Goku.
In the Garlic Jr. filler, the black water mist does this to all the supporting characters, turning them evil. Piccolo and later Krillin fake being infected, in order to free the currently captured and bottled-up Kami and Mr. Popo.
It happened several times in the Mazinger trilogy:
Mazinger Z: The Hero Kouji Kabuto was brainwashed by Viscount Pygman, and later by the Vegans in the UFO Robo GrendizerGo Nagai manga, the UFO Robot Grendizer tai Great Mazinger movie and Super Robot Wars MX in Chapter 10. Professors Morimori, Sewashi and Nossori also were brainwashed by Baron Ashura into one of the earlier episodes of the original anime series. AND in another episode three workers of the Institute were brainwashed into piloting several Mechanical Beasts.
UFO Robo Grendizer: Brunhild, Duke's best friend back in Fleed was brainwashed by the Vegans into murdering Duke. Also, Kouji and Tetsuya were brainwashed to destroy Grendizer with their own Humongous Mecha.
Chazz/Manjoume in Yu-Gi-Oh! GX was brainwashed by the Society of Light and sent to force-recruit everyone else at the Academy, including his friends. Not quite the same, but considering the Society was an apocalyptic cult, it might as well be.
Happened to Misawa and Asuka as well. In Asuka's case, she was much more dangerous because she was serious about it, unlike Manjoume's "I've seen the light!" cult ranting. Meanwhile, Misawa released himself by realizing that what he thought he wanted wasn't what he really wanted after all. He thought he wanted to be taken seriously as a duelist, when his real gifts and strengths lay in the realm of duel physics. As soon as he stopped trying to be something he wasn't (a potential pro duelist), he was a lot happier and more confident with himself.
In fact, Saiou himself, the leader of the cult, qualifies, maybe especially so. He was brainwashed by the greater evil directing the cult and became its pawn. At times, there was a conflict within him, and occasionally, his sanity broke through temporarily (at one point, causing him to give the two keys to his doomsday device to Judai and Edo and warn them never to give them back to him) but his madness always returned until the climax of the arc.
In Yu-Gi-Oh!, Marik brainwashes Jounouchi and Anzu. Marik released Anzu only when she put herself in a Death Trap whereas Jonouchi broke free over the course of the duel with Yugi. (note that in the original Japanese and Manga, Jonouchi's mind became very unstable after being Brainwashed, adding to this trope further).
There's also Shadi, who uses his Millennium Key to brainwash Sugoroku's friend Professor Yoshimori into attacking Yugi's friends in the manga. In the Toei series, Shadi brainwashes Honda instead... he'd already disposed of Yoshimori prior.
Let's not forget about Dartz doing this to Mai. Even worse, Dartz himself is brainwashed by the Orichalchos.
Ranma ˝: the super-ninja Konatsu is brainwashed by his Evil Stepmother (who bears a scary resemblance to Edward G Robinson) into attempting to kill Ranma. It is only the Power of Love that undoes it.
The Phoenix People are also able to use something like this (or possibly More Than Mind Control); they have magical eggs that they can throw at people, which then expand and envelop the person. When the egg is cracked open (it doesn't hatch otherwise, but thankfully seems to put the victim in a state of suspended animation), the victim "imprints" on the first person they see, becoming their helpless slave. Kiima does this to Shampoo and then orders her to kill Ranma. To her credit, Shampoo manages to ask Ranma to instead allow her to use one of the eggs on him, so that she won't have to fulfill her orders, but Ranma (understandably) refuses. She then attempts to get Ranma to have sex with her (whereas, up until now, she's always aimed for romance and at one point actually got offended when she was made out to be trying to seduce him), going so far as to threaten Akane Tendo's life to make this happen. Ranma cures her by sticking her in another egg, and Mousse then shows her a mirror, so she imprints on herself. She later cures Genma, who she had managed to capture in an egg of her own, by telling him to snap out of it.
This was the modus operandi of Goldie Musou in multiple arcs of the Gunsmith Cats manga. It's explained fairly well by her use of the drug Kerasine and her skills in hypnotism to convince her tools that their targets (ranging from complete strangers to beloved family) are possessed by demons, shapeshifting aliens bent on conquest, and the like. Indeed, the murders often cement her hold, by making a return to reality too painful for the subconscious to permit.
This happens to poor Inuyasha an awful lot, given how many times he gets forced into his homicidal full demon form by various villains.
Happened to Kagome once, when Tsubaki the evil Miko contaminated the Shikon no Tama shards with her own dark energy. She then tries to make Kagome attack Inuyasha with her own arrows, despite Kagome's own struggles to not harm him.
In Sailor Moon, Mamoru was at least twice brainwashed into doing this to the Senshi. in the Stars manga, Sailor Galaxia does this not only to him, but to all the Seishi who are mind-controlled to attack Usagi. In the manga, it's made abundantly clear that the senshi are actually already dead.
Ami is also brainwashed in a R episode where she is made to think all of her friends hate her for being a nerd. She sees through the ploy and blasts the monster.
Also in Sailor Moon R, Chibiusa is brainwashed into attacking the rest of the cast, and is made to believe everyone hated her (thanks to the Big Bad altering her memories/taking out important bits of them).
There's also Professor Tomoe in the anime, who gets brainwashed and crazy as a consequence of a Deal with the Devil with Big Bad Pharaoh 90 to save Hotaru from death.
In the Stars anime, Haruka and Michirupretend that they are brainwashed by Galaxia to actually attempt to fight her (going as far as killing Setsuna and Hotaru with their own hands) but fail and ultimately die. This event is redone multiple times in the musical adaptations based on the Stars series.
Mikoto Minagi in both incarnations of Mai-HiME. In the anime, she is controlled by a pendant similar to the one worn by her older brother Reito, who himself is possessed by the Obsidian Lord, and in the manga, she's possessed by one of the spores from Shiho's CHILD, and attacks the heroes as they attempt to rescue Mashiro from kidnappers. Talk about unlucky. In both versions, she is saved by a Cooldown Hug from Mai.
In GaoGaiGar FINAL, Guy is captured and chemically brainwashed into a berserk destroyer by the villains, placed in a copy of his Humongous Mecha GaoFighGar, and sicced on Sixth Ranger J along with similarly reprogrammed copies of the rest of the robot team. Right as Repli-GaoFighGar is about to Drop the Hammer on King J-Der, the Repli-Nakama resist the reprogramming and sacrifice themselves to stop Guy and give the remaining heroes a chance to get him back.
In the original series, all four of the machine kings are all subject to this trope, with all eventually getting redeemed some time into the show, with Primada and Polonaise suffering Redemption Equals Death sort of, while Pizza and Penchinon both get restored to their original forms, Soldato J and the main computer of the J-Ark, respectively.
Both the Crystal Saint (anime only) and Leo Aiolia in Saint Seiya. Their brainwashing was so through that it took death to release them. Crystal had to die, Aiolia had to see someone else die. Both cases end up in tears.
This is what happens to four of the main characters Gainer, Cynthia, Gauli and Sara in Overman King Gainer forcing the last main character, and the supporting cast to fight the Overdevil and them at the same time.
Stella, who is really just emotionally fragile and naive, but is brainwashed into freezing up or panicking whenever someone mentions death, and to calm down and absolutely trust anyone who vows to protect her. After being programmed and deprogrammed so many times by Phantom Pain, then Shinn, then Phantom Pain again, her main response now is to go crazy and panic over anything she even loosely relates to death. Which is bad if she's at the controls of a truly giant mecha with about fifty-bazillion Wave Motion Guns and no-one can talk her down.
