In episode 20 of Cowboy Bebop, Spike faces off against Mad Pierrot in a creepy circus inspired by the Batman animated series.
It's also called Space Land, and can be seen as a mockery of Bebop itself.
The titular Robot Carnival is one of these. It used to be a normal circus, but years of wear turned it into this and it turns the citizens into the towns it visits into its new performers. Or just makes them explode.
The season 1 finale of Team Galaxy features this, where the circus clowns kidnap humans for their performances.
There were hints of something called a "Nightmare Circus" sub-arc within the Mahorafest arc of Mahou Sensei Negima!. Sadly, it was cancelled due to the main story taking up much more time than expected.
Black Butler has a whole arc in the manga where Ciel and Sebastian join Noah's Circus to investigate the whereabouts of children that have gone missing. Needless to say, what starts off as your average circus with jugglers, tightrope walkers, and acrobats turns much darker as we learn about the secrets behind it.
Near the end of the ultra- squick horror manga Gyo, the protagonist visits a circus where all the acts are composed of or powered by victims of the "death stench" gas-producing virus that has ravaged Japan.
Another short manga by Junji Ito, Circus ga Kita also has a travelling circus where performers die one by one during the show. It doesn't matter that the circus loses performers or that the audience witness these horrors, since every single spectator will become part of it.
In Tite Kubo's short lived Zombie Powder, Balmunk has a Circus of Pain/Fear that just springs up from the ground.
Cat Soup has one, featuring a woman getting dismembered and a giant bird that's swallowed clouds (that ends up causing a flood).
Copernicus Breathing may or may not fit neatly into this trope. Although it does not contain any supernatural elements, le Cirque de Soir is pretty gritty and the way it is visually portrayed is like a horrifying acid trip for a vast majority of the time and not to mention, the ringmaster pimps out several of the performers.
In the Marvel Universe, the Circus of Crime was a front for criminal activity. It consisted of guys like Bruto the Strongman, Princess Python, the Human Cannonball, the Great Gambonnos, the Clown, Live Wire, and the variously threatening-and-not so much Ringmaster, whose hypnotic hat was often the key to his schemes. Generally less overtly creepy and homicidal than other examples of this trope, the Circus of Crime is mostly in it for the money.
Marvel villain Arcade's deadly amusement park, Murderworld, also has elements of the Circus Of Fear, and so far hasn't fallen to Villain Decay. Probably because he has so many Murderworlds.
Also in the Marvel Universe, in a New Mutants flashback, they find a circus, it's run by Skrulls who are kidnapping humans and shrinking them. As expected, the New Mutants trash the place, including various structures that didn't need it.
Slapstick, another Marvel hero resurrected in the aftermath of the Civil War, got his start trying to save his classmates from Evil Clowns From Dimension X who were using a circus to kidnap people and turn them mediocre. No, really. Everything got righteously smashed up.
The Joker likes doing variations of this in the various Batman incarnations. Most famously, he buys an Amusement Park of Doom in The Killing Joke and crews it with circus freaks, using it to attempt to drive Commissioner Gordon insane by showing him naked pictures he'd taken of Gordon's daughter after he shot her through the spine. And there was a song.
Also from Batman, in Grant Morrison's Batman and Robin, the first arc features an evil circus troupe led by the Nightmare Fuel inducing Professor Pyg. In the second issue, the new Robin visits the actual circus and more Nightmare Fuel starts when he is attacked by Professor Pyg's masked henchmen.
Pyg's major underlings all resemble sideshow freaks, as well, including a grossly overweight bearded lady in a tutu and a human flame act who can burn others but not himself.
In Spider-Man: Noir, Norman "The Goblin" Osborn recruited his inner circle from the circus freak show. The Vulture was a geek who had become more animal than man, Kraven was an animal tamer, the Chameleon had the uncanny ability to alter his facial features, Ox was a strongman, Montana did rope tricks, and Fancy Dan was a promoter. As it turns out, Norman himself was a refugee from the same freak-show, where he had been put on display since childhood as "the Goblin" because of his thick, green, scaly skin. He hides it under a latex mask nowadays.
The Real Ghostbusters fought a ghost-circus in their comic-book incarnation. The zombie elephants were somewhat creepy.
