A dangerous villain or a brutal Anti-Hero, either a teenager or an adult, with a childlike nature, which creates a dissonance between innocence and savagery. Such characters can become repositories for Nightmare Fuel, especially if their childishness is never explained. Contrary to the term, many examples are not necessarily psychopaths in the clinical sense. Misaimed Fandom may not be out of the question, either; sometimes the character's more "Moe" attributes will be picked up on and subjected to Flanderization.
The exact extent of the character's childishness will vary, and in general Psychopathic Manchildren can come in several varieties, with possible overlap. Such a character may:
Seem superficially powerful and cruel, but have very childish or simplistic goals or motivations. May overlap with One of the Kids—if the cruelty part isn't played up to horrifying levels.
Actually possess a lot of power, intelligence, and/or prestige, but also have some childish qualities or behaviors, to fit in with a certain aspect of the story being told, or else advertise that there is something seriously wrong with him/her, to make him/her creepier. These are most likely to be a story's Big Bad.
Be subject to a personal variation of Values Dissonance where violent, savage actions are viewed by the character in question in the same light as regular play is viewed by most real children. This variant is often an especially strong source of Nightmare Fuel due to the uncanny dissonance between his/her childish demeanor and the viciousness of his/her actions.
Be completely or largely inexplicable, and the discrepancy between the different parts of their personality Played for Laughs.
Johan Liebert of Monster is a classic example. His goals and desires are highly simplistic but as an adult he pursues them with an appropriate level of sophistication. Exactly how childish he really is can be hard to judge given that he's an excellent manipulator.
Miata is little more than a child (who actually breastfeeds from Clarice to stay calm) though several other fighters don't realize this, what with her ungodly ability to kill masses of Yoma at a time. And, if necessary, with her bare hands.
Priscilla may count too, at least until she awakens.
Gluttony from Fullmetal Alchemist is a ridiculously strong Artificial Human with the temperament and intelligence of a young boy. Throughout most of the series, he's reliant on his "keeper" Lust to do the thinking for him (his main input being to ask her if he can eat people). When she dies, the poor guy suffers a nervous breakdown.
King Hamdo from Now and Then, Here and There is a power hungry ruler (with more than a passing resemblance to certain African dictators) who throws tantrums and calls for his assistant Abelia to comfort him when things go wrong. He thinks little of human life and often laughs maniacally.
Mao from Code Geass, whose child-like attitude is slightly justified by the fact that he was orphaned at a young age and never received anything even resembling a traditional upbringing. That does not justify the wanton More Than Mind Control he engages in...
However, this is horriblyflanderized in the fandom. In the canon strips, he says creepy things and stalks people from around corners, but has only actually done anything a handful of times, and none of it was sexual (except possibly the time he put Lithuania in a French maid outfit and whipped him while he was working). But many fans tend to take this trope Up to Eleven and make Russia a bratty, smug, rapist bastard without any good traits that would put Stalin to shame.
Dark Action Girl Nena Trinity from Gundam 00 is an excellent Type D. She's pretty, spoiled, cheerful, friendly, mock-fights with her brothers, will happily invade your personal space and kiss you if she thinks you're cute, has a really funny mascot in the form of her purple Haro... but after being raised as a Tykebomb Artificial Human with no concept of morality, she will bomb your house if she's got to work while you have fun at weddings. And then she'll be all "Whoopsie! :3" when asked why did she do that.
In the side materials, it's strongly implied that there's a pretty good reason for this: seventeen-year-old Nena was kept in stasis almost from birth... and only woke up around seven years before the series starts. As such, her mental psyche isn't the same age as her physical body. She's basically a little girl in the body of a teenager; such stuff does a LOT in the mental/emotional maturity of anyone.
Rosamia Badam from Zeta Gundam. She's a Type D as well, but in different terms: she's a 17-going-to-18 year old Dark Action Girl who, outside her mecha, has the mentality and the fears of a little girl, latches innocently on whoever she sees as a Replacement Goldfish for her dead older brother, and is borderline unable to take care of herself in a normal environment. In her case, it's very justified: Rosamia not only is a survivor of the infamous Zeon Colony Drop of the One Year War, which happened when she was a little girl, but was subjected to cruel experiments that messed up with her mind even more.
Gundam SEED has Muruta Azrael, a psychopathic genocidal maniac, motivated entirely by childhood grudges, and possessing the maturity level of a particularly vicious teenager.
Renge in the Flame of Recca manga, who is so childishly nuts she tore up a Teddy Bear just because it doesn't answer her when it doesn't have a speaking device, only to cheerfully laugh to ask for her Papa to get her a new one. Speaking of her Papa, Mori Kouran, she thinks her Papa's horrendous monstrous look after fusing with Tendou Jigoku looks EXTREMELY COOL. She doesn't end really well.
Bambi from Bambi and Her Pink Gun is incredible childish in many ways, but also subverts this in others. While she's a psychopath who acts almost entirely on instinct, she's also a vain health nut who doesn't eat anything she hasn't personally boiled and will kill you if you so much as smoke near her.
Fat Majin Buu from Dragon Ball Z is Type A - he has no idea that what he's doing is wrong, and is single-handedly converted to good by Hercule / Mr Satan. Super Buu is type C; he sounds increasingly intelligent once he starts absorbing people, but still throws tantrums when he's outmatched. Kid Buu, who doesn't have any desires that don't involve blowing things up, is Types C and E put together.
Broly is somewhere between Type B and Type C, arguably. His motivation to kill Goku? Goku's crying scared him when they were babies in the same 'nursery'.
Also Emperor Pilaf from Early Dragon Ball, and Dragon Ball GT.
Chilled from the Gainax manga Episode of Bardock presumably qualifies under this trope, as he has shown himself to be exceedingly childish, and yet was shown to be even more ruthless than even Frieza, notably killing one of his soldiers while in a good mood just because the soldier was unfortunate enough to just happen to be blocking his view.
Android #17 is Type B. Even more so (in fact a cross between B and E) in the Bad Future of Future Trunks' timeline, where his sister is one of these also to the point 'go on murderous rampage' is her default response to not getting what she wants. When Future Trunks shows up and she wants to kill him to blow off steam, #17 said 'ok, we can, but we'll miss out on weeks of fun playing with him', treating it more like a game than their nemesis. Trunks actually calls him out on it before killing him.
General Blue technically qualifies. Although he has other reasons for disliking Bulma, his exact reaction regarding Bulma's attempts at seducing him is extremely similar to a little kid not wanting to interact with the opposite gender due to a fear of cooties.
There's also Recoome of the Ginyu Force, though he might simply put on this air to taunt his opponents.
Even Frieza gets to have traits of this. Usually behaves in a manner similar to that of a spoiled child. The most notable example is when he comments in hell about Goku fighting with Kid Buu.
Light himself qualifies as Type C (flirting with D). When L details the psychology of Kira to the police, one of them suggests that they could stop him by no longer publishing the name of convicts in the news, as he clearly was getting the names of his victims from the media. L states that won't work because Kira will then simply start killing people he thinks are guilty and will further blame the police for any innocent people he kills, and L specifically identifies his childlike personality as the reason for this. Sure enough, Light does display lots of childlike evil throughout the series, such as killing the fake L for insulting him on national television and his need to gloat to L and Near when he thinks he's beaten them. His Villainous Breakdown at the end takes the form of a blatant childish fit.
Ryuk is type B-a cruel monster who sets everything off because he's bored.
Depending on how you interpret the series, you could probably include Beatrice, Eva-Beatrice, and Erika in this trope. All the witches except (maybe) Virgilia are prone to Immortal Immaturity, though in Lambdadelta's case her childish behaviour is just an act, and Beatrice is later revealed to be only 19 years old and not a thousand as she claims. Though when you take her upbringing as Yasu into account, you can't exactly blame her. Maria gets excused because, well, she is a little girl.
Wonderweiss Margela from Bleach fits pretty well. He can't even speak coherently, but heaven help you if you don't let him play with your hat or aren't Yamamoto. Technically he's a Type A - under Aizen's full control, appears to have limited understanding of his actions, will attack Aizen's opponents, but seemingly at random with no real indication he's enjoying the violence as such.
Arguably Kano from Texhnolyze. He's eloquent, intelligent and charismatic, but that doesn't change the fact that he sees the world as a one big playground, and himself as the only real person in it.
Diva from Blood+ is a very depraved type B. For example, in episode 24, she bites young Riku and drinks his blood, then childishly laughs and jumps around in a white and blue Pimped-Out Dress when caught by the heroes, before she captures Saya herself and almost kills her. Later, she will rape and kill Riku to impregnate herself.
Friend from 20th Century Boys is a rare Magnificent Bastard version of this. As clever as he is, it doesn't change the fact that he is only trying to destroy the world because he never grew out of his childhood grudges.
Machina of Hayate the Combat Butler. He nearly kills Hayate, even stating it wouldn't be murder, and later on he turns into a giant snake. He also Gets very excited when his master gives him money to get something to eat and orders 100 hamburgers all at once.
The main character's parents, with heavy emphasis on manchild.
Pegasus J. Crawford / Maximillion Pegasus from Yu-Gi-Oh!. He steals people's souls (including a small child's), tries to take over a company by killing the CEO and pursues Ancient Egyptian artifacts with no regard for anyone in his way, all to bring his wife Back from the Dead. In his spare time he watches cartoons and loves them to the point that he creates a DECK based around them. In the anime, he becomes a good guy later on, though. (Ether type C or type B)
Lucy from Elfen Lied is a mixture of types C, D (counting Nyu), and E.
The silpelits can also qualify even though they're chronologically children because they age quicker.
In One Piece, Monkey D. Luffy is your typical Shōnen childish Idiot Hero. So what happens when you remove his shadow and create a hundred-foot-tall monstrosity with it, using the body of an ancient demon warrior? Oars has all of Luffy's idiocy, childlike naivetie, and personality, with none of the tempering kindness and concern for friends.
Also in One Piece, the Demon Guards of Impel Down, four bizarre Zoan users seem more animal then man but like to goof on each other and cower whenever their officer Sadi-chan is angry like them like children to an angry mom. They are also extremely sadistic, and love the brutalize prisoners.
One of the newest members of the Blackbeard Pirates San Juan Wolf seems to apply. In his past, he was a Pirate who committed crimes "so atrocious they were effectively erased from history itself", a bounty likely to be in the upper multi-millions, and when caught offscreen, was transferred to the lowest level of Impel Down, and to earn his freedom from there, was forced to kill everyone in his cell on orders from Marshall D. Teach and co. Also, he is the largest man alive in the show, easily dwarfing Oars at least four time over, and is compared to a walking Sears Tower. But, in his first appearance, he peeks out from Maineford HQ's main building like a curious child, has an expression like he was caught stealing from a cookie jar when spotted by Mooks, expressed surprise that a Vice Admiral knew his name, and was scared by Whitebeard and hid while the rest killed him.