Actually, this one is More Than Mind Control. Tasuki was holding back his one-sided feelings for Miaka, which let the Big Bad control him easily.
Ikuto from Shugo Chara!when controlled by his evil jerkass of a stepfather and forced to transform into Death Rebel. He's not necessarily crazy when brainwashed at first, just rather cold and emotionless. But, sadly, the control over him eventually escalates to he point where he's trying to murder his childhood friend Tadase and the girl he loves, Amu. Luckily, in more recent chapters of the manga, he's shown to be back to normal thanks to Amu.
In the Kirbyanime Knuckle Joe's father, a renowned Star Warrior, is kidnapped and brainwashed by Nightmare himself. He is sent to attack his former allies, and his best friend Meta Knight is forced to kill him.
Jellal, a massive expy from Fairy Tail, is made out in flashbacks of when he was a kid to be perfect hero material. He has a strong sense for justice, he risks everything for his friends, and he doesn't bow down to the enemies. At the time the story begins, though, he's trying to revive the Fairy Tail world equivalent of Voldemort using forbidden resurrection magic by sacrificing his childhood friend. Three guesses why.
Also in Pokemon Special, Blue during the RGB arc and revealed to be the reason that Bruno is in the Elite Four.
Arguably, also happens to Celebi in the fourth movie.
Happens to Pikachu a few times: Once from Cassidy and Bunch ("Pikachu Re-Volts"), thrice from Colress in the N arc. And when his Nice Guy tendencies are subverted, he gets scary.
In the manga series Zodiac PI, Lili's rival, Sirius, is brainwashed into trying to kill her, her friend, and her father. Finally broken thanks to both The Power of Love and the shock of cold water.
In Monster, Gillen hypnotizes Nina in order to draw out her childhood memories. She refuses to tell him anything, and attempts to strangle him for good measure.
In a Bleach filler arc, the zanpakuto of most or all of the soul reapers in Soul Society are turned against their masters by a rogue zanpakuto named Muramasa.
This happens to Rukia in the third movie thanks to Shizuku and Homura.
And this is also the modus operandi of one Shukuro Tsukishima, who does this via using his memory-altering powers to convince his victim that he's their dearest person ever.
Later, the Vandereich either brainwash Jidanbou and the Mission Control squad members into killing each other so they can't relay information anymore, or use them as People Puppets so they start killing each other.
In Hekikai No Aion, the mushis infect a human host. The victims look normal but them become this when they take a look at Seine's face.
DG Cells have this effect in Mobile Fighter G Gundam. Once the metal plague gets into the victim's brain, they become subject to the Dark/Devil Gundam's will. It's also known as the Devil Gundam's ability to self-multiply.
Lucifer in Angel Cop. Already a powerful psychic she'd actually volunteered to be experimented on and turned into a psychic super soldier because she believed she was helping mankind. Sadly, she's brainwashed to the point that she believes viciously murdering innocent people and her former allies who woke up from the brainwashing is all for humanity's sake.
Chiho Masuda in Variable Geo was brainwashed into an assassin in order to kill or at least delay the heroes.
There are also several cases of More Than Mind Control; specifically Benimaru, Mai and Leona. In the first two cases, their inner struggles are greatly amplified by Goenitz's powers and they're sent into temporal Unstoppable Rages; in the third, Goenitz himself awakens Leona's Orochi blood.
In Toriko, Joa the Dark Chef has this power. Joa can "cook" others with a few slices to alter their "flavor", changing them into completely different people. Teppei falls victim to this and is now an emotionless fighting machine under Joa's command.
In Kill la Kill, Ragyo's Mental Refitting forces special Life Fibres called Marionette Threads into her victim's brain, turning them into mindless drones that do her bidding without question. In Episode 18, we first see this used to enslave the entire 1-Star student body of Honnouji Academy. Made even worse when she used it on Ryuuko. She managed to fight it off, though, and physically pull the Marionette Threads out of her own brain with her bare hands!
This also happens when somebody is "worn by their clothes", and the Life Fibres in their garments forcibly bend the wearer's will to their own. This happens to Ryuuko when she's forced to don Junketsu in Episode 20.
The eponymous drug in Banana Fish is used to brainwash people into doing things they would normally never do, including committing suicide or attacking their friends.
In Cable & Deadpool, Deadpool is brainwashed by the Black Box to kill the biggest threat to the public safety. After managing to convince Deadpool that this is not a) clowns; b) Simon Cowell; c) Galactus; or d) Karl Rove, Deadpool goes off to kill Cable, who he sees as the next biggest threat. After fighting Prester John and then going through several alternate universes in order to find (and save) that person, he then gets back and tells everyone that he was only looking for him to kill him. He is restrained until the others can remove the effects of the brainwashing.
If you understand DP at all, a), b), c) and d) shouldn't have been too much of a surprise.
In Y: The Last Man Yorick's sister Hero falls under the influence of Victoria, the man-hating cult leader of the Daughters of the Amazon, so much that she's prepared to kill her own brother, as well as shooting a young girl in the head on Victoria's order. Even after Victoria is killed Hero still has her voice inside her head.
An old World's Finest comic in which Batman is brainwashed into being a sadistic warder at a prison for Superman has him reflect that hypnotism cannot make anyone do something against their nature, before the narration explains "But this is super-hypnotism, of a kind never before experienced by anyone on Earth!" (It's almost a shame that this was written in the days of simpler storytelling, as a modern telling of the story would have it revealed that Batman would certainly be a warder on Superman's prison if he thought Superman went rogue...)
The brainwave scanner in the G.I. Joe comic was a feared—and painful—method of brainwashing. It could eventually be broken by a strong-willed individual, and if one was a master of the "Arashikage mind-set" one could free others as well.
This sort of thing seems to happen to Superman on semi-regular basis.
Probably the fact that Superman is glaringly not immune to magic and mental powers, coupled with the possibilities inherent in showing just how badass a character is by having him/her hold off frickin' Superman while at the same time giving the character in question a good reason for why they're fighting a good guy, makes this kind of story just too big a temptation for comic writers to resist.
Mr. Negative, a new Marvel villain on the block since Brand New Day, has this of a superpower to do to other people. Inverting their colour scheme, and having them proclaim glory for Mr. Negative while beating the tar out of others they're sent after.
Superboy gets a heavy case of this in Teen Titans, courtesy of his genetic progenitor Lex Luthor. Highlights include shaving his head, cutting an 'L' into his T-shirt, and kicking the shit out of the entire team.
One storyline in X-Factor concerned a villain using brainwashed and crazy assassins to kill targets — including a woman's own mother, Monet, and Shatterstar.
Lady Blackhawk was brainwashed by Killer Shark into becoming the villainous Queen Killer Shark in the Silver Age and it was even hinted that she had a sexual relationship with Killer Shark when she was brainwashed.
Thor has been turned against his allies many times over the years, usually delivering a Curb-Stomp Battle until he comes to his senses.
During the "Ends of the Earth" story arc, Doctor Octopus does this to all the Avengers at once, but is tricked into increasing this to Villain Override over Thor, which renders him unworthy to wield his hammer.
In the Sonic The Hedgehog comics, this happens twice during the Iron Dominion arc: First, the Iron Queen uses her Magitek powers to take control of Monkey Khan and use him to destroy the Dragon Kingdom Freedom Fighters. Then, she uses those powers to reprogram NICOLE and use her to effortlessly take over New Mobotropolis. Khan was released by the Queen when she didn't need him anymore, and NICOLE was soon returned to normal by Sally (though she continued to pretend to be brainwashed for a while).