The second arc in the first volume of I Hunt Monsters has the heroes dealing with a circus run by werewolves.
An early arc of James Robinson's Starman features this type of circus. The "freaks" themselves are mostly nice people, but they are controlled by the ringmaster and his evil lieutenant. Because this is Starman, the lieutenant comes back during the invasion of Opal City.
Hoax Hunters has a traveling circus as a front for a murderous cult. It used to just be a regular circus, until the ringleader met an Eldritch Abomination and went insane. Most people who come in contact with it never suspect there's anything wrong — and also probably think that goat guy is wearing a costume.
Akiko's horrific past as a Magical Girl in the backstory of the Battle Fantasia Project involved three years fighting against the Carnival of Blood, who want you to join them forever, in addition to the four years fighting her current enemy, the Nightmare Factory. It's primarily glossed over if mentioned at all, because going into specifics would subject the poor girl to horrors that would break most Magical Girls, horrors to which not even Puella Magi Madoka Magica can compare.
In the Horseshoes and Hand Grenades sidestory Month of Sundays, Damballa transforms the Narumi Detective Agency into this and the main attractions just happen to be the fighting of Creepy Doll versions of three different Kamen Riders.
Invoked in Disney's Pinocchio where some of the crates the Coachman locked about half the Donkey Boys in appear to be heading for a circus (the other crates were heading for the salt mines).
Films — Live-Action
The film Batman Returns had the Penguin secretly running the Red Triangle Circus Gang, a gang of crooks who, like him, were former circus performers. It is hinted that they abducted children when they were a legit circus, likely the reason they shut down.
Two-Face's goons dressed up as two-sided clowns when they attacked the circus in Batman Forever.
Oddly enough, this has been mostly averted with The Joker in his most recent live action outings—though he does come close in Batman
The movie Freaks both used and defied this trope. The freaks are all loving and caring people, the clowns are good-natured and charming (although one of them has a hilarious speech-impediment), and the animal trainer is frigging gorgeous. There's a bit of black comedy involving a pair of conjoined twins, one of who is getting married, and the soundtrack is slightly creepy, but that's about it. Unless you get them angry, as the evil female trapeze artist and misogynistic strong man do. Do NOT get the freaks angry.
The movie version of The Elephant Man involves the title character's escape from one of these. The movie was directed by David Lynch, who must have jumped at the chance to try his hand at this trope.
No prizes for guessing what the Hammer horror film Vampire Circus is about.
In the James Bond film Octopussy, the titular female lead uses a circus as a cover for her criminal activities as well as using circus acrobats and aerialists to commit crimes for her, while a renegade Soviet general plants a nuke in her circus. Not necessarily evil, but initially misguided.
The 1968 British horror film Berserk starring Joan Crawford and Michael Gough is set in a circus where there are a series of gruesome and unexplained murders.
Give Yourself Goosebumps #1 is called Escape from the Carnival of Horrors. And then much later there came "Return to the Carnival of Horrors", because apparently you just can't stay away. (To be fair you're bullied into it by the book itself in the first entry (after all what the point of reading it). In the second entry you brave it once again to get your oblivious cousin out.)
Endless Quest also had an entry actually titled Circus of Fear. Decide for yourself whether the title's talking about the circus being run by bad guys or all the usual circus animals and attractions being replaced by creatures from the D&D bestiary.
Averted/inverted in Iain Lawrence's Ghost Boy. The main character discovers that the freaks are kind and good-natured, but they still unsettle him a little, and the non-freaks are much better at being charming.
Angela Carter's Nights at the Circus doesn't feature an evil circus per se, but some scary and strange crap definitely goes down.
One of TSR's Endless Quest books was actually called Circus of Fear, involving a circus run by evil dopplegangers looking to assassinate the current ruler and take over the kingdom.
In several Incarnations of Immortality books, ghosts run an ethereal amusement park, where the ghosts try, and often succeed, in scaring the visitors. Amusingly, people kissing seems to scare the ghosts, in return. However, the rest of the amusement park is typical, if ghostly, fare such as a smoke ring toss.