His classic "They found me!" line , which is all the more hilarious when one looks at this size comparison pic◊, yes the circled person is one of the regular giants.
Rip van Winkle from Hellsing is an excitable young woman who likes to sing opera beautifully and also enjoys killing things while laughing her ass off. She intends on conquering the world for Millennium.
Vincent Nightray from Pandora Hearts might as well be the king of this trope due to his nasty habit or slicing up dolls with scissors and causing the tragedy of Sabrie. There's also the Will of the Abyss, a whimsical and childlike being that rules over the hellish alternate reality of the Abyss. She veers wildly between moods, acting like an innocent little girl one moment and casually plucking a man's eye out the next moment. It's because she once shattered her own mind and memories to protect her sister and Oz, leaving her completely insane.
Jack Winslow of Power Stone is a really 100-year-old crazy who was orphaned at a young age and lost at sea. Lack of human contact might explain his behaviour.
Chrono Crusade has Joshua Christopher, who was kidnapped by the Big Bad as a young boy and given powers that turn him insane. Although he's 15 in the main bulk of the story, he still sometimes acts like the child he was when he was kidnapped, treating attacking a girl as a "game" and pouting about pudding being ruined right before slaughtering the demons responsible. The anime version emphasizes the "childlike" side, including the ending having him lose all of his memories and reverting back to the personality he had as a kid, while the manga makes him more mature and aware but possibly more insane.
The anime also seems to treat Shader this way, by keeping her Genki Girl personality but changing her morality from a grey shade to nearly completely black, giving her a sadistic streak to boot.
Puppetmon from Digimon, anyone? He kidnaps Takeru in order to play hide and seek. While trying to kill his brother Yamato and the rest of his friends, and then Takeru himself. Way to go.
Arguably Diablomon from Our War Games. There isn't much known about it, but consider that the e-mails it sends suggests that it sees the battle as a game, and that the only sound it makes (in the original version) is a creepychildish giggle.
Yukio Oikawa from 02 is a more sympathetic example, never really maturing after he discovered the Digital World and especially after his best friend died. He finally starts growing up after he meets the father and son of his late best friend again and realizes that they must miss him even more than he does. Sadly, it doesn't matter since he's been possessed by Myotismon.
Izaya of Durarara!!. One of the rare Manipulative Bastard versions. It becomes quite obvious as the series progresses that he sees everyone and everything around him as little more than toys to be played with until they break.
Eva-R and Eva-Q in Seikon No Qwaser are conscious of and delighted with being playthings, meant to suffer and die for Eva Silver. And yet in a backwards way, they regard any prospective dominant (i.e., anyone they look at) as their plaything, and are quick to break any 'toy' who isn't breaking them to their satisfaction.
Naruto has a mixture of villains who act mature and others who act like kids, though to be fair the same is true of the heroes.
Orochimaru definitely has elemenets of Type C with his gleeful sadism, particularly he resurrected the first two Hokages just to rub it in his old teacher's face.
The Type B Deidara is even worse and commits suicide just because Sasuke had beaten him and was treating him with indifference.
Sasori is a mix of B and C. He is an insanely talented and cold-blooded Puppetmaster in his 30's, who also transferred his essence into a puppet resembling his 15 year old self, and was more or less beaten by a memory of his parents coming to hug him. Justified Trope, though: Sasori's parents were killed in battle by Kakashi's father Sakumo when Sasori was a baby and he left the Sand Village when he was around 15 years old after killing and turning the 3rd Kazekage into one of his puppets. From his broken childhood to his subsequent defect from his village, he grew cold and stoic due to the lack of parental love, despite his grandmother Chiyo's efforts. His emotions were stunted to that of an abandoned, forgotten child, and his puppet body physically reflects the age he had when he left the place he was raised in.
Pain is a deliberate inversion however, as his villainy derives from a twisted version of Jiraiya's philosophy that growing up is based on suffering; since he has suffered so much, Pain believes that he has matured into godhood (in a non-Westernsense).
The anime portrays Hidan as a big Type B: he's the Akatsuki version of a Hot-Blooded, foul-mouthed, smartass rebel teenager in the body of a man in his 30's. And he'll kill whoever stands in his way bloodily and mercilessly.
Tobi aka Obito is a Type B. His goal is extremely childish: he wants to create a dreamworld where everyone can be happy and the good guys always win. The psychopathic part comes from the fact that he is willing to do anything to accomplish this.
Madara Uchiha, Type C: Incredibly powerful? Check. Head of his clan? Check. Co-founder of the Hidden Leaf, and, by extent, the entire shinobi village system? Check. So why does this trope apply? The entire over-arching plot is a temper-tantrum he throws after eavesdropping on Hashirama and Tobirama Senju, in their own home, and hearing Tobirama express his opinion that the title of Hokage should be voted on by the Village Elders and Clan Heads instead of just being handed to Madara because Hashirama wants him to have it. Ironically, Madara probably could have been voted Hokage if he didn't have a history of behaving this way.Also, he is extremely cocky.
He acts like a child with a new toy when it comes to the Juubi, as well as when he's fighting Eighth Gate!Gai. Heck, Obito calls him out on his behaviour with the former!
Ni Jianyi's pupil who is only known as Kami-sama in Saiyuki is a sadist who loves to toy with people while pleasantly torturing them (evident by "helping" Goku get rid of a pendant ball embedded in his leg). When the Sanzo group stormed his castle, he played games with them as if they were in an amusement park. They eventually found him in his room surrounded by stuffed animals which were actually the souls of people he had stolen. And once he started to lose, he threw a temper tantrum.
Tamaki, the Promoter of Deadman Wonderland. When he isn't causing the deaths of or torturing inmates he's often found playing with toys in his office, including a Lego model of the prison and a dancing flower. He's also a bit of an RPG Otaku and sees the Wretched Egg as a Big Bad to defeat.
There's also Mockingbird. He was by all accounts downright terrifying in battle and is one of the most powerful and feared Deadmen in the series this side of Wretched Egg, but outside of the ring, he was childish, playful, and didn't seem to take anything seriously except for his Morality Pet. Turned Up to Eleven when it comes to Hagire, who Body Surfed into him.
Kirika Kure of Puella Magi Oriko Magica is completely unfamiliar with the concept of maturity. Among other things, she throws tantrums at a moment's notice and drinks her tea with enough sugar to make it into syrup. She's also hunting down and killing other magical girls. Although her motive for doing so is because she was asked to by Oriko, whom she is obsessively in love with, rather than her childish tendencies. (Then again, killing others because Oriko tells her so could be seen as childish too, as she does so to please said person and get praise from them than of her own will.)
The Big O's Alex Rosewater. "This is my Big! This is my dome! You can't have it!" Also, to an extent, Alan Gabriel.
Amaimon of Blue Exorcist is a demon king who displays childish Cloudcuckoolander tendencies, uses his visits to the human realm mainly for sightseeing, and is extremely fond of candy. He's also excited by the thought of killing people and treats fighting like some sort of "fun" game.
Akihiko Kayaba of Sword Art Online trapped thousands of people in a virtual world of his one making with no way to log out other than to clear the game, walked among them as a player and rallied several of them around himself in one of its most powerful guilds, with full intention of betraying them as the games Final Boss, and made it so that anyone who died in the game was Killed Off for Real. In his final conversation with Kirito and Asuna, he reveals that he did this all so that the imaginary play world that he always dreamed of would be as real as he could possibly make it. He also seems to be oblivious to moral and ethical implications of his actions. To the point where the fact that he is responsible for the deaths of 4,000 people, is simply an abstract statistic to him.
Akura-Ou from Kamisama Kiss. One minute he is playful, happy and silly... the next minute he will brutally kill dozens of people for the most trivial of reasons.
Some fans of the Japanese version of Mewtwo from Pokémon: The First Movie have likened him to a scared, confused and angry child, placing him in types B and C of the trope. His motives amount to a psychic powered temper-tantrum (albeit one that is not entirely unjustified) as a result of his mistreatment and some of his dialog is childish in some aspects, saying "Don't tell me what to do!" when Ash and co. confront him on taking their Pokémon. The English dub averts this, glossing over most, if not all, of Mewtwo's childish mannerisms from the Japanese version.
Akito in Fruits Basket. He's essentially the same at age 19 as he was when he was little - a spoiled brat with a god complex and a crippling fear of abandonment. This is because she was horribly abused from before birth by her mother, who forcibly raised her as a boy due to petty jealousy and drilled in her mind the idea that nobody loved her, nobody respected her, and everyone would abandon her, which caused Akito to snap when she was in her early teens and become the Big Bad.
Arguably, Ren Sohma aka the aforementioned abusive mother of Akito. Not only her ultimate reason to abuse the Hell outta her daughter is ultimately very bratty ( being jealous because Akira, her late husband and Akito's father, loved the idea of being a dad), but at some point she tries to kill Akito... over a box that belonged to the dead Akira, simply because she believes everything Akira owned was hers..
The "Vampire" Clair Leonelli from Heat Guy J is a Mad Bomber who speaks very childishly (referring to his dead father as "Papa", for example), is prone to violent temper tantrums, and is described by one character as liking to "play with" his enemies before he kills them. He does have a Freudian Excuse, though, and his childishness is designed to make him seem fragile and sympathetic as much as it's used to make him frightening.
Dilandau Albatou of Escaflowne fame, the spiritual predecessor to Clair above, might be an even more obvious example, as when he's not fighting he spends much of his time throwing fits and having nervous breakdowns over things that range from understandable to entirelypetty. While Clair above shaded into both Type B and Type C, Dilandau is squarely in B territory.
It's a bit of a stretch, but technically you can call most of Batman's Rogues Gallery this. Two-Face, Riddler, Calendar Man, Scarecrow (kinda), Firefly, Maxie Zeus... seeing as how psychology-driven Batman is, it makes sense that all of his villains would be so simply motivated. Most of them are just trying to prove something to Bats, making them the "Childish Motivations" breed.
Specifically, TRY to deny that Joker's motivations are... arbitrary. You will fail in this.
The Joker is arguably one of the more fitting examples in the Batman Rogues Gallery. For starters, when Batman is telling Joker to stay away from the Gordons after he apparently hurt Gordon's wife (it was actually his son, Gordon Jr. who did the deed), Joker commented that he didn't do anything to "the old bitch", and starts commenting to Batman that he misses the old Batman, and commented that he "doesn't want to go to bed yet" and that he "wants to play."
The original Blockbuster was the type A. variety.