And earlier, during the "Enerjak Reborn" arc, Knuckles was brainwashed by Dr. Finitevus into absorbing the Master Emerald's power and becoming the new Enerjak. It took his father's Heroic Sacrifice to snap him out of it.
All Fall Down: Along with receiving a new pair of legs, Pronto is conditioned to attack his closest friends, and to love the idea.
The title character of The Punisher, Frank Castle, premiered as a vigilante who kills criminals. Writers who disagreed with the concept sometimes took it, and Castle over the top, having him kill or attempt to kill petty criminals such as jaywalkers. When Marvel made the decision to give The Punisher his own series, they had to retcon this to make him acceptable even as a dark hero. So they declared that during his crazy periods he had been under the influence of mind-altering drugs.
In Death Of The Family, Damian "Robin" Wayne finds himself facing...his father Batman?! Ultimately subverted: it's a martial-arts master in costume who fell behind on a debt to Joker. However, Joker does come dangerously close to pulling this on the entire Batfamily.
In Hex, Jonah's girlfriend Stiletta was kidnapped and brainwashed into become a bloodthirsty competitor in the Gladiator Games. Jonah is later forced into the arena and Stiletta attempts to kill him.
In Gothtopia, The Scarecrow has all of Gotham in a gas-induced hallucination, making them think everything is wonderful while attacking anyone who thinks otherwise. This includes the heroes, they eventually break free of the hallucinations and try to figure out what's going on.
Laura Kinney aka X23 falls victim to this whenever she is exposed to the Trigger Scent. Thanks to the Facility's conditioning, Laura suffers a Pavlovian response to the scent that makes her into a true Living Weapon who will not stop until the people marked with the scent are dead. She blacks out all conscious thought during these times and only comes back after the scent is gone. Just to illustrate how powerful her response to the scent is, in her origin story Innocence Lost she killed the only two people she ever really cared for and who cared for her under the influence of the scent. She also nearly killed her aunt and cousin who only survived because they were able to wash off the scent in time. Emma Frost once claimed that the Trigger Scent response is so deeply ingrained in Laura's brain that Emma can't remove it with her Psychic Powers.
Yamane Jun from Kyon Big Damn Hero. Bizarrely, the brainwashing was completely unintended and it's dubious if the brainwasher even knew of their existence.
Averted in With Strings Attached; Bayanis orders the ensorcelled Paul to go kill the others, but whoops, it turns out he's been faking it all along and ties her up instead.
All of the ghosts in Sweetie's Mansion are under the control of Specter Yield including the ghosts of the Mane cast. All of them, save for Ghost!Fluttershy, are happy to carry out the order to capture or kill Sweetie Belle to become a ghost, until they are brought back to normal.
In the MLP AU story Rainbooms and Royalty, Shining Armor, two of his pegasus guards, and Ditzy Doo/Derpy Hooves are all corrupted into Nightmare Moon's servants — the former as her Dragon, the latter three as the first Shadowbolts.
Thanks to Danzo, this happens to Hinata in Naruto:Asunder. In her case however she channels the crazy (along with lust) to one person and only one person: Naruto.
In the climax of Paper Mario X 2, shortly after taking over Peach's body, the Shadow Queen brainwashes Zelda and Amy to be on her side and fight their friends. The others (especially Link) were not happy by this.
Link: It's one thing to possess one girl, but three is definitely crossing the line!
The Disgaea fanfic The Curse of Blood has the mother of Laharl controlled by original charcter, Milady. Later on a previously killed Laharl becomes mind controlled as well.
Queen Of All Oni: During the second half of the story, Jade abducts Viper and force feeds her Ikazuki's chi, transforming her into the Shadowkhan General Hebi, who's conditioned to be utterly loyal to Jade.
Fallen King has Yami Bakura brainwash Tea to attack Joey and Tristan, thanks to the Change of Heart card.
Pokeumans: Minions of Pokextinction are fanatically loyal to Mr. X and his ideals, thanks to a little mind control.
In Mega Man Recut, this happens to any robot affected by Wily's reprogramming gun.
In Crowns of the Kingdom this happens to King Louie and his servants, who are brainwashed by the Dispirations.
Graduate Meeting Of Mutual Killing implies that Nebulous Evil Organization Diavolos Avante uses an early version of the Junko Enoshima AI to brainwash the Main Board members. The exact purpose is unclear for now, but it's hinted that it may be to break down any moral inconveniences the Board Members may have.
Missingno and 'M end up possessing numerous beings and having them attack the proto-J-Team during the J-Team Assemble Saga.
What happens what Pokémon are Mind Raped into becoming Shadow Pokémon.
Mirrors Image: Princess Celestia, of all ponies, thanks to the previous Changeling Queen being a Knight Templar Parent. Usually whenever something triggers it, she suddenly enters an Unstoppable Rage and tries to petrify whoever's standing in front of her. Like say, Twilight Sparkle. Even worse, any attempt to remove the brainwashing also triggers it, which is bad news for one unfortunate doctor (though he manages to avoid being turned to stone).
Later on, Prince Blueblood thinks this is what's happened to everypony else, and refuses to believe otherwise. It doesn't end well.
Films — Animated
In Despicable Me 2 Eduardo and Dr Nefario kidnap some of Gru's Minions and mutate them, turning them into mindless, indestructible monsters. This is reversed later by Nefario's antidote
Disney-Pixar's Toy Story 3, when Lotso has Buzz reset into demo mode and convinces him that Jessie and co. are enemy prisoners. Later, when Woody returns to Sunnyside to save everyone, the gang tries to re-reset him and somehow turn him Spanish.
In Wreck-It Ralph, it's later revealed that the Sugar Rush characters were made like this thanks to King Candy, who is actually Turbo in disguise, hacking into the system and turning Vanellope into a glitch.
In the Sakura Wars movie, Orihime Soletta gets ambushed by Patrick Hamilton, who then brainwashes her, and later controls her to fight the other members of Flower Division. She snaps out of it after her fire energy attack that meant for the Flower Division blows up and wrecks her Eisenkleid. She then says to Leni (Reni) after regaining consciousness, "I'm so sorry. I guess I really blew it this time."
In How To Train Your Dragon 2, Toothless gets brainjacked by the King/Alpha Dragon. Starts off with him attempting to kill Hiccup — Stoick pushes him out of the way and takes the fatal hit. Later, Toothless serves as Drago's mount until Hiccup saves him with The Power of Friendship.
Films — Live-Action
Probably the most iconic example is Cesare from The Cabinet of Dr. Caligari, who is hypnotized into killing people in his sleep as part of a psychological experiment. Or is he?
In the first The Naked Gun movie, Reggie Jackson is brainwashed to kill Queen Elizabeth II during a baseball game, and Jane Spencer is brainwashed to kill Frank Drebin. (And later in the series, she'd inflict upon him a fate worse than death: marriage.)
The central plot of Woody Allen's The Curse Of The Jade Scorpion. Allen and his prickly female counterpart are hypnotized at an office party. What at first seems like a simple joke (the hypnotist makes them pretend to be newlyweds on their honeymoon) is really a plot to make them rob their employer on the hypnotist's behalf. Lampshaded in that another character points out at the end that you can't make a hypnotized person do anything they don't really want to...
In the 1994 movie The Shadow, Shiwan Khan sends a mind-controlled Margo on a mission to kill the Shadow. The Shadow breaks her hypnotic trance after she mistakenly shoots a mirror showing his reflection. Margo realizes that, despite Khan never mentioning The Shadow's name, it was Lamont Cranston she tried to kill, because Lamont and The Shadow are one and the same. It turns out that Khan counted on her learning The Shadow's identity, though he didn't count on The Shadow not killing her to keep it a secret.