Subverted in The Saga of Darren Shan, where the "Cirque Du Freak", though intended to be nightmarish and slightly horrifying (and potentially dangerous), actually provides a warning beforehand of what it will be like, and gives patrons an opportunity to leave. If any are injured, the show is halted until they are fixed up. Also, the "freaks" are rather friendly and personable people, and the Circusmaster, Mr. Tall, actually runs the cirque as a means of providing people with strange abilities with shelter, family, the opportunity to travel, and a circumstance where their unique abilities can inspire wonder rather than fear.
The Pilo Family Circus. An extradimensional travelling circus of madmen, magicians, and monsters, where the employees are paid in bags of management-controlled wishing powder made from the crystalised remains of human souls- extracted from the audience. Oh, and the managers have a nasty habit of causing global chaos on Earth via the Fortune Teller and the Clown division, on behalf of a race of reptilian demigods imprisoned beneath the showgrounds.
Redwall's Slagar the Cruel runs a traveling show which seems perfectly benign (except that all the performers are weasels and stoats). The show is used to distract the good guys while a performer drugs their drinks and Slagar himself hypnotises them, and when they wake up the "show" has vanished, taking their children with it.
Count Otto Black, a Running Gag recurring villain in Robert Rankin's insane versions of novels, is often seen running a circus.
Jean-Claude, from the Anita Blake series, owns and runs a fully functioning vampire circus, clowns with fangs and all.
The Theater des Vampires in The Vampire Chronicles, who are vampires hiding in plain sight. They manage to be both scary and complete jackasses at the same time. They act out vampires killing humans on stage while the human audience watches in oblivious entertainment, and sometimes even satirically offer themselves in place of the victim they don't believe is a victim.
Not a circus, but an amusement park - Full Tilt by Neil Shusterman. Good god, Full Tilt.
The Buffy the Vampire Slayer novel, 'Circus Of Souls'. She figures it out soon enough, but is then zapped by the brain-altering magics of the circus.
The setting for the Ravenloft novel Carnival of Fear.
According to the short story "A Boy and His Monster" in Star Wars: Tales from Jabba's Palace, Malakili the Rancor Keeper was previously employed by the Circus Horrificus, where Hutts paid to see weird creatures get tortured to death.
There's a G-rated version in the children's picture book The Amazing Spider-Man: The Big Top Mystery. To be sure, the circus in itself isn't scary, but it becomes this way once Spidey learns that he has to stop a saboteur from causing deadly "accidents" for the performers and spectators. Among the perils are a panicky elephant, a crazed lion, and a murderous clown who had "arranged" all the accidents and whom Spider-Man had rescued from the aforementioned lionearlier in the story. After he is finally caught, arrested, and questioned, the clown admits that he wanted to prevent the owner from selling the circus so he wouldn't lose his job.
The Fun Fair, Nightside's first amusement park ended up this way. It's considered a very bad place (and this is Nightside we're talking about) and requires services of major exorcists just to keep it quiet. The protagonist even comments on the nerve and bravery of someone who graffittied the front gate sign.
Circus of the Dead, a short e-book by Seth Blackburn, is about a circus that features a real zombie as it's main attraction. As is expected, things don't end well.
The Goosebumps book Welcome to Horrorland, which spawned a sequel (Return to Horrorland) and two spinoff series (Goosebumps: HorrorLand and Goosebumps: Hall of Horrors).
There was also an untelevised script for a Sixth Doctor story called The Nightmare Fair, later released as a novel, then an audio play (unofficial) and then an audio drama (official). The circus in question belongs to an enemy called the Celestial Toymaker.
Torchwood series 2 had the Night Travellers in the episode "From Out of the Rain".
Papa Lazarou's circus in The League of Gentlemen might qualify as a subversion. While Papa Lazarou's appearance is pure Nightmare Fuel and he spends all his spare time kidnapping women ("You're my wife now!") Royston Vasey is already so full of freaks that the circus soon flees in terror, as the town is too weird even for them.
Heroes headed in this direction in their final season. The season opened with the role of primary antagonists falling on a group of carnies, led by a man named Samuel who injected ink into people and manipulated it inside their bodies along with creating earthquakes and manipulating earth In the end it turns out this is a subverted trope as the carnival was a protected home for people with powers where they could openly be themselves.
