When it comes to cretinous comic book villains, the Joker seems to be the King of Unsettling Monsters. But he's got nothing on some of Marvel's creepiest creeps. Look at someone like the humungously obese tyrant Mojo, ruler of (you guessed it) Mojoworld. Between the robot spider legs he clacks around, the yellow needle teeth and the torture hooks that keep his fat face from smooshing his eyes shut, Mojo is a living nightmare. And that's just the body-shaming.
Mojo is also the sole ruler of an entire universe devoted to bad TV. The Joker might have tried to take over the airwaves at various points in his career, but Mojo makes him look like a joke by enslaving a whole universe of "Spineless Ones" to be the audience for his (admittedly pretty entertaining) shows. And wouldn't you know it, most of these twisted programs involve baby versions of the X-Men and other heroes.
Mojo has an unhealthy obsession with creating X-Babies in particular, and though he has attempted this scheme several times, the kiddos always turn on him every single time. He's turned the existing mutants into infants, created fresh baby versions separate from the X-Men that inspired them and even went as far to babify the entire Age of Apocalypse. Oh, and also the Avengers at one point. If you find a murder clown scarier than a vile, living garbage dump, extra-dimensional network exec with an obsessive need to create fighting babies, you might be the sociopath.
Arcade doesn't have any special powers; all he's got is an iconic look, a crazed grin, and a passion for creating theme parks... named "Murderworld." Arcade takes your sickest, most depraved moments from your days playing roller Coaster Tycoon and makes them a reality. He's like the Walt Disney of Assassination. Though he has struggled with finding a prime nemesis, Arcade remains one of the most enduring villains in the Marvel canon. It helps that he's a total dick.
Goofballs like the Joker might be content with jack-in-the-boxes with guns, or chattering teeth that'll blow your face off, but Arcade has made like 20 different Murderworlds that are all about death-hidden-behind-some-whimsy. Dude's got range, too. The countless Marvel regulars that've run Arcade's murder gamut include Spider-Man, Ghost Rider, Doctor Doom, The Thing, the Micronauts, and like, ALL of the X-Men.
All the while, Arcade has maintained a wild-eyed grin, always dreaming up his next attraction. His latest scheme involved trapping a whole bunch of teen heroes in a Murderworld compound and forcing them to kill each other, Hunger Games/Battle Royale-style. He even went so far as to kill one of the youths himself, just to set an example.
Lately he's been seen with a more illustrous hairdo, because the only thing creepier than a cartoony killer is one who looks like a rich, eccentric stoner. Just don't call him a clown.
Of all the most off-putting super-powers, mind-control is definitely one of the more unpleasant. The Purple Man took his villain name over his already terrifying given name, Zebediah Killgrave. Though he sounds like combination Amish cult leader and metal band mascot, Kilgrave is actually gifted with the power of hypno-pheromones. Meaning the Purple Man can make you do anything he wants you to do if you get close enough, up to and including eating the dry old ketchup around the top of the bottle.
The side effect of these powers is gaining a purple skin pigment. To be fair to Zeb, he totally rocks it, with a purple wardrobe that makes the Joker (and Prince) look like an amateur. All of his purple-obsessed accoutrement aside, Killgrave is also incredibly deranged. For a long time he was just a C-level Daredevil villain, but in the series Alias, which introduced Jessica Jones (the TV show is due soon on Netflix), the Purple Man really creeped it up a notch.
Near the end of the series, it is revealed that Killgrave held Jones in his thrall for months, seemingly as a sex slave. Then he sent her out to kill Daredevil, but she attacked the Scarlet Witch instead, and the Avengers beat her into a coma. Later on, Killgrave came back and took a stroll with Jessica, making random bystanders poke each others' eyes out and such. But hey, the Joker made those fish smile that one time. That's pretty weird, I guess.