Done to Nightcrawler with a mind-control serum in to make him kill/try to kill the President (it's not clear if he was meant to succeed or die in the attempt). He snaps out of it and escapes when a bodyguard shoots him. This is also done to Cyclops later in the movie and had already been done to Deathstryke.
Also Charles Xavier, by William Stryker's mutant son Jason, who is himself Lobotomized and Crazy.
In X-Men: Days of Future Past, the Prototype Sentinels were constructed entirely from polymer, but Magneto controls them through metal he fused to their components.
The major plot point of Zoolander is that Mugatu offers Derek a trip to a "day spa" to prepare for his runway show, the spa is actually a facility where Derek is brainwashed to attack the Malaysian Prime Minister when the song "Relax" by Frankie Goes To Hollywood is played. Makes Sense In Context.
In TRON: Legacy, Tron attempted to hold off and defeat Clu while Flynn escaped, seemingly being derezzed in the process. In actuality, Tron was brainwashed by Clu into becoming Rinzler, and evidently became a merciless killing machine until Flynn wonders what Clu did to him during the chase, in which he regains his original memories and turns against Clu.
During one scene in the Firefly movie Serenity, River, the resident heroic Ax-Crazy and whimsical-in-the-brainpan Woobie, is exposed to a subliminal message buried in a Fruity Oaty Bars commercial. This activates River's deadly martial-arts-killing-machine programming put into her mind by the Alliance, and she proceeds to methodically wipe out a whole bar full of people, even taking down Jayne when he tries to restrain her, and is only stopped when her brother intervenes with a code-phrase in Russian that serves to put her to sleep.
The 2012 Avengers film gives Loki the ability to easily turn people over to his side by tapping their heart with his scepter. Unusually for this trope, the brainwashing seems to simply change their perspective on the world rather than actual mind control or manipulation, and they maintain their usual personality and knowledge while working for the other side.
It utterly fails when he attempts to do it to Tony Stark, thanks to his Arc reactor blocking the heart. All we hear is a "ding" of metal on metal. Tony makes a joke about "performance issues", further pissing off Loki.
In the first Wishmaster, a cop wishes that a criminal who has gotten away on seven counts for a crime (not stated what kind) would just commit something that the cops could easily nail him for. The Djinn then controls his body from a distance, and causes the guy to turn into an almost-supernatural killer who immediately grabs a cop's gun and starts a shooting frenzy in the police station. He kills a half-dozen cops before he dies from his own wounds.
In Videodrome, Max eventually becomes compelled by the Videodrome tapes to murder his partners at Civic TV in cold blood. When he goes after Bianca O'Blivion, she reprograms him to kill her enemies (the people who programmed Max to become an assassin in the first place) for her.
In Cube Zero, Haskell is remotely reprogrammed by activating the military chip placed into his brain from when he was a soldier. He tries to kill Wynn and Rains before they escape him.
Played with in Angel Heart. Johnny/Harry kills several people under Satan's influence, but it's left deliberately vague whether the Devil is directly compelling him to commit the murders or if he's allowing Johnny Favourite's vile personality some freedom to indulge in these acts and Johnny is keeping Harry from finding out the truth about himself.
One early example is Richard Condon's book (twice adapted to film), The Manchurian Candidate, wherein a group of soldiers captured by the Chinese in the Korean War are brainwashed. (The term brainwashing is, in fact, believed to have originated during the Korean War, in reference to the coercion that the Chinese would use on prisoners.) One of them becomes a Manchurian Agent for the Chinese, against his will and without his knowledge.
Dean Koontz used this in False Memory, in which the victims had two sets of code words to prevent accidental triggering: a particular haiku (specific to each person), and the name of a character - sometimes a very obscure character - from The Manchurian Candidate.
Also used in Night Chills and in a way in Mr. Murder where the assassin Alfie is controlled by a special phrase.
Peeta in The Hunger Games, using a toxin that causes any memories invoked while under its influence to be associated with intense feelings of fear, and therefore making anyone included in those memories (in this case, Katniss) seem like a threat to be destroyed.
Appears several times in literature set in the Warhammer 40,000 'verse. Unusually and unfortunately, killing the controller does notcure his victims; they either die immediately afterwards or continue doing the dead villain's bidding.
In Dan Abnett's Sabbat Martyr, Pater Sin's child psykers have the ability to turn soldiers of the Imperium against their comrades. Only a single individual manages to throw it off through an oddly straight version of the Power of Friendship, as his friends and comrades care too much about him to allow him to be swayed. In an interesting variety, the bad guys realize this and decide to just skip over that guy completely.
And in Sandy Mitchell's Cain's Last Stand, Warmaster Varan has the psychic ability to corrupt anyone he speaks with into his service. Even Adeptus Sororitas, a loyal and likable governor, and a Commissar-in-training, all of whom were portrayed as innocent victims but remembered forever in history as foul traitors. On the other hand, the commissar-in-training, broken free by Jurgen's blank ability, managed kill himself before he succumbed again, and Cain fulfills his last request.
It's also used liberally in the background by both the powers of chaos (dominating psy powers) and the Imperium's Ecclesiarchy - the latter using a combination of mind control, lobotomy, combat drugs and cybernetic implants to turn heretics into arco-flagellants, Ax-Crazy combat monsters sent into battle against other enemies.
Happens in the 2nd and 3rd Mistborn books. Emphasis on "crazy".
The Imperius Curse in Harry Potter, one of the three Unforgivable Curses and essentially the magical equivalent of your average mind control device. Bartimus Crouch, Jr. (alias Professor Moody) was quite fond of it.
The House Of The Scorpion: Takes place 100 years into the future, where clones are raised to provide organs for a corrupt drug lord and victims trying to cross the border to the United States or Aztlan are forced to become opium-picking zombies programmed by computer chips in their heads.
Early in The Legacy, Wulfgar is convinced that his fiancée, Catti-Brie, has been cheating on him with Drizzt, so he goes and tries to kill Drizzt. Later in the book, it's revealed that he was hypnotized into thinking this and into feeling homicidally angry about it.
The Mirrorworld Series: Will, who nearly kills his own brother after smashing through a wall while unable to recognize him.
Happens to George in a Nancy Drew book, though she doesn't harm anyone, just spends the book bed-ridden and terrified and constantly begging Nancy to drop the case, lest harm come to her.
In Smallville, Delete, Clark, Lana, Martha and Jonathan are brainwashed into attempting to murder Chloe violently.
Ace Lightning gets one of these in episode thirteen of his first series complete with dreary monotone voice. He was snapped out of it by a data transfer, because you know, he's a video game character, they can do that.
In season 7 of Buffy the Vampire Slayer Spike is brainwashed by the First Evil to start killing again whenever he hears the tune "Early One Morning."
In Season 8 this happens to Angel, who kills Giles under the control of Twilight.
Several of Arthur's knights later suffer this at the hands of Lamia.
In season 5, Gwen falls prey to this at the hands of Morgana.
Doctor Who featured Jo Grant on her first appearance ("Terror of the Autons") getting brainwashed by the Master and sent to open a box at UNIT HQ — which contained a bomb. The Doctor specifically defines it as this trope, saying that an ordinary hypnotist couldn't force anyone to do something they didn't want to do. Yet The Master can manipulate people any way he likes.
The series contains numerous other examples; the instance in "The Masque of Mandragora" is interesting, as Sarah Jane, in her altered state of mind, becomes after thirteen years the first companion to notice the oddity of everyone in the universe speaking English.
In the Stargate SG-1 episode "Family" (2x08), Rya'c is brainwashed in this way by Apophis.