Most of the carnies aren't really evil, just misguided by Samuel. He was manipulating them to give him more power. The carnies were just looking for an safe haven to openly use their abilities and earn a living.
An episode of Mutant X dealt with a travelling circus led by a man whose power was to trap people inside funhouse mirrors.
The short lived series She-Wolf of London (aka Love & Curses) featured an episode during it's first season, Big Top She-Wolf, that dealt with a demonic circus.
A lot of Tom Waits' stuff, especially the albums Swordfishtrombones, Frank's Wild Years, Rain Dogs, Alice (which includes a song about Johnny Eck), The Black Rider, and Blood Money.
"Circus of Death," from the Human League's first album Reproductions, tells the story of a singularly destructive circus. The song is also, oddly enough, a Hawaii Five-OFanfic of sorts.
The Insane Clown Posse's appearance and Dark Carnival mythos is based on this trope. Many of their songs, including "Murder Go Round", "House of Mirrors", "Halls of Illusion" and "Tilt-a-Whirl" relate to Circus, or rather, Carnival of Fear-based themes.
The cover art, title track and its music video, and associated merchandise (comic books, action figures and a CD-ROM game) of the 1998 KISS album Psycho Circus make use of this concept.
This is kind of the whole schtick of Seattle-based group Circus Contraption, especially during their "Grand American Traveling Dime Museum" show.
Come inside, for the ride, Your deepest, darkest fear! The best night, of your life, You're never leaving here! The unknown, the unseen, Is what you'r gonna find! Witness this, witness that, Untill you lose your mind!
"Circus Apocalypse" by the dark cabaret act, Vermillion Lies.
Come down and join the circus It's the end of your world Come down and join the circus All you dead boys and girls If you still have a pulse We can remedy that You can check your life While you check your hat
In the 2013 Broadway revival of Pippin, the Show Within a Show "Pippin, His Life and Times" is specifically being performed by a circus troupe (with performers from the Real Life Canadian troupe Les 7 Doigts de la Main). The reason it's this trope is that over the course of the production, particularly in the second act, matters become increasingly disturbing until the Grand Finale - where the players try to convince Pippin to commit a dramatic suicide in order to be "Extraordinary". When he refuses, the Lead Player becomes hostile and takes away the "magical illusions" of the show and he and the company encourage members of the audience to come and take Pippin's place. Because "we're right inside in your heads!".
The Swords & Sorcery Scarred Lands setting has a Circus of Fear nation. The Carnival of Tears in Blood Bayou.
Appearing in the Warhammer spinoff game Mordheim, and referenced in Warhammer too, is the Carnival of Chaos, a circus staffed by Chaos worshippers and daemons of Nurgle (who, despite being the Chaos God of despair, is a rather jovial fellow). The show seems to be benign until the climax when the Carnival members and and their stage's true putrid corruption is revealed. At this point the entertainers slaughter anyone who hasn't already fallen to the diseases secretly spread during the performance. They then round up the women and children who survived, the Carnival Master taking a finger from each woman and taking them as his "wives".
The titular organisation from Ravenloft's Carnival box set seems like this at first, with the workers divided roughly between mutated freaks and spooky, utterly silent folks in bizarre face paint, many of which work as rather disturbing clowns, but it actually subverts the trope. The Carnival is one of the most accepting and hospitable places in the Demiplane of Dread, and most of the workers are good people. Most of them... there are some members who are actually evil, though they've managed to hide this from their fellows. One of the options for the true nature of Isolde, their leader, (and which has more or less been adopted as the truth), is that she's a rogue angel who came to Ravenloft to pursue the incubus known as the Gentleman Caller, with the Twisting resulting from the interaction between her nature and the sheer corrupt nature of Ravenloft. The original workers for Isolade's Carnival, however, are escapees from a now-dead Darklord called "The Puppetmaster", who ruled a domain (the Carnival l'Morai) that played this trope straight (Carnival of Fear, mentioned in Literature above, deals with the original domain, not the current Carnival).