Humpty Dumpty, a minor villain, is something of a subversion. He's enormously obese and strong, and clearly insane—but not in a way that makes him want to harm anyone. Rather, Humpty is obsessed with making things "better" by taking them apart and putting them back together again, but because he doesn't have any of the skills necessary to do this correctly, he ends up causing destruction and a few deaths instead. However, he doesn't do this maliciously: he sincerely can't tell that what he's doing is wrong, and even helps Batgirl when she apprehends him by putting her dislocated arms back into her sockets, proving that he's not evil in any way. He's not in Arkham because he's a mass-murdering psychopath, he's in Arkham because he's actually crazy, and his doctors even view him as a model patient.
The Goddamn Batman could easily count as one, between his sadism and his petulance when people aren't impressed by his toys.
The Mad Hatter is probably the straightest example in all of comicbooks. His delusional obsession with a children's book and his kidnapping and murder tendencies come to mind.
And coming to Squee for a band-aide after cutting his hand on a "Skettie-Os" can probably clinches it.
Validus, from the Legion of Super-Heroes. A mindless powerhouse, easily controlled by his teammates in the Fatal Five. In the original continuity, he turned to actually be the child of Legion founders Saturn Girl and Lightning Lad (time travel was involved).
DC's Superboy-Prime: An alternate Clark Kent/Kal-El from a world where he was the only superhuman, which was destroyed. After helping to save the universe he spent years in a pocket dimension, (and didn't age or mature past his early teens), which drives him Ax-Crazy. A dose of The Punishment from the Guardians Of Oa gave him the power to traverse dimensions at will and destroy whole planets. To make things worse, he has the power level of the Silver Age Superman (only with a seriously warped morality), almost none of his weaknesses (only red solar energy will keep him in check), and a suit that ensures he is constantly charged with yellow sun energy.
The Flash villain (and later member of the Ineffectual Sympathetic Villains and Terrible Trio Injustice League) Big Sir is extremely large and powerful, but mentally deficient and easily exploited. He was eventually killed by a bio-engineered bomb designed to look like a small child while he was trying to hug it.
Sergeant Crumb, the largest man to serve in the British armed forces, in Adventures in the Rifle Brigade. Possessing strength that is rather unnatural even for a man his size (at one point he punched a man's head clean off his shoulders), and constantly sporting a mindless, toothy smile, he seems incapable of actual speech and only ever says "Ey-oop!" The conclusion reached by his superiors in his official dossier (which mentions several events where he's implied to have killed dozens of people) is: "Mummy, I'm frightened."
Similarly, Corporal Geezer only says "Yer aht of ordah!" and is one of the most prolific murderers in British history, being tried for over 413 murders before evidence was waived when he was assigned to the Rifle Brigade, which desperately needed a maniac like him to tie it together.
Bobby in the opening "Euthanized" story of Hack Slash. A lot of people think Vlad is a rare good example because he talks funny, but he's cleverer than he likes people to think.
Larfleeze fromGreen Lantern has been living alone in a cave for billions of years with everything he's ever wanted being brought to him by his mindless constructs. This has given him the temperament of a spoiled three year old.
And, as seen ins his Christmas Special, he believes in Santa Claus.
The Question villain Baby Gun. He looked like an giant toddler and used an air gun at close range to kill people.
To be clear, he's huge and pretty fat, and probably in his mid-thirties.
When Dream kills him causes him to fall into a magical slumber, he kindly lets him go having a dream that all the (dead) children come back and forgive him, and don't laugh at "the funny big giant," and they all play together forever and ever.
Gideon Gordon Graves, the Big Bad of the Scott Pilgrim series, a Type C with some Type B qualities thrown in there just for fun. He's a wealthy and successful entertainment mogul, and the epitome of a Villain with Good Publicity. However, he seems to have the emotional intelligence of a seven year-old—he's petty, vindictive, possessive, can't handle rejection, and just wants people to adore him, even if he has to make them adore him against their will.
Dirty Ron from the Warren Ellis series "Two Step". Just a simple, giant lad that likes to shag stuff - till it goes boom. He prefers cars to people, but when he wears his VR rig, everyone look to him like a purdy, purdy minicooper.
In the Pony POV Series, the Dark World version of Fluttercruel more than qualifies as a Type E. Despite being over a thousand years old by this point, she's still mentally a foal who, as Rarity puts it, no one ever explained the difference between a hug and a handgun to — she's a sociopath who gets her thrills torturing and killing things, and throws tantrums when Discord won't let her. This is the result as being raised by Discord, which resulted in her belief that she was showing love to her father by torturing ponies and that she was showing her mother love by torturing her.And this is all before she goes off the deep end.
Female version in Hivefled's Condesce, who along with her partner the Grand Highblood has murdered two and a half thousand teenagers for kicks and horrifically tortured her own son while cooing and cuddling him like he's a puppy.
Film - Animated
Scar from The Lion King. Best exemplified when he says "I'm king, I can do whatever I want!"
Kadaj and his group from Final Fantasy VII: Advent Children, a group of superpowered teens created from Sephiroth's refusing-to-be-dead essence. Kadaj, a mix of B and C, can go from vicious and sadistic to heartbreakingly childlike and back again in the span of around fifteen minutes. His older 'brother' Loz also qualifies as type A, being less psychotic, but more childlike. Probably Yazoo as well, as type C. He doesn't get much screentime, but just watch him laughing in childish excitement in the extended version as he steers his motorcycle off an exploding bridge to attack an airborne helicopter.
Syndrome in The Incredibles balances a genius-level talent for inventing technology with an incredible childish personality; he's immature, excitable, petulant, irresponsible, prone to mood swings, obsessed with gadgets and 'toys', and spiteful. His entire motivation also stems from an admittedly wounding and hurtful but still relatively minor slight he suffered when he was a child, which he refuses to move on from.
Prince John from Robin Hood. A petulant, temperamental, selfish, impulsive crybaby who sucks his thumb and cries for his mommy. The real Prince John (later King John) is often depicted this way in other works, but whether he truly was is impossible to say.
Gaston's role in Beauty and the Beast pretty much consists of him throwing a very violent temper tantrum when he doesn't get what he wants.
Michael Myers is actually an aversion. In the original Halloween (1978) he just kills his sister without any real reason. Dr. Loomis describes him as being "pure evil". It wasn't until the remake that he became this. This was a major criticism since it took away from the looming mystique of the original character.
Loki in Dogma. Since Angels apparently don't have a conscience and he used to be the Angel of Death, before resigning when he got pissed, there may be a reason to this.
Norman Bates from 'Psycho has a gangly childishness, due to his mother's isolating and dominating him. It becomes more obvious when Lila Crane snoops through the Bates home and comes across Norman's room.
The movie Mad Max: Beyond Thunderdome, has the title character facing off against "Blaster" in the eponymous Thunderdome. ("Blaster" is the masked, hulking, none-too-bright bodyguard of Master, one of Bartertown's leaders.) Max outthinks Blaster, knocks off his mask, and is all set to kill him when he discovers that Blaster has Down Syndrome and is essentially a child in a giant's body. Max relents, but the people who hired him to kill Blaster aren't feeling quite so charitable...
It's almost obligatory to depict The Joker this way, but the 1989 film takes it a step further by showing him as the apparently sane (but still very, very evil) Jack Napier prior to his transformation. In between the vicious murders he committed as Napier and then continues to commit as the clown he becomes, the Joker "punches out" two television sets with a gag boxing glove, blows into a birthday-party noisemaker (possibly the film's single funniest scene), obsessively cuts up photographs to make collages of them, hosts a parade with giant cartoon-character balloons, makes funny sound effects with his mouth, and sends the woman he's stalking a note written in crayon.
In Batman Returns, the Penguin spends a good deal of screentime wearing only a onesie-like garment stained with his own spittle and slobber. Furthermore, he rides around in a giant toy rubber-duck vehicle and amuses himself with an umbrella (among his collection of genuinely deadly ones) hung with little plastic animals reminiscent of a mobile found in a baby's crib. ("Shit! Picked the cute one!") Actually, the Penguin is more of a Type C - a quite sane and intelligent (though, again, extremely evil) man who simply has not been able to grow up because of his Daddy Issues.
While vandalizing - and ultimately blowing up - a department store owned by the man who attempted to murder her, Catwoman takes some time out from her mischief to girlishly "skip rope" with her trademark bullwhip.
Near the climax of Batman Forever, the Riddler and Two-Face play a game of Battleship that uses real torpedoes - and the Batboat (piloted by Robin) is their target.
The DVD commentary for Thir13en Ghosts provides backstory for the Black Zodiac. This trope is represented by The Dire Mother and The Great Child, the Mother being a little person in a travelling circus and the Child being the result of rape by the circus' Tall Man. He was extremely spoiled by his mother and appeared as a fat, hulking brute of a man wearing diapers and a bib and carrying the axe with which he had killed his mother's murderers.
They're not stupid. They're infants. (Beat) Okay, they're stupid infants.
The Merrye siblings in Spider Baby or, the Maddest Story Ever Told, who have a condition that causes them to revert intellectually until they have childlike minds in full-grown bodies. This enables them to do things like kill deliverymen as part of their games, and demonstrates how excellent it is that humans can be taught morality before they're big enough to do real damage.
Repo! The Genetic Opera's Luigi Largo is a rather brutal murderer, and most of the time seems like a functional adult, but a stern look from his father or a sharp word from Mag can turn him into a contrite toddler. He also throws temper tantrums that would be hilarious if he didn't have a knife in his hand while he had them. At the end of the film, after Rotti's death, he breaks down sobbing in the middle of menacing a crowd of people.
Zigesfeld in If Looks Could Kill displays multiple signs of mental retardation, including a childlike dependence on the film's female villain. When she strokes his mechanical hand in one scene to calm him down, he grins like a little boy.
The towering 'trolley boy' Michael "Lurch" Armstrong in Hot Fuzz. According to Danny, he's a product of incest and has the mind of a child. When the members of the NWA are booked at the end of the movie, he's bawling like an infant
The 1963 film Cleopatraportrayed Octavian (the future Augustus Caesar) as one of these. The historical community was Not Amused.
Don't!, one of the joke movie trailers in Grindhouse, Nick Frost has a cameo as a cannibalistic man-baby locked in the basement of the house. Part of the central joke of the trailer is that everything happens too quickly to get a sense of what kind of horror movie it is, so it's hard to say much more about his character.
Stuntman Mike in Death Proof, one of the actual films featured in Grindhouse. He puts on a suave act, but at his core he's a vindictive juvenile who gets off on doing cruel things to people. His demeanor in the last act, when he comes across some women who fight back, is that of a kid whose prank has backfired on him.
Olaf in The Sinful Dwarf is a particularly frightening and extreme example. He plays around with eerie wind-up toys and uses them to lure girls in to be used as sex slaves. Just watching Olaf can be nauseating.
The eponymous character of The Mask. By the Doctor's analysis, the mask actually makes to surface all the "inner child" from that person, so it fits for all characters ever wearing it.