In the later episode "Enemies" (5x01), Teal'c, Rya'c's father, has the same thing happen, again inflicted by Apophis.
A whole episode is devoted to making Teal'c rethink his life and fight through the brainwashing. Initially, he manages to convince everyone on the base that he's been cured... until his mentor Bra'tac looks into his eyes.
Za'tarcs are another form of brainwashing.
This this case, the subject becomes a Manchurian Agent, acting normally until triggered by a specific event.
Adria tries to do this to Daniel, but the remnant of Merlin in him protects Daniel from her powers, although he convinces Adria that she succeeded.
Used in several episodes of Hawaii Five-O. One episode explicitly made the "can't do something they wouldn't do otherwise" statement, but then showed a theoretical way around it when, as a demonstration, one character was hypnotized to "shoot" another (with an unloaded weapon) by the hypnotist telling him the person was a double who was about to start a nuclear war and shooting him was the only way to stop it. Other episodes, however, including the Pilot Movie, used the standard fictional "make 'em do anything" portrayals.
Easily half of Power Rangers' main characters have had this happen to them at least once. Tommy Oliver, the first Green Ranger, had it happen three times. (In fact, that's how his whole career as a Ranger started.) Brainwashing tends to be magic-based, not hypnotic, in this show, and numerous characters have had "spells" make them act a certain way until the monster-of-the-week who placed it on them has been destroyed. Sometimes the Monster of the Weekis a character who was forcibly transformed and brainwashed and crazy all at once.
And by extension Super Sentai. You can watch most of them on YouTube if you type in the heroines names.
Astronema from Power Rangers in Space was always the Super-Powered Evil Side of Karone, but only fit this Trope for the second half (roughly) of the series. Originally, she simply had amnesia and didn't know who she was. When she remembered, she honestly tried to make a Heel-Face Turn, but the Dark Specter had other plans, and used brainwashing to keep her under his control until she was ultimately saved in the Season Finale.
In an episode of Lois and Clark, Lois is one of a group in a medical facility who are brainwashed into being contract killers before being killed their selves by the doctor at the facility.
In the Magnum, P.I. episode "Did You See the Sunrise" it turns out that Magnum's friend TC was brainwashed to become a sleeper assassin by Russian agents while he was a P.O.W. of the North Vietnamese.
In the episode "Night School" of Teen Wolf, Scott is by an Alpha Peter Hale. He snaps out of it pretty quickly, but still...
Jackson as the Kanima. Can be snapped out of it when people he cares about are in danger to be hurt by him.
One episode of The Equalizer features an experimental setup in which sidekick Mickey's memories of McCall saving his life are switched out for a scenario of cruel betrayal, thus giving him the motivation to assassinate McCall. And it still doesn't work, since it turns out that Mickey's loyalty is still strong enough for him to realise what's happened.
The main antagonist of LOST, The Man in Black infects certain people with a sickness which turns them into crazy psychopaths. Known victims of The Sickness are Claire, Sayid and most of Rousseau's science team.
In Chinese Paladin, this happens to Ah Nu near the end of the series, due to making a Deal with the Devil to save her lover Tang Yu. She unknowingly kills her own father in this state.
Angel has Jasmine brainwashing the entire town of L.A. into becoming her servants. When Fred, later Angel, and then the rest of the team are freed from her control, she proceeds to send all her possessed minions after them.
The newer series of Mission Impossible had a psychiatrist at his facility 'hypnotizing' select patients , with a combo of drugs and bio-microchips, then sending them out as hitmen. He gets ahold of undercover Nick.
In Helix,The Virus NARVIK-B has incredibly "focused behavioral patterns" that cause its victims to behave in this way, as they are compelled to spread the contagion. Though violent and paranoid, Vectors are also cognizant enough to form plans to access uninfected, like Patient Zero Peter Farragut, who manages to find a workaround for a biometric lock via Borrowed Biometric Bypass, severing the arm of a security tech at the research base where he works.
In Infinity Game, the previous DM caused all the NPCs to go completely insane and kill everybody, though they were somewhat aware of what was happening as Trishia's sisters beg her to kill them or else they'll kill her first.
Exalted: Most Exalted have a Presence charm that allows them to give other characters compulsions. If your character is an Abyssal, the result will probably be this trope.
Various RPGs have various powers used to control or influence others, such as the Dungeons & Dragons spell suggestion, and the charm and dominate series of spells.
At least in the third edition, Charm explicitly didn't work like this, despite being used as such in every game. It only makes the victim think of the caster as a friend, but it doesn't let them forget their other loyalties, meaning they'll likely be rather confused and anguished when their friends attack each other.
Dominate also cannot make a person do anything directly self-destructive ("stab yourself with your sword", "jump off the castle wall"), and if a dominated person is ordered to do something that is against their nature, they receive a new saving throw, with a cumulative +2 bonus. (A good demonstration is found in The Order of the Stick when they attempt to break the spell on a dominated paladin by disguising Belkar as lord Shojo, said paladin's master and lord.)
Order of the Stick also provides a good example of how Charm works, again with Belkar. He refuses to kill his friends and give their magic items to Nale... but since he's Chaotic Evil and a greedy bastard, he has no trouble killing them while singing the complete score to Meet Me In Saint Louis as long as he can keep their stuff.
It's hinted that this was Sergeant Kelly's fate in Doom 3. Before you were sent to Hell, Kelly gave you the mission to use a card with a plead for reinforcement to Mars. After either you send the message or not, Kelly orders you to get yourself to the Delta Labs and meet him there, so that both he and you can take care of the portal. When you're there, he's nowhere to be seen and you have to take care of the portal yourself. Once you came back from Hell, you no longer have radio contact with him, and later, you find out that Kelly had become a monster named Sabaoth. Whether he was allied with the demons in the first place or was simply brainwashed is unknown, but it should be the latter, since he seemed bent on defeating the demons, and Dr. Betruger was shown to transform marines into elite demons.
Original Generation Gaiden adds more people in this trope: Shouko, Lamia and Fernando (Though Fernando has actually fallen into this trope since his debut in Compact 3)
Happens to Touma in Super Robot Wars Alpha 3, though it's not like he's subjected into brainwashing by the enemy. Using his mecha's system too much caused him to gain an Ax-Crazy version of Mind-Control Eyes, and he went really berserk as if the system brainwashes him... all because he's pumped with too much hot blood essences.
And apparently, the first Banpresto Original to receive this treatment was Tytti Noorbuck in Super Robot Wars Gaiden. No, Shu, with all your Marty Stu -ness, you don't count.
Also happens to Brooklyn Luckfield (aka: Bullet) in Alpha 2.
In the Virtua Fighter anime and games, Sarah Bryant is kidnapped and brainwashed by the Judgment 6 organization into attacking her brother Jacky and (in the anime) their friends Pai and Akira.
In the last chapter of Fire Emblem: Genealogy of Holy War, Archbishop Malfoy kidnaps Julia and brainwashes her to attack your army. Since Julia is necessary for defeating the final boss, you must carefully distract her without killing her while sending the rest of your army to assassinate Malfoy and free her.
Making this even worse is that Manfloy did the same to Julia, Julius and Seliph's mother, Deirdre, to make her marry Julia and Julius' dad Alvis. In her case, she stayed brainwashed for years, only sort of breaking through when Julius fatally struck her down.
Also, in the Jugdral games there is a Sword that has the same effect as the Berserk Staff, but doesn't cause the insanity as much, and often times is pointless— enemies with or hit by the sword are still at range 1 when the effect kicks in, often attacking the sword wielder again.
In The World Ends with You, multiple characters are brainwashed into attacking the main character; some of them, admittedly, already had done that once, but this time it was against their will. To list a few: Shiki, Uzuki, and Kariya.