Despite all this, as is only appropriate in Ravenloft, the Carnival's still very creepy. The Skurra are attendant Vistani who wear strange black and white facepaint (the Skurra-verra) that protects them from the Twisting at the cost of making them mute. The Twisting causes people who stay overlong in the Carnival to mutate, their form changing to reflect their hearts and souls- for example, the bitter and malevolent Professor Pacali's repressed plots take life as deformed midget "things" that grow from his flesh. This is the source of his "Pickled Punks". One of the "attractions" are the horrifically warped Chaos Spawn-like remnants of people who attacked the Carnival, entities referred to simply as The Abominations. And some of the populace were strange and unnatural before they entered the Carnival, like a bloodthirsty leopard with the ability to assume a humanoid form, a Seawolf (an amphibious werewolf), the Fetch of an evil wizard and a Wax Golem.
1st edition supplement Adventure Pack I, adventure "The Circus of Gandolfo". The title circus is just a cover for a Doctor Frankenstein-like Mad Scientist who likes to kidnap people and perform bizarre experiments on them.
An Old World of Darkness supplement titled Midnight Circus detailed something very much like this, containing all manner of supernatural creatures enslaved to a mystic travelling circus dating back to the Roman era. It was disturbing even by World of Darkness standards.
In the New World of Darkness, Vampire: The Requiem gives us the vampiric bloodline called the Carnival. Every last vampire of the bloodline bears a circus-freak deformity (their founder suffered from sirenalia, and was billed as "the Andalusian Mermaid"), and they often act as traveling or static carnivals, the better to hide in plain sight.
The Pathfinder module Carnival of Tears showcases a carnival where icy fey have taken over, and are slaughtering the attending townsfolk in gruesomely creative ways. No one notices, due to powerful illusion magic that replaces every event of horror with a completely normal, even enjoyable, carnival scene.
One of the playable "families" in the card game Gloom is Darius Dark's Den of Deformity. One of the characters is a scary clown with a skull-like face. The description for Darius Dark himself is: "The circus is in Darius' blood. And there is an awful lot of blood in Darius' circus."
The yearly summer sideshow event in Killing Floor turns all the specimens into circus-themed versions of themselves. For instance, the flesh pound becomes the flesh clown, and the patriarch becomes a ringmaster. There is also a map made for said event called "Abusement Park."
The higher levels of play in the MMORPG City of Heroes include a "Circus of Fear"-style villain group called the Carnival of Shadows.
The members of the Carnival feed on their patrons' souls.
At the end of the game Psychonauts, Raz (the protagonist) accidentally merges his mindscape with the villain's. Since Raz grew up in the circus, his mind is molded to resemble a giant circus tent. However, the Big Bad has a mindscape that reflects how traumatized he was when his father, a butcher, would slaughter and cook his rabbits. So, what do you get when the two minds collide? A horrible, twisted circus where nearly everything is made of meat.
Raz: My memories were bad enough. This is just gross.
Raz' remark above implies that his own (real, not that dream he had because Sasha had to go and buy the cheap Brain Tumbler) mindscape wouldn't be so much fun to begin with. He gains new perspective on his old memories at the end of the game, though, which leads me to wonder what it might look like now.
The first Shining Force game for the Genesis had a circus-based level, with a powerful marionette heading up the attacking forces (clowns included).
Okay, so it's a carnival, but Tokkentakker's little three-ring terror ride that is the basis of Carn Evil certainly fits the bill, complete with demonic floating clown head.
The theme park from Silent Hill 3 is the Dark Silent Hill version of a theme park. Come for the faceless fairytale characters, stay for the hooded, twitching carousel flesh-horses and dark echoes of previous lives!
Lakeside Amusement Park is actually first visited near the end of Silent Hill 1, and also features a bloody battle on the carousel, this time with Possessed Cybil.
And the second stage too. Sure, it may not be dark anymore, but that's a pretty messed up funhouse you have to go through.
The Nation of Fools from Castlevania: Portrait of Ruin. Enemy types include demonic clowns and evil acrobats. The circus appears to be in some post apocalyptic world surrounding a black hole. At the end of the level, the black hole turns out to be the level boss Legion.
The creepy mock-circus music just to drive the point home.