In Suicide Kings, one of the No Name Given kidnappers holds a gun to his partner's head, cocks the hammer, and begins to pull the trigger...because his partner changed the channel while he was watching a cartoon and wouldn't change it back. After he leaves, the partner checks the cylinder of his gun and finds that it was fully loaded.
Near the end of The Last King of Scotland Nicholas is captured by Idi Amin's men trying to flee the country, tortured and confronted by the dictator, leading to this little exchange:
Idi Amin: I am the father of this nation, Nicholas. And you have most... grossly... offended your father.
Nicholas: (battered and bloody) You are a child. That's what makes you so fucking scary.
The Ghost of Christmas Present from Scrooged is a female example.
Suzanne Stone of To Die For is an evil woman who seduces a (very dim) teenager to get him to kill her husband, and her intellect level is just barely above his, or above a child.
Shinzon of Remus from Star Trek: Nemesis. He initially justifies his actions by a desire to free his people, and then by a desire to unify Romulus and Remus, and then by a desire to remove the threat posed by the Federation...but by the end of the movie, it becomes pretty clear that all that he really cares about is proving his superiority to his "father" Captain Picard.
The various Harry Potter film adaptations portrayal of Bellatrix Lestrange depicts her as having shades of this. For one thing, shortly after murdering Sirius Black, as well as her re-encounter with Harry at the burrow, she taunts Harry about her direct involvement in Sirius Black's death by singing "I killed Sirius Black!" repeatedly in a similar manner to a playground taunt by preschoolers.
In A Fairly Odd Movie: Grow Up, Timmy Turner!, the Big Bad, Hugh J. Magnate, ultimately turns out to be one once he gains access to Cosmo, Wanda, and Poof's magic. This is foreshadowed by the fact his evil lair is designed more like a playland. He says that this came from the fact his father never let him have a real childhood.
Baby Firefly from the Houseof 1000 Corpses films. She cuts the heads off of dolls and nails them to the wall, has a childish high pitched voice and giggle, and recited the Rabbit Hutch rhyme while murdering a woman that she put in a rabbit suit.
William "Wild Bill" Wharton, from The Green Mile, displays shades of type C of this trope, at least in the film. Despite being on death row, his antics seem more childish and goofy than anything else, sometimes being played for laughs, until it's revealed he raped and murdered two little girls while working as a farmhand, a crime for which John Coffey takes the blame.
Coffey himself is viewed this way in-universe, at least by the attorney who prosecuted him. When the main character stops by the attorney's house to protest Coffey's innocence, the attorney tells him about a dog he once owned who would bite people and then act sorry afterward, implying that John Coffey is much the same way.
Butterfinger, the Dumb Muscle of the group of rogue CIA agents in Hudson Hawk. At one point, when the other agents are complaining about how long Hawk is taking with his Love Interest, Butterfinger asks, "You want me to rape 'em?" There's a long, uncomfortable silence, and then one of the other agents hands Butterfinger a book to distract him. It's Dr. Seuss's Green Eggs and Ham, which Butterfinger seems to struggle with.
Agent Lynch from The A-Team acts like a 16-year-old with daddy's credit card and car keys. He leers at his assistant, constantly brags about how much cooler his job is than his opposite number's, and displays childlike glee at all the cool toys he gets and stuff he gets to do.
The movie Game Over has one, in the form of a supercomputer named Drexel, which threatens to destroy the world unless someone plays video games with it. To add to the effect, Drexel is voiced by a child actor.
Pee-wee Herman edges close to this trope in some parts of Pee-wee's Big Adventure, especially when he is shown becoming increasingly obsessed over the theft of his bicycle.
The backwoods rapists in Deliverance might qualify as an example of Type E. They're so deformed due to inbreeding that it's easy to imagine they're mentally retarded as well, and don't understand that rape is wrong or cruel. After one of them forces one of the campers to strip down to his underpants (or "pannies", as the hick creepily refers to them) and then mounts the victim, he pretends he's riding on the back of a pig, playing rather than committing a horrible crime. This would lend an Alternate Character Interpretation to the hicks when they turn even more violent after the campers kill the rapist in self-defense: in their simple minds, they're acting out of righteous anger (or perhaps even self-defense themselves) that these city-slickers would murder one of their own for no reason when they were just trying to have some fun.
Amon Goeth in Schindler's List. He has tantrums like a child, does things on a whim, and likes to break his toys. Unfortunately, in this case, his toys are human beings being starved and worked to death, who he kills on the merest whim (e.g., he wants to kill someone). Accent on the "merest" part.
Goeth's Mistress: "Amon, you're such a damn fucking child!"
Johnny Truelove of Alpha Dog is an impulsive, shortsighted, criminally dumb wannabe gangster trying to project a "tough guy" image. He kidnaps Zach on a whim, threatens people wherever he goes, and doesn't realize how many witnesses he creates because of his own poor planning. He doesn't even keep tabs on the murder he orders while going out with his girlfriend and having fun, and rejects the option his father offers to release Zach and spend minimal jail time even though he has no other plan himself. He remains elusive for so long only because of blind luck.
Gary from The Gamers films is not a villain, but he falls into this territory during his Sanity Slippage at GenCon in Hands of Fate. Most geeks can sympathize with the pain of becoming emotionally invested in something Too Good to Last. But is repeatedly physically assaulting the costumed mascot of the series that you blame for your favorite show's cancellation really the behavior of a sane adult? (It's also worth noting that Ninja Dragon Riders, the late, lamented series in question, appears to have been intended for the Shōnen demographic. So for additional Psychopathic Manchild points, Gary's being driven to violence by his emotional overinvestment in a program intended for twelve year olds.)
Silva from Skyfall has an almost gleeful childlike attitude when it comes to what he does. But it's best exemplified at the end when he realizes M is slowly bleeding to death, he devolves into a whimpering, scared little boy and proceeds to lovingly embrace her while begging her forgiveness.
In X2: X-Men United, thanks to the brain surgery, Jason Stryker's both very easily manipulated and childishly devoted to his abusive father - to the point that when Magneto catches up with him, all he needs to do in order to change Jason's mind is have Mystique transform into Stryker and give him a new set of orders. For good measure, within his illusions, he usually depicts himself as a child.
In one of the creepiest moments in the entire Agatha Christie canon, when the murderer in "Three Blind Mice" finally reveals him/herself to his/her intended last victim, his/her voice suddenly devolves to that of a child.
"I said that I'd kill you all when I grew up and I meant it! I've thought of it ever since! I'm grown up now; grownups can do what they like!"
From the other extreme of the spectrum, the same book features Banjo, an even more child-like thug, who is clearly mentally handicapped, and comes across as much more innocent. And he and Teatime are friends. Or at least, he does what Teatime tells him to while Teatime treats him with dismissive contempt.
Another Pratchett example: First Mate Cox in Nation is at one point given a description suggesting this, when his gleeful expression at shooting down a parrot was compared to a little boy proud of wetting himself. On the other hand, at no other point is he shown as anything but fully, rationally aware of what he is.
"First Mate Cox had a choice, every day, and had chosen to be First Mate Cox."
JJ, the protagonist's vile alter-ego, will gleefully commit murder, vandalism, assault, and any number of crimes for his own childish amusement. However, if anyone responds violently or threateningly, he'll react by bursting into tears and running off.
The Howlers, an ancient race of genocidal warriors in Animorphs. Jake was essentially expecting them to have the mind of a super-predator, but upon morphing into one, he discovers to his shock that they are actually possessed of a childlike simplicity and engage in genocide because they think that it's just a fun game. Eventually, the Animorphs were able to exploit this by revealing to the howlers that their victims are more than just mindless toys which exist for their amusement, thus "ruining" them.
The Somnambulist by Johnathan Barnes features a pair of these, called The Prefects.
The (presumed) Big Bad of The Meq is the Fleur-Du-Mal, who, like the rest of the eponymous race of immortals, is Really 700 Years Old, but he's also a Psycho for Hire with a bone to pick with the rest of his race. He likes to cut throats, kidnap little girls and turn them into prostitutes, dabble in the occult, manipulate normal people, or Giza as they're called, with his appearance as a twelve-year-old boy, and sadistically torment his own kind. Yeah, he's a Jerk Ass.
Soon, Ray's sister, Zuriaa was dangerously unstable and became Fleur-de-mal's twin. What a plot twist.
In the Redwall book Martin The Warrior, the heroes come across a tribe of Chaotic Neutral wild squirrels who live for pleasure and think it would be a really fun game to chase said heroes up a cliff and throw them off! They do end up working for the good guys later on, as they're convinced this would be an even better game. Also, the horribly spoilt Prince Bladd (though his age is unclear, so he may in fact be fairly young). He likes playink mitt fire.
In Tad Williams' Otherland, the Other is the quasi-sentient operating system of the eponymous network. One of its many bizarre attributes is that, despite being at least twenty years old, it seems to have the personality of an autistic child, and at several points in its "development", the Grail Brotherhood attempted to have it communicate with real children, in order to allow it to develop the capability to interact with people. The Driving Question of why an apparently home-grown AI behaves this way is only resolved when it's realized that the Other is not actually an AI; it's a real human child, stolen at birth and implanted as the "brain" of the network.
Lysa Arryn throws tantrums like a spoiled child when things don't go her way and ignores her responsibilities as Lady of the Eyrie in hopes that they would go away. And when her new husband Littlefinger forcefully kisses her niece Sansa, she tried to murder the latter because she believed they tried to steal what belongs to her.
Cersei Lannister covers her inner woman-child with a huge layer of The Vamp (and all the Manipulative Bitchiness that requires) with aspects of Mama Bear in adulthood. But, her primary motivation for much of what she does is what it's basically been since she was very young... a massive tantrum that she can't get the cool toys like the boys do (or, more specifically, like Jaime does). And, Daddy won't look at me like he does him! (So, I'll be better than Daddy!) It's not very pleasant when it combines with a streak viscous enough to advocate torture, murder and, occasionally, outright acting like her brother's (and cousin's) Lady Macbeth when she isn't being her children's My Beloved Smother, so any sympathy you might have for her points about the inherant unfairness in the Stay in the Kitchen attitude of most of Westeros gallops out the window thanks to her general toxicity.
Ramsay Bolton is still the little boy who pulls the wings off flies, roasts living grasshoppers, drowns kittens and beats nerds for lunch money whenever he feels like it inside. Just all grown up enough to add raping and flaying people to the list of things he enjoys doing.
First is Jeff. He acts incredibly childish and has exaggerated opinion of himself. He throws a fit whenever he doesn't get his way and is generally an all-around douchebag.
Second is Gansetseng. She's actually over three hundred years old, but she was turned when she was just twelve and hasn't physically aged since, and has barely aged emotionally thanks to her "father" (actually her some odd great-grandfather) treating her like a child for all her life.