Metal Slug 6 has one mini boss fight where you have to fight one of the other playable characters who is brainwashed by aliens.
In Vanguard Bandits, this is the special power of the Zulwarn ATAC. Falkner uses it in three of the endings: in the main "good" ending, he uses it on several of the minor heroes, forcing the heroes to sacrifice their friends for freedom; in the main "bad" ending, he hits Bastion with it, forcing him to attack his allies; and in the Cecelia ending, he attempts to use it on Cecelia as punishment for her Heel-Face Turn = which torques off Bastion and causes his ATAC, Ultragunner, to blast Falkner with a counterattack.
Final Fantasy Tactics A2 does this for Adelle in one of the late story missions and Luso has to talk to her several times in battle to help her regain her senses.
Early on in Tales of the Abyss, Guy gets stuck with a Curse Slot that allows the bad guys to control his actions. Later on they activate it, causing Guy to get Mind-Control Eyes and attack Luke. However, this is revealed to be a subversion of this trope's usual modus operandi: the Curse Slot cannot control a person's actions; rather it manipulates the person by stirring up certain memories. Long story short, Guy would never have attacked Luke unless, at some point in time, he wanted to kill Luke.
Three characters in Final Fantasy IV qualify. Kain becomes mind-controlled by the villain Golbez. Although he later breaks free of Golbez' control and joins the party, still later in the game Golbez again takes control of him. This leads to Kain breaking free yet again at the time that Golbez is revealed to have been mind-controlled all along by the game's real villain, Zemus. Also, though a case of mind control, at one point in the game Yang winds up with amnesia and is recruited into Baron's guards. Being defeated by the party cures him.
Unlike other examples, the way Kain and Golbez were mind-controlled actually relied on their internal weaknesses. Golbez exploited Kain's jealousy, which led to his brainwashing, while Golbez's weakness was his own self-loathing, which was how Zemus brainwashed him. Also unlike other examples, they also feel regret because it WAS their own weaknesses that led to their mind control.
Cloud Strife of Final Fantasy VII, at the point in the game that the party has acquired the Black Materia needed to summon Meteor (Doomsday Spell), gets his mind broken by Sephiroth. Not only does he hand the Black Materia over to the original One-Winged Angel, he beats the tar out of Aerith, the one person who could stop Meteor once it was summoned.
Though he first had to be mentally manipulated and broken before he could be directly controlled. Also, it was more like Hypnosis since it Cloud's Weak Will that allowed him to be controlled like this in the first place.
This happens again later on when Cloud nearly kills Aerith himself, only to snap himself out of it at the last second.
World of Warcraft has been big on this ever since the Wrath of the Lich King expansion, filling much of Northrend with mysterious whispers in certain locations; turns out the uniting element is the Saronite Ore being mined in all these locations provides a direct link to its creator, the Old God Yogg-Saron. He's managed to Mind Screw everyone from newly-arrived homesteaders from the rest of Azeroth all the way up to his own Titan-appointed jail keepers through his years-long mental barrages.
This is a major fight mechanic in the Yogg-Saron encounter. You start with a sanity meter at 100, depleting when you suffer from Yogg-Saron's various maddening abilities or stare directly at the laughing skulls within the hallucinations inside his mind. If it goes to zero or you remain trapped inside his head when the hallucination sequences end, you go mad for the remainder of the battle, attacking your allies. The players who suffer from this even perceive their allies as faceless horrors while Yogg-Saron whispers his insane drivel to them! This insanity persists even if they die and get resurrection during the fight by their allies, only destroying Yogg-Saron or a complete raid wipe removes this madness.
The Sha in Mists of Pandaria use this heavily. They feed on and exploit specific dark emotions, allowing them to drive a mortal mad and eventually controlling their actions through the emotion. The Sha of Fear was perhaps the most successful, managing to take control of nearly the entire Mantid swarm.
Disgaea 2: Cursed Memories: The sad thing about Shura and Serion is that the seal placed on them by Imposter Zenon caused them to forget the very promise they made to their son, Adell - the long-reaching psychological damage that caused him to be lifebound to every promise he makes, as well as the denial about his demon heritage. The few moments of lucidity they get to enjoy from then on out are used to help Adell carry on where they failed and ask for a Mercy Kill; otherwise they are completely bound to their new master's whims. To this day Adell still does not know that they are his parents; whether or not the others do is up to NIS to decide, but if the truth ever comes out, it won't be pretty.
Happens again in the sequel, Marvel: Ultimate Alliance 2, only done by the Fold instead. Seems like the programmers like forcing you to beat the crap out of everyone in the game, regardless of whether they're on your side.
In Crash Nitro Kart, N. Trance brainwashes Polar, Pura and Dingodile to form a race team to put against the Bandicoot.
In Crash Of The Titans, Coco is brainwashed to work on the Doominator (thus trying to wipe out Wumpa Island...and kill Crash).
In Crash Mind Over Mutant, Crunch, Coco, and a lot of mutants are brainwashed with the NVs to turn evil...and try to kill Crash.
Let's do some Maths; not counting the mutants, there have been TEN cases of brainwashing, SIX individuals involved, across FIVE games, with TWO of the individuals being brainwashed and crazy THREE times. This does not take into consideration all the mutants in the lattermost game, which could make the individuals and cases into the hundreds or thousands. Oh, and we haven't even mentioned the whole deal with the Cortex Vortex and Cortex Commandos. If Code Geass is "Brainwashed: the Series", Crash Bandicoot is easily "Brainwashed and Crazy: the Series"
In the "Rebirth" expansion for First Encounter Assault Recon this trope is applied to the Player Character. You end up losing contact with your squad and fightign ghosts, only to find that the "ghosts" were your squad, who're now trying to cure the crazy the only way they know how (i.e. euthanasia). The rest fof the game consists of fighting past them so you can become the new Paxton Fettal.
In BioShock, Jack is programmed to find and kill his biological father. Is justified in that Atlas has manipulated him so well that his suggestions come across as reasonable, to the character and the player.
Spend enough time in the presence of a Reaper in Mass Effect and you will succumb to its will permanently. More horribly, it's implied that you are fully conscious of the effect, but can't do a thing about it. This is also known as "a sour note from space", with which Sovereign compelled the ancient rachni into fighting a Bug War until they became (almost) extinct.
Don't think of Reaper indoctrination as mind control; think of it as someone forcefully destroying your free will. The worst part is that Reapers usually have it happen slowly: most of the time, their victim doesn't even realize they're being manipulated, and think that these thoughts, which just happen to help the Reapers, are their own and are perfectly reasonable.
The Leviathan has a similar ability: the difference is that the Leviathan's mind control isn't permanent (it only lasts as long as the Leviathan is directly thinking about it), and it doesn't necessarily destroy a person's mental faculties (although it certainly can). Since the Reapers were built in the image of the Leviathans, their indoctrination is a more advanced and developed form of the Leviathan's control.
Jack, aka Subject Zero, is a more direct version of this Trope in Mass Effect 2. She was injected with drugs as a kid to equate killing with pleasure.
In a strange twist, you can get this ability. If you side with Morinth, you can learn her loyalty ability, Dominate. It stuns enemies, gives them a biotic shield, and makes them attack their allies for a few seconds before they come to their senses. Essentially, it's AI hacking, but for organic opponents.
In Mass Effect 3, it's revealed that Cerberus troops are Indoctrinated and have been implanted with Reaper technology, making them appear semi-Huskified. The Illusive Man has also fallen under the spell of Indoctrination, which you can make him realise at the end of the game.