LeChuck converts a part of Monkey Island into an amusement park of doom (the "Carnival of the Damned") in The Curse of Monkey Island as part of his master scheme: Reasoning that the first thing a sailor wants when he arrives to port is a family-oriented fun-park, he builds the Carnival of the Damned, and its centerpiece ride, the Rollercoaster of Death, leads straight into Big Whoop and converts everyone who boards the ride into a ghost pirate minion.
EarthBound has this in the city of Threed. It already starts off with a scary circus and a town overrun with undead/spectral monsters. The trope is inverted at first, as the big top is the sanctuary for townspeople. When another circus tent mysteriously shows up, the trope is played with a Nightmare Fuel-inducing variation, as the tent itself is a monster.
The aptly named Wonky Circus in Wario World. There's also the circus setting for the third boss (Chortlebot) in Wario Land: The Shake Dimension, although it's only ever used as a battle arena against said Monster Clown.
Take your average Circus Of Fear, add in untold volumes of molten rock for all the geothermal power you'll ever need, have the whole thing built in a week due to harnessing the powers of a monster, and staff it with robots out the ass. Welcome to Eggmanland. Enjoy your stay.
"You ever been to a carnival? You know that game they have with the water guns and they're shooting water into these clowns' mouths and there's a water balloon that inflates and inflates, eventually it explodes, everybody's happy, whoever won the race gets a prize from, you know, the carny who's got, like, three thumbs on both hands, you know what I'm talking about? Well, that's basically this level. Except for the part where everybody's happy. This level's hard."
The Legend of Zelda: Majora's Mask has a giant music box that plays what can only described as scary circus music. It doesn't even help much that it also scares the mummies away.
It actually makes it worse: music that is so bad that even the undead can't stand to hear it.
Ape Escape takes this trope and packs every element into the first half of the first game's monstrously huge Very Definitely Final Dungeon. The main area is an amusement park taken over by the Big Bad, with lots of separate areas branching off, including a crazy mine cart style roller coaster, and a more literal circus flavored area, where you must defeat an evil clown. The other sections are mostly other common video game settings, including Wild Wild West and a Big Boo's Haunt. This is only the first half of the level. The other, even longer, half is the Big Bad's flying castle, which includes elements of Tomorrowland. Yeah, this series really likes its location tropes.
Blood's "Dark Carnival" in the first episode is supremely twisted. Aside from a lantern-carrying statue of Death siccing zombies on you when you ignore his request for a ticket, the optional game where you kick a severed head through a slowly opening and closing mouth to win a prize, or the secret funhouse level that shoves rotting skeletons at you while maniacal laughter plays, there's also the fact that the whole place is built next to an evil temple filled with cultists who want you dead. Well, deader.
The second Soviet mission of Red Alert 3 which takes place in a vagrant carnival built on an abandoned rocket test site. It seems sparsely populated until the Soviets activate the abandoned launch facility upon which Japanese troops (including a Psychic Commando) burst out of the tents and surround the Soviets. The actual mission itself is called something along the lines of "Carnival of Hatred".
The first level of Dark Chronicle had one of these coming to Max's town, which culminated in a boss fight against the deranged clown Ringmaster and his pet elephant, Linda. And then he chases you onto a train and throws bombs at you until the whole train derails.
Marvel Ultimate Alliance has a level in Murderworld, mentioned in the Comics section. Complete with kamikaze bots, android copies of party members, and clowns with radioactive flower-squirts.
In World of Warcraft, the Darkmoon Faire is a recurring event, and definitely qualifies for this trope. It is most assuredly not a wholesome thing; much of the staff is undead, the colours are flatly ugly, the designs on the tents are disturbing, and then there are the quests.
With patch 4.3, it get's even creepier, as you now go to Darkmoon Island. When you enter the portal, you end up in a very ominous forest with gnarled, apparently dead trees. The signs that point you to the fair mention "ignoring the eyes" in the forest. There was some mention of never wandering too far into the woods... And if you decide to look around you might find some cages filled with humanoid skeletons, and a forsaken woman selling some ratherquestionablemeatproducts.
Then there's that all-seeing eye at the entry gate that looks a lot like it belongs to one of the raid bosses... and the NPC who stumbles over his words as he almost says that the Master would be interested in certain items. It is very heavily implied that the Faire is related to the Big Bad of that expansion.
