Killer Klowns from Outer Space suggests that the very presence of clowns and circuses in Earth culture is a warped memory of an ancient visitation by inimical aliens.
Pennywise the Dancing Clown from the 1990 adaptation of Stephen King's book IT, portrayed by Tim Curry. Even the on-set cast and crew were terrified. Even scarier when you realize he's actually an Eldritch Abomination disguised as a clown. Ironically, he chose the clown form to trick children into trusting him.
Pennywise from the 2017 adaptation It (2017) and It: Chapter Two is even more monstrous and frightening, with Bill Skarsgard taking Its sadism and predatory nature Up to Eleven because in this version it gets off on using the clown's creepy Uncanny Valley-ness to make its victims even more terrified so it can feed off their fear. Even when it's trying to pretend to be a nice clown it immediately makes its victims unsettled, and even has to play to one victim's empathy by crying because "he's a creepy clown who nobody wants to be friends with" before she'll come within range to be torn apart.
In Poltergeist, towards the end a toy clown is possessed by evil spirits and ends up attacking the older brother. This was foreshadowed earlier in the movie when the boy covered up the clown with his jacket, because it was staring at him when he went to bed.
Clown Doll: PEEK-A-BOO! HAHAHAHAHAHA![grabbing Ray by the throat and dragging him under the bed] You wanna come play? Come on, let's play! This is a fun game, huh?! ..... Hey, what are you doing?! Ray: Uncle Ray-Ray's got a game... Clown Doll: Hey get your finger outta there! Ray: Tickle tickle tickle tickle tickle! Clown Doll:AAAHHHH!! AAAHHHH!! Ray: You wanna play with Uncle Ray?! Peek-a-boo! [grabbing the clown by the throat with his penis and dragging him under the bed] Clown Doll:AAAHHHH!! AAAHHHH!! HELP! AAAHHH! Oh, GOD! Ray: Here's a little balloon animal! Da, da, da, da, da, da, da, da, da! [SQUISH!] Clown Doll: OOOOOOOOOOOOHHHHHHH!!!!!!!
The Greatest Show on Earth features a gentle, altruistic, medically-inclined clown who never removes his makeup, even off-duty... because he's on the run for the murder of his wife. Possibly a subversion, as it was a Mercy Kill (albeit still illegal).
Subverted in The Chase: Charlie Sheen's character Jack Hammond is pegged for a felony because he works part-time as a clown, despite the fact that he was innocent. (He's convicted, however, because a crucial piece of evidence was deemed inadmissible, which led to the events of the titular car chase.)
John Candy starred in a drama/horror film in the '70s titled The Clown Murders which was about a Halloween prank gone wrong. The main enemy was a guy in a clown mask but he only appears for a few seconds in the movie.
In Diary of the Dead (the Romero Zombie movie) there's a Zombie-Clown at a birthday party and he bites the birthday child's dad's ear off. It's hilarious and absolutely terrifying. It's telling that the child is shown to be instinctively afraid of the clown.
And in Day of the Dead (1985), too. It makes you wonder just how quickly the Zombie Apocalypse struck that the poor bastards didn't even have time to change into something more dignified for their trip to the hereafter.
Quick Change: Bill Murray's character dresses up as a clown to rob a bank. He's not really evil, though he did endanger the customers and bank personnel (who could have been wounded or killed during the robbery if someone had gotten heroic or the police had charged in guns a' blazing).
Gacy, To Catch a Killer and Dear Mr. Gacy, all about John Wayne Gacy.
An original plan for Halloween (1978) was to have Michael Myers wear a Weary Willie mask instead of the tweaked William Shatner one they ended up using. Michael does wear the clown mask for the film's opening scene, where he murders his older sister.
The Saw franchise has Billy, the grotesque puppet Jigsaw uses to communicate with his victims. He has a white face, oversized smile, swirls on his cheeks and blood-red eyes. His clownish design deliberately contrasts the gritty, metal-and-rust aesthetic of the films, making him even more unnerving.