According to The Disaster Artist, Tommy Wiseau is pretty much this as he acts very childish throughout the book, even when he's trying to manipulate someone.
John Dies at the End has an interesting example in that the Psychopathic Manchild is Korrok, a gigantic amorphous Eldritch Abomination with the mental maturity of a 13 year-old who just discovered his first batch of cuss words. People under his control tend to do things like blurt out offensive comments and do strange and depraved acts like stripping naked in the middle of the street and packing snow onto their crotch or pissing on the hood of the protagonist's car, and his idea of tormenting the protagonist is to turn on his car radio and replace all the song lyrics with racist diatribes. When Dave and John finally meet him, Dave notices that his voice sounds like a toddler's.
Lennie in Of Mice and Men could be considered this, aside from the fact that he is not psychopathic. Unless you count the fact that he outright murdered Curley's wife because she was screaming. And she was only screaming because he was hurting her, and wouldn't let go of her.
Live Action TV
Todd from Breaking Bad turns out to be a rather understated case of this trope. He appears to be at least in his mid to late 20s but acts a lot more like an awkward 14 year old. Most of the time he tries to be polite and considerate to other people but it often seems like an imitation rather than anything real. He also ends up carrying out the most shocking atrocities in the series: Casually shooting a child, torturing Jesse to learn what he told the DEA and to cook meth for him, murdering Andrea to keep Jesse cooking for them, and intimidating Skyler by threatening to kill her infant Holly.Murder seem to mean nothing to him whatsoever.
Battlestar Galactica: John Cavil is eventually revealed as an angsty teen stuck in an old man's body with a load of Mommy Issues to boot since said old man's body was based on his "mother" Ellen Tigh's father (it's probably a good thing she didn't know that when he forced her to have sex with him). He also killed his brother(s) Daniel out of jealousy.
Blackadder II gives this treatment to Queen Elizabeth I, of all people.
Al Capone in Boardwalk Empire shoots Jimmy Darmody's pillow while he was sleeping as a joke. He also gives his boss Johnny Torrio an exploding joke cigarette in the middle of a meeting. Johnny is not amused.
Chang on Community enjoys wielding the power of being a teacher a little too much, and is shown to be very immature playing mind games with his classes.
Many of the serial killers in Criminal Minds are emotionally stunted, but special mention goes to the killer in the two part "To Hell ... And Back", an emotionally and mentally retarded middle-aged man whose quadriplegic brother directed to pick up transients and use them in the smarter brothers' experiments.
Joe, the mentally retarded Monster Clown from "Damaged". Despite being in at least his thirties, he's extremely childlike, when he's finally caught he weeps like a child and screams for his daddy. But don't feel too sorry for him he stalked a little girl through a carnival, then broke into her home and murdered her parents with an axe. For twenty years he was That One Case to Rossi.
There is also Cy in "Proof", who, despite being born with brain damage, is unsympathetic. The reason for this is that, unlike the examples above, there is no indication that Cy's mental handicap is the cause of his behaviour; for all his childishness, he is not incapable of knowing right from wrong, and says that he learned when he was a child that kicking his dog was fun, and he kills for the same reason. He also has the same misogyny as many other killers, takes trophies of his victims, and plans to avenge perceived wrongs by making his brother watch the tape of Cy mutilating his daughter, and by the end of the episode it's clear that, even without his handicap, he would still be a Serial Killer (and a particularly sadistic one at that, he rapes and takes away his victims' senses with sulphuric acid to kill them).
The most recent one, a guy who transformed his victims into actual People Puppets, at least has the excuse that a serious brain injury caused his personality to revert back to his childhood when his puppeteer father was murdered by a robber; he was young enough that he thought the puppets were real and didn't understand why they didn't help when they were hanging right behind the robber.
The title character in the Doctor Who story "The Celestial Toymaker". Lose his games and you become one of his toys. Win and he destroys the world. By the way, he cheats a lot.
The Master (Simm edition) in Doctor Who giggles, makes faces, takes a childlike pleasure in the Teletubbies, and dances around the room to pop music while taking over the world and ordering the annihilation of millions of people. His Toclafane ( humans from the far future) are floating balls that are childlike, and kill "because it's fun".
The Gods of Ragnarok in The Greatest Show in the Galaxy are extremely powerful beings who have been completely consumed by the desire to be entertained 24/7 (or whatever Segonax's day is). One of them even manifests as a child.
Melody Pond. She gets better.
Dollhouse has Terry Karens, a wealthy serial killer who loved to "play house" by paralyzing and posing his victims like dolls.
Topher in the first season probably qualifies. (He starts to develop a bit of a conscience later in the second season.)
Fringe's Walter Bishop is a seemingly harmless Mad Scientist and pretty likeable, until you remember he experimented on children in order to communicate with other dimensions, has created horrible monsters and oodles of other universe smashing stuff.
Sylar himself is a Type C. He's shown to be extremely powerful and ruthless, but also indulges in childish behavior to deeply freak people out. He's also shown to treat abilities like a toy collection, even explicitly calling Maya a shiny new toy to play with.
Jackman's Hyde persona from Jekyll is repeatedly stated to be a child who just happens to have the intelligence and drives of a full grown man.
Kamen Rider OOO has three of these. Kazari, a childish Chess Master, Gamel, whose a little lacking on the "psychopathic" part but still a destructive and childish kaijin, and Lost Ankh, Ankh's body that obtained sentience and has the mind of a child, but is none the less evil and destructive.
Law & Order: SVU gets one in its tenth season with CSU Tech Dale Stuckey; in the season finale, Stuckey kills several innocent people to try and frame a psychotic man who'd killed before, kills his CSU boss before he can tell the police he was the actual killer, and starts assaulting Stabler with the intent to kill him before Benson makes the save.
One flasher-turned-child rapist is a severely stunted man who knew he had a problem as a teen but his dad used it (and his cameras) after having his son watch him with prostitutes, than watching his son with prostitutes wasn't enough to get him off. Olivia feels very, very sorry for him.
Cyril O'Reilly from Oz, an Irish gangster who became retarded after a blow to the head. He also has the bad luck of having a Manipulative Bastard brother whose orders land him in jail. Though he's normally quite good natured, he becomes one of the more feared inmates as a very strong man who's easy to set off.
Gem and Gemma from Power Rangers RPM are a rare heroic example. They're intellectually geniuses, but in everything except physics and technology, they're about five.
They are also really fond of violence in general, and explosives in particular.
Joey Heric of The Practice was sociopathic, calculating and exhibited a very childish attitude such as announcing "I need to pee" to stop a trial session to get his way out of his own murder trials.
"Charlie X," full-stop. A human child raised by omnipotent aliens and given the ability to warp reality. Though 18 years old, he has the social skills of a spoiled five year old. Having committed mass murder before being picked up by the Enterprise, he causes so much carnage upon the crew of the enterprise (which the aliens ultimately undo) that he is handed back to the aliens at the end of the episode.
"Whom Gods Destroy" involves one of Kirk's heroes gone insane from a head injury during a starship crash. Imprisoned in an institution for the criminally insane, he starts screaming at the top of his lungs and banging his fist on the floor when he can't impersonate Captain Kirk well enough to be allowed onto the Enterprise. Most other patients exhibit this trope. They exhibit "entertainment" to Kirk in the form of wheelbarrow racing in a circle. One patient defends accusations she plagiarized a poem from A.E. Houseman by saying she "wrote it again this morning" and craves attention from all the other inmates. The hero in question was played byWilliam Shatner.
But only when the once-hero-gone-insane is impersonating Kirk, yes? If not, then someone's incredible make-up skills should also have been put to use in "Arena" (for starters).
Trelane of The Squire of Gothos starts out merely childish, becomes villainous (but still childish) when crossed... and ultimately turns out tobe a child. Not a human child (his species is apparently far beyond humanity), and he appears as an adult human, but still a child whose parents come to pick him up, apologize for his misdeeds and punish him when he's been naughty.
Another Star Trek example, this time from Star Trek: The Next Generation: The entire Q race at times comes across as this. Omnipotent and godlike in power, while gleefully using their power to manipulate, bully and otherwise annoy "less evolved" species, while reacting with indignation when these species actually call them out on their behavior. The Q played by John DeLancie, with whom the crew most-frequently interacts, has a particular reputation for this sort of behavior even among his own people and is very much The Trickster. Except when he runs into Ben Sisko, who unlike Picard is not about to put up with his crap and outright decks him when pushed too far. His son takes it Up to Eleven.
Lucas Taylor in Terra Novaseeks to destroy Terra Nova and the entire world in which it is located killing over a thousand innocent people, all because he wants to get back at his father for not saving his mother when he was a teenager and generally not giving him enough attention growing up proving that being a genius scientist is no bar to living up to this trope.
Klaus and Damon on The Vampire Diaries. Both are reckless, ruthless, sociopathic yet somewhat immature at the same time.
Franklin from True Blood plays this trope straight off into the distance.
Emperor Cartagia from Babylon 5 is thouroughly insane and monstrous, but his cruel antics have a distinctively petty and childish taste. He's like a dim-witted bully tormenting a cat. He would dance a merry dance with the court jester and then have him executed for mocking him, goes all sulky when despite all his efforts, he cannot get a scream out of his victim, and acts annoyed that he has to make all the decisions, when asked which of the victim's eyes he would like to be put out. Hell, he sentences his entire planet to destruction, because he was promised to be made a god if he does.
Paulie Walnuts from The Sopranos is the perfect(ly nightmarish) combination of the petty self-centeredness of a spoiled child with the total disregard for human life of a stone-cold murderer.
Marlowe Viccellio from Psych. Apparently a normal woman when we first meet her, she is arrested for stealing blood (it was to save her brother's life) and sent to a California women's prison, where she quite abruptly turned into this. Given the nature of the show, this is Played for Laughs, with a scene of Marlowe acting cute and flirty with her boyfriend (ironically, a police detective) when he comes to visit her and then, seconds later, joining the rest of the inmates in a violent attack on the guards when they start a riot during a prison variety show. Later, when she is released from prison, Marlowe proves to be perfectly sane; her "crazy" shtick had been an act to endear herself to the other inmates - which is more heroic than it sounds, because the detectives needed her to cozy up to Santa Barbara's most notorious female gangster in order to uncover some clues toward solving a gang shooting.
Marlowe:(sweetly to Carlton Lassiter as the riot begins) Duty calls. (viciously, into the crowd) I will cut you, Debbie!