Somewhat subverted with Kai Leng. Despite being heavily Indoctrinated, it hasn't appeared to have altered hispersonalitywhatsoever.
The pyramid in Stationfallslowly turns all machinery, intelligent or not, against their creators. And that includes your Robot Buddy, Floyd.
In the Spyro the Dragon reboot, Cynder is the unfortunate victim of this by The Dark Master. He had her kidnapped and brainwashed her into his loyal and powerful (and also surprisingly literal) Dragon. Spyro finally beats her and returns her to her normal self, but she's so guilty over what she did, it haunts her most of the series. Then in the Grand Finale, Malefor uses a Hanibal Lecture to confuse her enough for him to brainwash her again to turn her against Spyro. Thankfully, she's saved this time by the Power of Love.
Venus, from the non-canonical Metal Gear Acid 2, attempts to kill Snake 2.0 after recovering the Lucindia File because Wiseman ordered her to, and it is heavily implied, if not outright stated, that Wiseman removed her free will when creating her, meaning she really did not have any other choice but to comply.
In Metal Gear Solid: Portable Ops, there is Null, the Perfect Soldier: He used to be a war orphan named Frank Jaeger, but he ended up taken by CIA agents from a relief center as a test subject. As he was the only surviving and successful test subject, Null had no emotions, doubts or even memories, and presumably no free will, as he had only one purpose: to complete the mission.
Bonus Boss Ancient Devil in Golden Sun: Dark Dawn will sometimes take control of one of your party members and force him or her to fight by his side, making them an enemy. What's worse is that they can use everything they have against you, including weapon unleashes, items, Pysnergy, and using your own summons against you should you have any Djinn on standby. This gets a whole lot worse if the manipulated character has powerful healing abilities or uses the all HP restoring Potion on the boss.
In the main game itself, we have King Volcheck as the Chaos Hound.
In Call of Duty: Black Ops, it is revealed that the player character, while interned in a labor camp, was mentally conditioned to seek out and kill the President of The United States when read a certain string of numbers. However, his unusual degree of willpower allowed him to resist... whereupon he was brainwashed into channeling the dying wishes of a Russian prisoner. Futhermore, he's one of hundreds of sleeper agents scattered across the United States, all of whom have similar programming. The icing on the cake is when, in the ending cutscene, it's implied that despite killing the man who imprisoned and hypnotised him, the player did end up succumbing to the conditioning and carrying out the assassination.
Eternity swords can be very difficult to handle properly in Eien no Aselia. As evidence, Kyouko's mind is devoured by Void almost as soon as she gets it and at the end of the game the Shun that Yuuto once knew is dead, similarly devoured by The World.
Averted, however, with Cloud, who is simply doing his job, until Sephiroth attacks Tifa in an attempt to get Cloud to fight him. He defects in time for the last cycle.
Strictly speaking, the Zerg in the original Starcraft are this, as the Xel'Naga instilled them with an overriding biological imperative to absorb the genetic potential of other species into their own, whereas they were previously peaceful and harmless worms low on the food chain of their homeworld — no, this isn't a spoiler, it's All There in the Manual. Starcraft II reveals that the Overmind actually orchestrated his own death and groomed Kerrigan as his successor in order to finally grant the Zerg true free will, as she was not hampered by the same imperative.
Happens by accident in Drakensang: the Dragon Carbuncle you give to the Dwarf King Arombolosch turns out to be infested by a Demon, which eventually takes over the dwarf king, forcing you to defeat him in battle.
Sword of the Stars II reveals that the Screamers are actually Morrigi who were turned against their own by Suul'ka.
Kerrigan in Starcraft, for she was forcibly infested and transformed into a slave of Overminds against her will.
The whole deal with Bison's Bodyguard Babes the Dolls relays on a group of teenage girls from all over the world being kidnapped and subjected to this treatment to end up as an Amazon Brigade. Only when one of them (Cammy, Bison's Opposite-Sex Clone) starts breaking through, and the survival instincts of two Dolls (Juni and Juli) prove to be stronger than the brainwashing, the whole plan begins to crumble down. However, it takes much more than mere defusing to get them back to something similar to normalcy, as in the Street Fighter IV Juri OVA we see that the girls must receive extensive medical treatment in Shadaloo capsules. Later, T. Hawk and Cammy's paths reveal that Juli has become an Empty ShellEmotionless Girl and Juni is amnesiac in a British hospital; while it's not certain that the first will ever get better, the second is in her path to a slow but sure recovery.
Midway through Alpha 3, several story paths intersect thanks to this trope. Ryu is captured by Bison to become his "host body", then is infused forcibly with the Psycho Drive's energy and ends up like this. Sagat is horrified when he finds out, has a Heel Realization and tries to snap Ryu out of his state; meanwhile, Ryu's friends Ken and Sakura fight Bison off. It takes both Sagat's prodding and Sakura being seriously injured by Bison to fully get Ryu defused.
To a smaller degree, there's also Ken being caught and brainwashed by Bison in Ryu's path, in a Shout-Out to the animated movie.
This is the reason why Kyo's father Saisyu is seen as The Dragon to Rugal Berstein in The King of Fighters 95. You have to fight and defeat to get him out of such a state.
In the Tales of Ash saga, this happens to both Chizuru Kagura in 2003 and Rugal's daughter Rose in XI. More exactly, both are controlled as a sort of People Puppets by Botan from Those of the Past. Chizuru is recovers almost at the end of 2003, right before the fight against Mukai; Rose remains like this and is freed only at the end of XIII.
Mother 3 combines this with Cybernetics Eat Your Soul for a truly tear-jerking example: Lucas's twin brother, Claus, goes missing early on in the game after leaving to avenge the death of their mother. Three years later, while Lucas is on his journey to save the world, they encounter a masked man on multiple occasions. This man is completely subject to Porky's control, commands the army of Pigmasks, and has the ability to pull the Seven Needles just like Lucas can. After six of them are pulled, Lucas and the Masked Man confront each other in front of the seventh. The Masked Man is revealed to be none other than a thoroughly brainwashed Claus.
A strange example in Star Wars Knights Of The Old Republic and Star Wars: The Old Republic. It's revealed in Revan, the prequel novel to the latter that the real reason that Revan and Malak originally fell to the Dark Side was the result of torture and mind-control at the hands of the Sith Emperor, being sent back as vanguards for the Sith Empire's invasion, but with no memory of the event. In Revan's case, this ironically ended up being broken when the Jedi also tried to brainwash him, causing the latter brainwashing not to entirely stick.
In the Foundry Flashpoint for Star Wars: The Old Republic, Revan is (possibly) implied to have undergone this again in the three centuries they've been held in stasis and tortured by the Emperor. His plan was to use the Foundry to create an army of Droids that will wipe out all those with Sith DNA, accounting for 98% of the Sith Empire (and a large amount of individuals in the Republic as well). It's left vague whether Revan's Kill 'em All plan is due to Sanity Slippage or if he might not be entirely correct about resisting the Emperor's control.
This happens to the Romulan player character in Star Trek Online, who due to bad luck with an Iconian portal ends up falling into the Tal Shiar's hands and ends up a test-subject for brainwashing into a loyal agent. Fortunately, you get broken out of it before they do any real damage — a deep-cover agent of the Republic manipulates the intricacies of what the brainwashing does to trick you into letting him un-brainwash you while you're still in the 'testing out how well the brainwashing took' stage of the process, and while you did some seriously bad stuff, they were bad stuff that would have happened (and just as easily) anyway — the only reason why you specifically is tapped to help put together a Thalaron weapon and implant Borg devices into a captive until she becomes a drone is to test how well the brainwashing took.