"The master and I are going to have words. He knows I hate clowns. God, I hate them. I hate them all. I hate Bozo, Ronald, Chuckles with their freakin' dumb noses and their lousy party hats!" - Violator from Spawn, though his hatred comes from the fact that he has to look like a clown.
The first segment of Amusement features a room filled with scary clown dolls and toys. Except one of them isn't...
In Night of the Demon (1957), Crowley-esque cult leader Julian Karswell, who will blithely send critics to a horrible doom, holds children's parties at his estate, playing a magician/clown...pretty benign for this trope, but capable of bad stuff (and in the original story, quick to scare the daylights out of the kids).
The second dream sequence in Pee-wee's Big Adventure is loaded with them. The scariest one probably being the surgeon, who is only revealed to be a monster clown after he pulls down his surgical mask showing his eerily painted mouth. Definitely a case of less is more.
Then there's that motorized clown dummy Pee-Wee chained his bike to...when he comes back and the bike's gone the clown has an evil grin and laughs mockingly!
The various film incarnations of The Joker are classic examples.
The Dark Knight's Joker, complete with a Glasgow Smile; small children will no doubt be quietly wetting themselves in theaters around the world.
In Batman (1989), the Joker and his men also dress up as mimes in order to get close enough to a mob target to kill him, then blast the street with tommy guns.
Joker (2019) focuses on the character and his backstory. In this version, the Joker, or Arthur Fleck, actually starts out as a Non-Ironic Clown of sorts, but as his sanity slips and he starts committing acts of violence, he eventually (unwittingly) forms a group of clown-mask-wearing violent protestors.
In Batman Returns, the Penguin was the leader of the Red Triangle Circus Gang, a group of criminals made up of former circus performers, including several clowns. Likely the nastiest one (called "The Terrifying Clown" in the credits) was the one with the stun gun that threatened Selena in the battle at the tree lighting ceremony at the beginning.
The 2007 movie Drive-Thru features a serial killing clown named Horny.
In Let's Visit The World of the Future, the future is ruled by evil clowns.
The movie Torment features the evil Dissecto the Clown.
In Clownhouse, three mental patients dress as clowns and go on a killing spree.
In the 1998 film The Clown at Midnight, a murderous clown attacks several teenagers.
Uncle Buck had "Pooter the Clown", who showed up to entertain children at a young Macaulay Culkin's birthday party, while drunk, but ends up trying to pick a fight with John Candy instead.
Shakes the Clown is a comedy that treats clowns as a minority. Most of the characters have foul mouths and substance abuse problems, but one clown in particular, played by Tom Kenny, loses it at the end, and holds a woman hostage.
The Family Jewels is a vanity-piece movie for Jerry Lewis, starring in seven roles, including a professional clown who, off the clock, has only contempt for the "squealing brats" he entertains.
The short Québécois film, Le Queloune, rather subverts this. The clown in question happens to be a confused zombie in a clown costume just rising from the grave, and you can't help but root for the poor fellow when it takes him two days to get himself out of his grave site. Then he wanders into a couple's home and scares the wife into accidentally killing herself by falling down the stairs (and when he accidentally himself falls on her corpse, his zombie cravings awaken when he tastes human flesh for the first time). After killing the husband with a shovel (and serving their flesh on a skillet for his first breakfast), he removes his old clown clothes and makeup, dresses himself up in a new pair, and walks out of the house ready to begin a new day as a flesh-eating zombie (unaware that everyone around him outside apparently has thought the same thing, what being zombies themselves and all).
People from Quebec have a fondness for the trope, it seems; not only were Le Queloune and Happy Meal (the vampire Ronald McDonald short above) made there, there's also Pogo et ses amis (Pogo and friends), a stop-motion short about the darkly funny day-to-day life of Pogo the clown (see the Real Life section below) and his friends Ed,Albert and Mr. Z. Even funnier/more disturbing because Ed and Albert are voiced by the same voice actors who do Ned Flanders and Mister Burns, respectively, in the Quebec-made French translation of The Simpsons.