Helena from Orphan Black is an especially creepy version of this. She has some mannerisms of a child (curiousity, Big Eater tendencies, somewhat childish way of talking) and is just all-around weird. Unlike most examples though, she knows just how dangerous she is. She's just that screwed up. She leaves clues that lead the police profiler to conclude that she had a bad childhood: mutilated dolls, bloodied paper fortune-tellers, stick figure sketches. She also plays on the bed when she breaks in Beth and Paul's apartment, eats jello with extra sugar, and wants to see Olivier's tail. None of this diminishes how threatening she is and how far she's willing to go "cleanse" the other clones.
Justified: Coover Bennett is the classic "Dumb Muscle bruiser" type. Very dim, and possessing the emotional range of an eight year old, Coover's entire life is built around pleasing his mother and brothers, and he throws violent tempertantrums when he can't get his way. His older brother Dickie is a slightly more mature example, who is psychologically trapped at the moment in high school when protagonist Raylan Givens broke his knee, leaving him with his trademark limp.
Lucifer from Supernatural for all his power, wisdom and affable evilness, is revealed to be nothing more than an "bratty child throwing a temper tantrum". His destruction of the human race is due to him being jealous that God favored humans more than him, essentially making the Apocalypse one big family argument.
Lilith, who possesses young girls and torments/slowly murders their family for fun.
The Walker, Texas Ranger episode "Deadly Vision" involved a man who abducts children to play with him, he would claim them as his own and kill anyone who tried to take them from him, and if the children angered him enough he would murder them.
The main character of the Thomas Fersen song and music video "Hyacinth".
George Steele, during his heel run. He then became a sympathetic baby face, all without really changing his in-ring style.
The gimmick of Abyss in TNA is this trope. When he's a face, the sympathy is milked for all it's worth.
The Great Khali is this by default (Type A) during his heel runs. In-universe, he's a gigantic, physically and mentally stunted Indian immigrant who usually just wants to kiss girls and dance to Bollywood musical scores, but unfortunately is just sostupid that it's relatively easy for his much more evil "friends" to warp his mind and turn his phenomenal physical strength toward malevolent purposes. The last of these slavemasters was Jinder Mahal, who not only mentally manipulated Khali but idiotically tried to physically bully him as well, leading to the Crowning Moment of Awesome of Khali finally getting thoroughly sick of Mahal's bossiness and brain-chopping him into submission.
In Mel Brooks' Young Frankenstein, on the other hand, he's a standard-issue Manchild (at least until the end, where he... ah... stops being anything of the sort). On the other hand, he does come across as being smarter than some of the other characters....
Of all the violent raving madmen in this universe, fandom chose to make Ax-CrazyBlood KnightKharn the Betrayer this of all people. Read this collection to see the Champion of Khorne (what a fun guy) engage in activities like finger painting with blood, arranging bodies into amusing messages, and jumping into combat from high orbit (the narrator ended up surfing a Khornate Space Marine).
One of the Iron Warriors short stories has the Slaughterman, who is described specifically as having a child's unthinking cruelty. He doesn't come to a good end.
Goblins in the Pathfinder setting have this kind of persona. They're such immature, comically inept little guys that they'd count as Ineffectual Sympathetic Villains if not for their rare moments of competence at murdering innocent noncombatants. In fact, each of the goblinoid races in Pathfinder (goblins, hobgoblins and bugbears) are meant to represent a different kind of evil and the little buggers represent childish random malice incarnate.
One of the most frightening and powerful incarnations of this trope is seen in the Dungeons & Dragons Demon Lord Kostchtchie, who rules a whole layer of the abyss based soley on sheer power and child like rage. It helps that he's secretly a pawn to Iggwilv, but still, most Demon Lords can't rise to the position, let alone hold onto it, without having shades of the Magnificent Bastard.
The Fair Folk of Exalted are mostly this. They don't mean to be horrible, horrible monsters, but they don't understand how reality works. They hail from the Wyld, where most any being they encounter is simply a figment of either their imagination or another Fae's, so they have difficulty processing the idea that every individual they meet in Creation is an independent and sentient being. Furthermore, in the Wyld, Death Is Cheap. A Fae killed by another Fae can just shape himself back into existence with a thought, so they have trouble understanding why the Creation-born are so uptight about the stabbing.
Poison in Dracula: A Love Stronger Than Death is a female example, a fully-grown vampire woman who affects an infantile attitude and carries around an identically-dressed doll while wearing babydoll dresses herself, and takes childish delight in the evil that comes with being a vampire.
Lance Vance in Grand Theft Auto: Vice City Stories. He is an adult and a drug dealer, and is probably the only character in the entire series, at least in this sequel, acting childish, but nevertheless, is a sadistic murderer.
The Boomers in Gears of War and other Locusts of his size. The other locusts use cover effectively and yell orders to each other. The Boomer stands out in the open, points his gun in the general direction of the enemy, and dutifully says "Boom" before firing. That's all he ever says.
The oh-so-bland "SKY FIRE" when you fire a mortar.
The heroes themselves can come off as the "perpetual teenager" versions of this at times - especially Cole who (among other things) hijacks a Reaver and names it "Horsey".
Ramon Salazar of Resident Evil 4 has the build and proportions of a nine-year old, the skin of a sixty-year old, and claims to be twenty. He's also fucking nuts and suffers a severe Villainous Breakdown over the course of the game.
A less hilarious, more tragic example would be Lisa Trevor. After decades of Umbrella experiments, she's a powerful, seemingly unkillable monster with the faces of some of her victims sewed together and worn like a mask. Despite all this, her mind is that of a very young child, desperately searching for her mother.
Arguably GLaDOS of Portal. Her demeanour and behaviour certainly brings to mind a surly child, doing mocking impressions of Chell ("That's you! That's how dumb you sound!") and giving childish retorts ("If you love it so much why don't you marry it? Well, I won't let you!).
The turrets and their child-like voices. "Hello, friend. I see you. Are you still there? Good night. Put me down! Malfunction. I don't blame you..."
"No hard feelings..."
GLaDOS also smacks of a naggy mother taken to the logical extreme, neatly encapsulating both extremes in one package.
And GLaDOS' creepy red core. Her yellow is curious ("Do you smell something burning?") her blue rattles off cake mix...plus other things ("Don't forget food garnishes such as: [...] fish-shaped dirt.") and the red is...er...well, it doesn't speak—instead it snarls and shrieks at you.
Wheatley, by the end.
From Mother 3, Porky Minch, the Pig King. Justified in that he extensively travelled through time after the end of EarthBound and only aged outwardly - he even describes himself as possibly being 10,000 years old or even older, yet still being the same kid inside, though he said it with the implication that that's somehow a good thing.
Debilitas, the hulking gardener from Haunting Ground, is the only one of the stalkers pursuing Fiona who doesn't have overtly sinister motives - he mistakes her for a 'big doll' and just wants to play. Unfortunately, his idea of playing is a little too rough for poor Fiona...
Achenar, from the game Myst, has a childish way of relating horrific thoughts and events to the player, even speaking in a mocking, higher-pitched voice and giggling like he's just thought of some ridiculous joke. The effect is unnerving, to say the least.
The Igniter bloodline from Bloodline Champions has animations that give one this feeling about them: their running animations looks like skipping, their standing animation is them strangely tilting their head to the left with their right palm up, and their idle animation is hopping up and down left and right on the spot.
Walter Sullivan from Silent Hill 4. He kills people because he believes that he can resurrect his "mom" that way. Note that said "mom" is in fact a room in an apartment complex - his birth mother abandoned him there when he was a baby.
And, while more tragic than psychotic, Angela Orosco. She routinely flips between being a normal woman, a suicidally depressed woman, a psychotic and hateful woman, an innocent child and a psychotic and terrified child. Sometimes in the space of less than a minute. But given what her father did to her it's not that surprising.
Chesty, from a Fable II sidequest, takes the concept of Nightmare Fuel and cranks it Up to Eleven thanks to having this personality...including not seeming to understand that his new "Super Best Friend" really isn't having fun during his Monster rush.
This super best friend had fun. She felt lucky to be able to do it twice thanks to a bug.
This super best friend was particularly happy when the game gave him back his lost youth.
Many if not most of the TF 2 characters have shades of this.
Shadow from the Sonic the Hedgehog series is an adorable little boy. He looks up to his friend Maria, whose terminal illness he was created to cure. They reflect on what life must be like on earth. Even after her death, he shapes his life like a fairy tale, would do anything Maria asked him, and often whines pitifully about who he is and what he's there for. He also thought that the peaceful Maria would want him to avenge her by destroying the planet, is obsessed with his status as the ultimate lifeform, values human life and happiness very little unless he associates it with Maria or himself, and loves guns.
YMMV with Shadow. Still, it's possible; seeing the one person who supported him the most and who he saw as a moral figure murdered in front of his eyes probably disturbed him to the point of becoming this trope.
Eggman's plans evolved over the course of the series from Taking Over The World (and defeating Sonic) to taking over the world (and defeating Sonic) in order to...build a giant amusement park?
Ellis is just WAAAAAAAY too happy during the zombie apocalypse. It's almost as if he views it as a big game Unless someone dies
"Ho-lee-SHIT guys! It's KIDDIE LAND!!!"
According to Nick, "He's like a five year old. With guns. And a comprehensive grasp of every swear word in the English language."
The XT-002 Deconstructor fight in World of Warcraft is a robot version of this. When you aggro it, it says "New toys? For me? Oh, I promise I won't break them this time!"; when a player is killed during the fight, "I guess it doesn't bend that way!" and "I think I broke it!" and one of its attacks is it pounding on the floor shouting "No, NO, NO, NO, NO, NO, NO, NO!", all in the voice of a small child.
Background material indicates that Mimiron (his also-robotic maker) considers XT his son and, as such, built him to have a childlike character. It kinda justifies XT's childishness but not his Axe Crazy.
Mimiron himself mildly shows tendencies of being one. Not as a whole but some of his comments ("MEDIIIIC!") give a good idea about why XT was built the way he is. Unlike the most versions of this trope, however, Mimiron is a borderline genius.
Borderline? He's the god of invention.
Well to be fair at this point he is borderline, as all the bosses in Ulduar are Completly bonkers, thanks to good Old Good old Yoggy, being the Old God of Death and his powers being the power of inducing insanity into living beings.
Many of the undead abominations (giant bloated zombies made from multiple corpses) count as well. Patchwerk is well-known for his creepy childish lines:
Patchwerk: "Patchwerk want to play..."
Jackle from NiGHTS Into Dreams is a literal psychopath whose lair looks like a small child's play room; complete with teddy bears, a merry-go-round, and a guillotine.
Tira from Soul Calibur is more or less Type E. She has such an extreme case of bipolar disorder that it has separated her into two personalities: "Jolly" and "Gloomy". When "Jolly", she talks like a little girl and refers to people as if they are playthings, and gets a thrill from breaking them in the most perverse and sadistic ways, as evidenced by her win quotes. When "Gloomy", she becomes extremely cynical and is willing to harm herself to inflict damage on her opponent.