Painkiller:Battle out of Hell has a circus/ fun fair called Loony Park with killer clowns and monsters made out of snack food.
Ryan Amusements in BioShock's Rapture is designed mostly as a propaganda device to scare children into never going to the surface.
One level in ASC's Sanitarium has this. It's a delusion...
Sweet Tooth's circus in Twisted Metal 4 features such attractions as the "roller toaster", aside from being a battleground where the demented clown and a number of assorted psychos try to kill each other.
The downloadable Loontrack in POD featured deformed fairytale castles, giant roulette wheels, an enormous wizard hat and rusted metal plates, located on a planet infested by an alien virus. Or is it? When you look over the guardrails, there is only a black void there...
Stage 6 in Silent Assault, complete with a Monster Clown head for a boss.
Baldur's Gate II: The circus in Waukeen's Promenade starts out normal — until their disgruntled illusionist Kalah uses powers gained from some kind of an implied Deal with the Devil to turn the inside of the tent into a weird personal world of his own that is Bigger on the Inside and that no-one can escape until he is defeated.
In the Spider-Man game for Sega Genesis, the Green Goblin takes over Coney Island in the second level, and you have to fight your way into the fun house to capture him. The music on the soundtrack is very Danny Elfman-like, creepy and catchy, and among the Mooks you have to mop up are strong men, fire-breathers, and armless cobra people(!).
Mystery Case Files sets two of its games, Madame Fate and Fate's Carnival, in the titular Madame Fate's Carnival. The detective is tasked to investigate the death of Madame Fate herself and a curse that's engulfed her carnival.
Mort from Gunnerkrigg Court creates one of these at Antimony's suggestion to scare her classmate Paz.
Gamzee from Homestuck more or less has this as his overall intention now that he's "sane", a turn of events which could arguably be the most utterly terrifying moment in the comic to date. Just listen to "Midnight Calliope" or "The Carnival". It's recommended you have a spare pair of pants on hand.
It has been announced that once Grave Academy starts, a part of the academy or a separate location will be this.
An episode of the Flash series Xombie had Dirge and Zoe fighting a horde of zombie clowns in an abandoned amusement park, while Dirge's undead dog CerebusCerberus faced off against a zombie tiger.
A Captain Caveman episode on The Flintstone Comedy Show, "Clownfoot," featured the episode's villainous clown, Clownfoot, using a circus as his hideout. At said circus, Clownfoot also rigs a tandem bicycle Wilma and Betty are riding on a high-wire to fall apart, over a cage full of hungry saber-tooth tigers.
The Tiny Toons episode "Sawdust and Toonsil" has Gogo Dodo caught and imprisoned by a very-Satanic-looking ringmaster when he attempts to rescue some of his fellow Wackyland residents (a sphinx, a unicorn, etc.) from a circus. Bugs, Buster, and Plucky have to rescue him. They never really show the rest of the circus, but the Ringmaster's treatment of the Wackylanders is pretty nightmare-inducing.
Mighty Max has an episode where an Evil clown named Freeko kidnaps children, and morphs them into creatures for his freakshow. This episode, as one would expect, is brimming with horror
The Funhouse in ReBoot. One of the rarest games on the Net (because only User children play it) and is nearly impossible for sprites to beat. Bob and Dot are the only confirmed sprites to escape it alive.
In Aqua Teen Hunger Force episode, "Circus," Shake sells Meatwad to the circus for $2. Other acts include "Inside-out Boy," and the show does not go well for anyone, especially the audience.
Carnival Diablo: The Ultimate Sideshow plays on this trope. The Carnival is run by the Devil, and the performers are presented as other-worldly beings with bizarre abilities. Many acts seem to put performers, and sometimes audience members, in danger.
The Circus of Horrors is a real circus show that plays on the trope.
The original Roman-style circus (gladiator fights to the death and Christians being fed to wild animals), making this trope Older Than Feudalism. However, the "attractions" were only scary to the people in the pit as most Romans enjoyed these public displays of violence.
Circus Circus in Las Vegas used to have a 3D motion ride with this trope as its theme.