Everyone (or at least, all of Bowser's troops and all the native wildlife) in Mario & Luigi: Bowser's Inside Story. Fawful managed to hypnotise or mind control just about everyone in sight to worship him as some of celebrity/deity cross before physically altering their appearances to look exactly like himself, with the same creepy Slasher Smile and green colouring. You can even save the Chain Chomps from this fate by vacuuming away the parasites controlling them.
In the Order of the Stick. Nale, the Evil Twin brother of the bard Elan, casts Charm Person on the party's halfling ranger, Belkar Bitterleaf. The first attempt ("If you see any of your allies before I get back, kill them and bring me their magic items") fails because the spell won't allow the command to go against the character's basic nature, but the second ("If you see any of your allies before I get back, kill them and keep their magic items for yourself") succeeds, even when Nale adds, "While singing the complete score to Meet Me in St. Louis." Hilarity Ensues, of the actually hilarious variety.
Homestuck: One of Vriska's more impressive displays of her Mind Control abilities is an example of this. She controls Sollux and forces him into a Superpower Meltdown, and then uses the resulting Eye Beam explosion to kill Aradia. She later pulls off a fairly impressive "double psychic reacharound" to control Tavros and his Beast Master skills to in turn mind control Terezi's lusus and permanently blind Terezi. However, Vriska soon finds her powers are far less useful on humans; the best she can do is make a human fall asleep instantly ( Jade's chronic narcolepsy was in fact Vriska testing the limits of her powers on humans).
The Condesce later takes this Up to Eleven: Because she possesses the combined abilities of all the trolls, including the aforementioned powers of Vriska and Tavros, she is able to give Dogtier Jade a Grimdark form. She immediately commands Grimbark Jade to zap the Tiaratop onto Jane's head, converting her to the Borg-like Crockerdark form.
In MS Paint Masterpieces, Wily snuck in virus type programming into all the original robot master's to get them to defect. The POV comics with Cut Man's desperate struggles to remain himself are... disturbing and heartbreaking. Then you have the likes of Ice Man jumping headfirst into it and helping to spread the Mind Control.
Also, anyone under Quintet's Mind Control or using one of his support units.
Subverted in Exiern: Niels is attacked by a magic user and controlled to steal Peonie, then it's revealed that the spell is just controlling his body and while he can still talk and think, he's powerless to stop it, he apologizes, and then says that he can't do anything about it, so he's gonna have fun playing a bad guy.
Any and all dark Creturians who attack the protagonists in the web fiction serial Dimension Heroes.
In The Gamers Alliance, Jessica ends up brainwashed by the Clergy of Mardük and is sent to steal a magic sword from her friend Refan and kill Refan in order to leave no witnesses. Kaizoku and Tanya also end up brainwashed by the same clergy although Kaizoku eventually breaks free from the clergy's control.
In one episode of Captain N: The Game Master, Eggplant Wizard and King Hippo brainwash Simon Belmont with a literal brainwashing machine (complete with detergent), changing him from Vampire Hunter to N-Team Hunter.
Transformers: Beast Wars saw Megatron inflict this trope on Rhinox, who became so evil Megatron was forced to change him back. Apparently learning his lesson, in Beast Machines he completely changes the personalities of Silverbolt and Rhinox when he puts them in Vehicon bodies. So much so, in fact, that the Maximals don't recognize them until Rattrap hacks into Rhinox's memory banks. This time, unfortunately, Rhinox does not become good again once his memories resurface.
Teen Titans: Brother Blood brainwashed the Teen Titans East (Aqualad, Mas and Menos, Speedy and Bumblebee), and he plans on using them to destroy Cyborg and/or turn them into his new H.I.V.E. academy students. It was so well-done that they used to provide the picture above.
In Batman Beyond: Return of the Joker, Joker and Harley Quinn brainwashed Robin/Tim Drake in into essentially becoming another Joker. However, this ended up backfiring when Tim broke through the brainwashing when ordered to kill Batman and instead killed the Joker.
In Jimmy Neutron's "One of Us", an alien disguised as a kindly old lady uses televized mass hypnotism to turn all the citizens, including Jimmy's parents, into happy, mindless meat puppets forcing others to join the fold.
In The Fairly Oddparents episode "Moooving Day", Timmy is forced to move into a neighborhood where everyone, including his friends and family, act the same. It's revealed that the milk that comes with the new homes turns anyone who drinks it into a Stepford Smiler obsessed with milk, including his parents and godparents, who try to persuade Timmy into becoming like them. All orchestrated by wealthy businessman Doug Dimmadome to earn more cash.
Inspector Gadget: Gadget was once hypnotized by Claw's lackeys into robbing a bank, once again forcing Penny and Brain to clean up his mess.
Justice League: Ancient sorceress Morgaine le Fey partially brainwashes Martian Manhunter to steal the powerful Philosophers Stone with promises of reuniting with his home and dead family. He almost hands her the stone, but the memories of Etrigan the Demon (who was one of her earlier victims), finally allows him to break control of the spell and shatter the stone, noting that the price would be too high.
Samurai Jack: As Jack passes through a town, he discovers that all the children of the town are going to a rave party and have been hypnotized by Aku's music played by an evil DJ, which is being played on the outskirts of town, turning the children violent and keeping them away from their parents. In addition, with or without the brainwashing, the children are dressed in what seems to be a "candy raver" style.
Justice League Unlimited: In "Grudge Match", minor villainess Roulette uses Gorilla Grodd's mind control technology to "recruit" female heroes into fighting in gladiatorial combat games to fund Lex Luthor's machinations for reuniting with Brainiac. BC and Huntress have their work cut out for them trying to get the mind control devices off of their teammates, but once they do, the real fun begins as Roulette reveals the next contestant: Wonder Woman. It's all the four women can do to keep their heads attached as the League's number one warrior barrels into them like a female god of war. By the time Huntress and Black Canary shut down the mind control signal, Wonder Woman was a split second from smashing Vixen and Hawkgirls' skulls together.
In the Jonny Quest: The Real Adventures episode "Thoughtscape," Jessie is brainwashed by Jeremiah Surd via Questworld, so that she will destroy her family, or at least be the bait to bring Race Bannon to Questworld so Surd can kill him directly. It almost worked, too: She destroyed half the Quest Compound!
In one Adventure Time episode, the Fight King brainwashes Finn and commands him to kill Jake. It's later revealed that Finn was faking it as part of a plan.
And again in the episode "Chocolate Chips", where a mad chocolatier uses Mind Control drugs to turn the rest of the Rangers against Dale, reversing the previous scenario.
My Little Pony: Friendship Is Magic example: Word of God re: Nightmare Moon is that Princess Luna was jealous of how all the ponies pranced and played in her sister's bright daytime but slept her beautiful night away, but she kind of kept it to herself and tried to carry on as usual. But a dark force saw that jealousy and used it to invade her consciousness and wreak havoc as Nightmare Moon; when the mane six hit her with the Elements of Harmony it was driven out and all that was left was a remorseful Princess Luna. This dark force hasn't been seen or mentioned since.
The Nightmare Forces do return in the Expanded Universecomic, where they exploit Rarity's fears to turn her into the next Nightmare. Luna and the rest of the mane cast help her to defeat the Nightmare Forces on the Moon.
In Young Justice this happens to the entire Justice League in the season 1 finale. The Team assumes its brainwashing initially, until its revealed to be more like a puppet-master controlling them; giving an advantage to the heroes, because the mind-controlled have to wait for instructions to do anything.
A more traditional case would be Red Arrow who had specific subconscious commands plugged in. The same fate would have awaited Superboy if he hadn't been rescued in the first episode.