John DeFoe of the Chzo Mythos is essentially this, seeing as he was raised alone in the basement of DeFoe manor after being disowned by his father, whom he considers an abomination and resposible for his wife's death. Being posessed by the Tall Man after he was beaten about the head and neck with a wooden idol containing his soul certainly didn't help.
In Tales of the Abyss, despite being at least 16 Arietta acts like a small child and apparently cannot handle the news of her beloved Ion death so they lied to her and said that the clone was him. She is also one of the fiercest fighters and one of The Woobie (but they are pretty common in this game)
We have The Beloved in Bayonetta. Big and stupid with cherubic masks on their hideous heads. There are no pretty angels in this game.
Chidori from Persona 3 fits this to some extent. She has a fairly simple vocabulary for the most part, hasn't the faintest idea of how to deal with falling in love, and throws some pretty impressive temper tantrums when deprived of the gun-like Evoker she seems to treat as a comfort object. On the flip side, she works nights enacting revenge for people and has no problem with committing the occasional bit of telepathic breaking and entering.
Matt Helms in No More Heroes 2. He's an undead who in his childhood made a deal with the devil, resulting in him going crazy. And all through his battle he laughs like a little child.
Half the cast of the Touhou says "hi". In particular, Flandre Scarlet, a vampire that looks like a little girl with the explicitly-defined power to destroy anything and a love for games that involve breaking her "toys".
The Demiurge is portrayed this way in Shin Megami Tensei: Strange Journey. He never ceases to scream when addressed, knocks out Metatron, not caring he's got the Pieces of God necessary to restore his mind, and keeps bellowing he wants worship and praise as the Creator.
Grunt from Mass Effect 2 shows shades of this. At one point, he talks about killing the other "weaker" species, all the while pointing out how funny that would be with a child-like glee. He also likes sweets and plays with action figures. However this is justified for two reasons. He is a krogan, and being Ax-CrazyBlood Knights is a major part of the krogan hat. Also, he was grown in a vat and is less than a year old.
Purge from Space Channel 5 Part 2. He likes to play "games". And as heroic characters such as President Peace and later Jaguar are unwillingly forced to take you on, he just laughs and at one point even DANCES happilly as they struggle in pain. He even goes as far as to have a temper tantrum and charges up the Ballistic Groove Gun to destroy everyone, including himself for ruining his plan. The game hints that he doesn't know love somehow, but it still doesn't keep it from being slightly disturbing.
"Time for a game! If you shoot like normal, you'll hit the president!"
Albedo from Xenosaga, especially with his interactions with MOMO and Jr. In the first game, he giggles at the sight of a Kirschwasser he tore apart and demonstrates his ability to regenerate as if he was performing a magic show.
Kefka from Final Fantasy VI was written as one of these in the original, Japanese script. He uses the first person singular verb "bokuchin", which is what little boys use when joking around or trying to act sweet. This idea was left untranslated in the English localisation.
A hint of this snuck its way into Dissidia: Final Fantasy, where he talks about battle as playtime during his fight with Terra, as well as his referring to his opponents as "toys."
As well as in Duodecim, where he remarks that his fight with Vaan was "The most fun [Kefka's] had in minutes." in an over the top, high-pitched, giddy voice.
Caesar in Fallout: New Vegas is Type C. Charismatic, smart, and drunk on the power he coveted since he was a child in the Followers of The Apocalypse. Reading the flavor content in the back of the Prima Collectors Edition Guide reveals that he was petulant and gloryhounding ever since he was a boy. And if you rebuke him during a face-to-face visit, he throws quite a temper tantrum. He's like the Last King of Scotland: He's childlike, that's why he's so scary.
Fallout 3 has Dr. Stanislaus Braun, the overseer of Vault 112/Tranquility Lane; having trapped the Vault residents in a virtual reality simulation, he's spent the last two hundred years using them as playthings for his own twisted amusement, torturing and killing them over and over again in countless gruesome ways. For good measure, in the VR's latest simulation, he's assumed the form of a spiteful little girl named Betty. Lastly, if you succeed in permanently mercy-killing his victims, Braun will throw a temper-tantrum over not having "anyone to play with anymore."
The dumber Super Mutants throughout the series, especially the Capital Wasteland ones.
Mileena has been repurposed as a Type E variant in Mortal Kombat 9. Possessing the mentality of a young girl, she giggles her way through fights and seems to see butchering people as a fun hobby. One of the challenges in the Challenge Tower consists of her trying to force Scorpion to take a teddy bear she made.
In Double Switch, Eddie seems to be this. He seems like a normal Nice Guy who is a genius. Unfortunately, he wants an Egyptian statue so badly that he will hurt or kill to get it. He seems to be bothered by what people say about him at some points. It is also pretty sad to see him reduced to crying "Mom! Mommy!" by the end of the game.
Dr. Angus Bumby from Alice: Madness Returns is a rather subtle version of one whose childish behavior doesn't become clear until well into the story. While, normally, he seems calm and well-educated, as the story unfolds it becomes clear that he's just a possessive child unable to deal with being told no after raping Alice's sister, Elizabeth, seeing her refusals as teasing and then covering it up by burning down their house with them inside. Even the Dollmaker, his Wonderland counterpart uses childish suggestive motions with his hands throughout its boss fight. And, finally, in the end he takes time to gloat at Alice over using his hypnosis therapy to brainwash children into prostitution, that he will get away with it, and continues arguing that he has done nothing wrong.
Ignus from Planescape: Tormentreally likes fire. Including watching fire, setting other things on fire, and being on fire. His mind is also so damaged(being turned into a conduit to the Elemental Plane of Fire will do that to you) that he doesn't seem fully aware that other people don't share his enthusiasm for this.
There's also the Goliaths, slow-witted giants who apparently regard combat as "play time", and the psycho bandits, who ramble all sorts of nonsense (often about their mothers) as they try to kill you.
Mr. Torgue from the DLC pack "Mr. Torgue's Campaign of Carnage" is a likable guy, but he's very loud, loves cookies, is obsessed with explosions and manliness, and writes everything in crayon. He also bonds quickly with explosives-loving Creepy Child Tiny Tina.
The Brutes in Command & Conquer: Red Alert 2: Yuri's Revenge are mutated humans with an Incredible-Hulk like physique, who can kill tanks with their bare hands. They also have the mentality of a five-year old, look on fighting as "playing" and when damaged sob about how they want to go home.
The Grinder Tank introduced in Command & Conquer: Red Alert 3: Uprising is similar: they're basically weaponised steamrollers that can grind anything and anybody that crosses their path into a mangled mess. They go about their work with the intelligence and emotional state of children, giggling about much fun it is to break their "toys".
Who wants to play?
We here to crush!
Go tank! Go tank!
He go bye-bye...
Here I coo-oome!
Make him look funny.
I break all my toys!
Ouch! That hurts!
They're picking on me!
I just wanted to play...
The Boogeyman from Cause of Death. After a burglar (unwittingly) saved him from a lifetime of abuse by killing his parents, he recruited Eli to help in further burglaries. Eli, meanwhile, thought saving him from abuse was the whole point of Jeb killing his parents. So what does he do? He starts killing other abusive parents in turn. And he simply cannot get rid of the trappings of childhood, such as treehouses. He genuinely wants to befriend and play with the children he rescues (and no, those aren't euphemisms), but honestly can't comprehend that he's traumatizing them instead.
The Advance Wars series has Penny from Days of Ruin and Lash from the other games. Penny's mind is so far gone she doesn't even have a grasp of good or evil, and can only be pointed at an enemy army and told "go play". Lash on the other hand definitely acts like one but can also act dead serious at the drop of a hat and is Dangerously Genre Savvy, and neither the player or the characters in the game can decide if it's an act or if she has a Split Personality.
Bobby Barrows, the original Scissorman from the Clock Tower series is a solid type B. He giggles playfully and dances for joy every time he overpowers you with his massive scissors, unless your health is low. Then he just impales you. The second Scissorman (Bobby's brother Dan) is much more of a type C as he's intelligent and capable enough to be a Manipulative Bastard.
Fawful in the Mario & Luigi series. He may be a genius Mad Scientist with world domination ambitions and be one of the villains in two different games, but he's also one of the most crazy, childish and overly unhinged characters in the franchise, with an attitude that can be summed up as this trope meets the Narcissist. He especially like to chortle, laugh or joke about his plans and the presumed imminent demise of his enemies.
Scarlet Briar in the Guild Wars 2 is a type C. She is a genius who is behind many of the major storylines from the Living World's first season, but also treats her crimes as games and her victims as toys to amuse her.
Thog from The Order of the Stick is a half-orc fighter/barbarian with extremely violent tendencies, a sunny disposition, and an Intelligence score that's probably no higher than 5. Thog is probably the only person alive who gets along equally well with Elan and Nale. Elan and Thog bond over the "Manchild" part, and Nale appreciates the "Psychopathic" part. Xykon, the Big Bad, occasionally has some childish tendencies.
Though more intelligent than Thog, Nale himself falls into this trope once he stabs his own brother simply for not wanting to join his group.
Richard from Looking for Group often shows childish tendencies and extremely bratty and whimsical behaviour.
Tim the ogre would be a textbook psychopathic manchild (he refers to Cale'Anon as "Chicken", ex. "Chicken needs squishy?"), but has been described by one of his associates as being taking one too many maces to the head.
Tim is certainly a manchild, but he is really not the violent psychopathic sort.
Reakk: Even though he's a demon who eats people's souls, it's hard not to like the dimwitted little guy.
Oasis, with her underdeveloped personality and sadistic fondness of killing. Bun-bun described her as a "demented toddler", and while she's theoretically opposed to killing innocents, once she eliminates someone from that category, she's willing to do things such as cut their ribs out one at a time out of curiosity while they're still alive.
Kharla'ggen of Drowtales is clearly insane and enjoys turning people into living dolls unable to move, but it's implied she's not actually that bad a person under her insanity. Being under the thumb of a Psycho for Hire who used her as a figurehead leader didn't help her at all.
Fighter is a Type A, who generally enjoys beating the living shit out of people, but is quite friendly and rather... slow.
Ethan from Ctrl+Alt+Del, who is almost completely bereft of maturity and/or responsibility, even from his own actions. He's Family Guys Peter Griffin, except he's a gamer. Yup.
Lawler of White Noise could be considered this. He's a skilled, ruthless, cheerfully sadistic operative who's obviously quite a few bananas short of a bunch. Yet he has a child-like unquestioning devotion to his boss, and spends his spare time having fun by drawing all over his hands. Aww.
Spot of Get Medieval has a childlike enthusiasm for fire and explosions and pure hate for those who try to stop him from making either.
Jared of Jared, despite being very intelligent and a Badass, is childishly selfish and obsessive.
Slick, the devil and God (!) show such tendencies in Sinfest.