And Pogo is Homer himself.
The 2008 Slasher MovieAmusement. While not a monster clown, the clown wearing psychopath still proves that sometimes you don't have to be supernatural to be scary.
Killjoy and its sequels feature a killer spirit in the form of a clown who attacks campers who disturb his resting place.
S.I.C.K. Serial Insane Clown Killer features a killer who dresses in a clown suit.
Out of the Dark features a killer who targets sex-line workers while wearing a clown mask.
The Spanish film The Last Circus has two insane, grotesquely disfigured clowns battling each other.
Shivers the Clown from the Fear of Clowns duology.
Blue Velvet: Roy Orbison's "In Dreams" or "CANDY COLORED CLOWN!!!" is a Monster Clown in the form of a song. Interestingly enough, Dean Stockwell, who lip-synchs the song while wearing white make up and exotic clothing, comes across as a Monster Clown Pimp.
Shows up again in Inland Empire. The scene with the movie's first big Jump Scare — in which Laura Dern's slightly distorted face suddenly races up to the camera with a Scare Chord — fades in from a creepy painting of a clown. The famous Nightmare Face near the end is also extremely distorted to look like that of a clown. May be related to what Lynch calls the "suffocating rubber clown suit of negativity".
Klown Kamp Massacre and 100 Tears both feature killers dressed as Monster Clowns.
La Casa 3 has the clown doll that Henriette carries around. On few occasions it turns into sharptoothed version of itself.
In the Problem Child series, it's a Running Gag that Junior really hates clowns — although it appears to stem more from intense dislike than fear.
The killer in the slasher/porno hybrid Camp Cuddly Pines Powertool Massacre is a rather badass looking example of this. He was set on fire while wearing a clown mask, and it melted to his face.
In the James Bond movie Moonraker, when the villains big scary henchman Jaws stalks Manuela in a dark alley during the Rio de Janeiro Carnival, he is dressed as a giant clown.
The high priest who conducts the gory temple ceremony for the god Kukulkan in Mel Gibson's Apocalypto could be considered a pre-Columbian version of this trope. His eye makeup looks very much like that of a clown, he laughs constantly, his ceremony is circus-like entertainment for the crowds watching below, and his voice is wild and high-pitched, especially compared to the subdued tone of voice spoken by all the other movie characters (including the other villains).
Eli Roth's film Clown posits that the ordinary Non-Ironic Clown is actually a bastardization of a creature in Scandinavian folklore which lures children into its cave and eats them. ...Oh, and whoever puts on an old Icelandic "Cløyne" suit to entertain at children's parties transforms into the monster.
In Silent Hill: Revelation 3D, Heather is having visions courtesy of her evil twin Alessa. A birthday party attended by clowns with balloons becomes a hideous gorefest before her eyes.
Thomas is taken to a Circus of Fear featuring these in Imaginaerum, who as part of their act begin to scoop his memories away - only his memory of going to the circus with his daughter and feeling like a good parent stops them.
There's also the titular character of the 2013 horror comedy Gingerclown (yet another killer clown played by Tim Curry), who leads a group of monsters that inhabit an abandoned amusement park that a group of high school kids happen to explore one night. It goes like you'd expect.
The 1994 British horror/black comedy Funny Man features the titular demon, who takes the form of a twisted, homicidal, wisecracking harlequin. Imagine "Freddy Krueger meets the Joker," and you have a solid grasp of the Funny Man.
In Parker numerous bad guys dress up in clown get up and Uncanny Valley Makeup when terrorizing people with guns and starting fires.
One of the Christmas-themed monsters in Krampus is an all-devouring toy jester.
Inverted in Billy Madison where the clown in question seems innocent enough, but when he is subject to a head injury that leaves him unconscious and drooling blood, everyone else seems oblivious to the seriousness of the situation as they laugh at him.