Homestuck: Lord English is still the same immature jerk he was when he was young. Explained in-universe as the result of him killing Calliope, his Good Split Personality, before one of them could suppress the other normally for their species. Had he waited, he'd still presumably be just as violent; he just wouldn't be so childish about i.
Quant from Tower of God is a Ranker of the Tower, a position commanding great respect and implying a terrifying amount of power, which he does possess. His greatest weakness is his incredible immaturity, which not only let him self get lead on twice by the examinees he had to train and test, but also caused 197 people to die because he didn't give a shit about concocting a complicated preliminary exam and just settled with a 30 minute death match.
Schlock of Schlock Mercenary manages to combine this with Sergeant Rock to make for one dangerous blob of ambulatory goo. He's childish, violent, loves Stuff Blowing Up, can and will eat anything he can fit in his mouth, (including people) and the idea of having his hand-held rotary cannon effectively turned into a personal artillery field piece rigged to fire grenade rounds gives him a gleeful expression like a kid on Christmas. Oh, and for a brief period he was Dual Wieldingsawed off starship cannons. He's by no means stupid, proving on several occasions to be a cunning tactician and combat leader, but his Blood Knight tendencies and immaturity pretty much guarantees he'll never be promoted above sergeant. And so long as he gets let off his leash to indulge in a bit of ultra-violence he's probably ok with that.
The titular Axe Cop has a sort of meta-justification in that he's actually written by a small child.
Pretty Pink Ponytails from Angel Of Death is a twenty year old woman who has a high pitched voice, wears cloths made for small children (they're cut apart, and have extra fabric added to them.) She skips everywhere and loves to sing nursery rhymes. She also seems to enjoy torturing people and often describes things like death how a little girl would, despite seeming to comprehend these things fully. She also uses brightly colored handguns, and loves explosions.
It should be noted that it's not entirely clear if she really thinks she's a little girl, feels compelled to act like a little girl, or is just taking on the persona of a little girl. If the latter is the case, then she seems to keep up the act 24/7, as she's never been seen out of character, even in private conversations with her brother.
Blaine Eno and Cillian Crowe from Survival of the Fittest are each brutal killers brought onto the island specifically to spice up the competition (it's implied that the terrorists actually broke Cillian out of his asylum to take him to the island), but Blaine is mentally and emotionally seven years old and has no real grip on what he's doing, while Cillian is almost under the control of an imaginary, daemonic, friend named Haddy.
Lately Liam "Brook" Brooks has shown signs of being one of these after having some Sanity Slippage which resulted in Ax-Crazy tendencies.
Freeza comes off as intelligent and cool-headed at first, but when it comes down to it he's really more like a bored rich kid who gets his entertainment from killing innocent people. As he loses more of his cool, his immaturity shows.
The title character of Salad Fingers, though this may be a subversion as he's more True Neutral in the "uncaring, detached, and having no regard for either good or evil" sense.
The Nostalgia Critic is a Type B. Imagine him as a twelve year old boy with no supervision and a gun and you get the idea.
The Nostalgia Chick is a Type D. You get the impression sometimes that she genuinely doesn't know why Nella would be pissed off about cameras placed in her bedroom. And there's no guilt involved either.
Elisa's characters Dr. Tease and The Makeover Fairy both enjoy torturing people through science and makeovers far too much.
Jalix 'Trap-Deezy' has shades of this, often exploding into tirades of excessive alliterative insults at people for even doing the most harmless of apparently "stupid things". Also having a fondness for cute things, littering his videos with inane babble and odd images and making videos where he almost always appears as an intelligent yet morally divorced teenager with world-views beyond his years and an aversion to people, watching his serious videos is just plain awkward.
The Downfallparodies' portrayal of Adolf Hitler is this. To name a couple examples, get his Xbox Live account banned or give him a Wii instead of a PlayStation 3 for Christmas, and he'll rant up a storm.
Peter Griffin from Family Guy is essentially, Archie Bunker with half the IQ points. He is a bumblingAl Bundy type, who more often than not causes most of the conflicts in the show due to his selfishness or idiocy.
Glenn Quagmire, Carter Pewterschmidt and even Cleveland have become psychopathically childish adults in recent seasons.
Toyman of the DCAU, recreated as a childish madman who wears a doll head with a creepy smile.
The comic book sequel of Batman: Mask of the Phantasm implied that The Joker himself was a psychopathic manchild after his transformation. Despite Phantasm's hatred for the Joker, when he's finally caught at the climax, there's a moments hesitation as Phantams realizes Joker isn't the same ruthless mob hitman from years ago, but just a grinning lunatic, no longer capable of remorse, and motivated only by a desire for personal stimulation through murder.
Batman: The Animated Series has a rather Tear JerkerDeconstruction in "Baby-Doll"; The eponymous supervillainess is a 30 year old actress with a medical condition that causes her to look about five, despite having the emotional and intellectual maturity of her actual age. Because of this, she was never taken seriously beyond her original role in a sitcom and ended up being Driven to Madness, throwing up her Cheerful Child stage persona as a psychological shield against her miserable existence (though it isn't perfect-she slips up and reveals her true, depressive personality on occasion). The plot is driven by her attempt to recreate the show's setting in an attempt to return to the one happy part of her life. Her emotional immaturity is a mask to help her avoid her problems with adulthood, as revealed when she crosses the Despair Event Horizon.
The eponymous character of Invader Zim can edge toward this. His interactions with his leaders, especially.
Zim: My Tallest! My Tallest! My Tallest! My Tallest! My Tallest! It's me! Look at me! My Tallest? My Tallest!
Zim: But I must get my equipment or... I won't... get it.
Squidward from Sponge Bob Square Pants. While most of the time acting serious, often several times behave very childish way, ultimately the childish behavior becomes a dangerous madman. And no doubt, the clearest example for this is in the episode "Fools In April".
Plankton also may count. It was in the early seasons an evil enemy, especially as he is seen in the film, but at least as seen in the episode "FUN", seems to have pretty a childish side with SpongeBob when he befriends him. And it is assumed that Plankton is almost as old as it is Mr. Krabs.
Grimlock from Transformers Generation 1 is a Psychopathic Mech-Proto who regularly tries to defeat Optimus Prime for leadership of the Autobots, destroys Decepticons with pleasure and rules his faction of Dinobots with an iron tail... in his down time, he enjoys fishing with said faction, hearing stories about the Good Ole Days from Kup (in the middle of battles) and giving human children and annoying, rhyming Autobots piggy-back rides. He also has his own brand of Hulk Speak.
Speaking of rhyming Autobots, Wheelie might actually fall into this catagory. He fights about as well as any other Autobot and has taken down robots three times his size, but generally speaks in sing-song rhymes and hangs out with a 12-year-old human boy.
Galvatron in Season 3 definitely fits this trope, from treating potential mass murder as 'sport' and 'hunting season' for Autobots he acts like a child whenever he loses with the Decepticons taking the brunt of his tantrums. They eventually get sick of it and tell his loyal lieutenant Cyclonus to do something about his insanity.
The Warden from Superjail! puts the Manchild in Psychopathic Manchild. He acts his shoe size and is barely sane enough to even keep his emotions together. For example, in the pilot as the Warden sings and pets a dead rabbit, he rips its skin off in a moment of unprovoked aggression, then promptly puts the bloody skin on his head and orders Jared to get bunny suits for the inmates.
The X-Men animated series' rendition of Kevin McTaggert aka Proteus. The cartoon took the character and made him a teenaged mutant with the mind of a young child after being locked away from the world by his mother Moira, due to said powers. He possesses people and mindrapes them while doing so, has minor reality warping power (which work like a charm on none other than Wolverine and reduce him to a borderline blubbering wreck for a while), and does all kinds of terrible things... because he desperately wants to see the father who left the family shortly after his powers manifested. While this is a far cry from the horror version of the character in the comics, it's a Justified Trope since this particular X-Men cartoonwas an animated series geared towards kids and young teens in The Nineties; Proteus wouldn't have fitted in the cast, had his portrayal not toned down.
The Batman's version of the Cluemaster. He was a former game show contestant and he believes he lost because his opponent cheated. He has spent 30 years doing nothing but plot his revenge. In his mothers basement no less.
Tarrlok has shades of this in episode 8. He has a lot of power in Republic City but comes off as a spoiled brat who will do anything to get what he wants and won't listen when others try to reason with him. However, it's much more complicated
Amon/Noatak is ultimately shown to be a this in the finale. He comes across as a naive man who just wanted the good life with his older brother (who happened to be the aforementioned Tarrlok) that their abusive childhood at the hands of their father, Yakone, denied them.
Baron Vain from The Modifyers, the Big Bad who gleefully goes "Yay!" when his favorite agent shows up, to ecstatically feeding incompetent henchmen to a gigantic fish while playing opera music.
Darth Maul shows spades of this in his return in season 4 finale of Star Wars: The Clone Wars. He hides himself from Savage behind boxes and can only be lured out by Mother Talzin's bright, floating energy ball, which he chases after in a way you would expect a small child to. Sure, he gets "better", but the effect is still fairly tragic and quite disturbing.
Senor Senior Junior is a mild form of this trope. At one point when his father told Kim Possible when rescuing a band from the former's clutches, told her that he'll unveil his new toy: a laser turret. Junior then tells Senior that he told him earlier that the turret was not a toy (implying that Junior attempted to play with it), before Senior explained that he meant the term figuratively.
Satan is whiny, insecure and fickle. He doesn't even seem to be that much of a bad guy, and on his good day his domain can be quite nice a place. But he easily falls under bad influence and will launch an invasion against Heaven or Earth at the drop of a hat.
Stan's father Randy Marsh sometimes falls into this category, one such example is from the episode "Night of The Living Homeless" in which he threatens the other townsfolk with a shotgun holding them hostage fearing they could become "one of the homeless" (treated like a zombie plague), he then murders his friend Glen after learning he lost his house, then later acting as if he were still alive.
Shredder's mutant henchmen Bebop and Rocksteady from the 1987 Teenage Mutant Ninja Turtles cartoon were shown to read comic books, watch cartoons, and play video games in their spare time. In general, they also did tend to act very childish.
Eddy's brother from Ed, Edd n Eddy. He's an adult and he still likes to beat up kids, especially his brother Eddy.
Lord Hater in Wander over Yonder who is immature, short tempered, and has a huge obsession of being The Greatest in the All the Galaxy! When Wander challenged him over a trophy he was more interested in winning the trophy, than the planet he already conquered.
Snaptrap in Tuff Puppy who constantly makes evil schemes for petty reasons (like blowing up the sun to make popcorn), acts like a immature dick to his henchmen, and constantly argues with his mom.
Works of fiction targeted towards children tend to make the villain fit this trope (Ironically to make the work more appealing to them).