For many of us horror fans, The X-Files was one of the most formative TV shows of our lives. Dense, dark, thought-provoking, and often scary as hell, The X-Files brought a level of fear to television that most of us had never seen back in the days before Buffy the Vampire Slayer, let alone prestige TV projects like True Detective. Originally airing from 1993 to 2002, The X-Files revolved around FBI special agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson), who specialize in investigating unsolved cases that often cross into paranormal territory.
Combining conspiracy theory continuity with freaky “monster of the week” episodes, The X-Files was vividly imaginative and often terrifying—maybe more so than network TV was even really ready for. Here are 13 of the show’s most shocking episodes that we still think about in the dead of night, when we hear a strange sound on the stairs or under our beds…
“Squeeze” Season 1, Episode 3
One of the show’s earliest “monster of the week” episodes also introduced one of its most memorable monsters: Eugene Victor Tooms, a man who can squeeze his body into impossibly tight spaces. It’s a skill that’s allowed him to pull off a string of murders in locked or otherwise inaccessible rooms, and harvest the livers that he needs before he goes into hibernation. (You know, as one does.) Tooms was so popular that he showed up again later in the same season, in an episode that you’ll also find on this list…
“Eve” Season 1, Episode 11
Creepy kids are a horror staple for a reason, and twins can be even eerier—just look at the Grady girls in Stanley Kubrick’s The Shining. The creepy kids in this Season 1 episode of The X-Files, played by Erika and Sabrina Krievins, are more than just your average twins. In fact, they’re the murderous result of a sinister fertility clinic that has been practicing human cloning.
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“The Host” Season 2, Episode 2
Of all the monsters from The X-Files, the freakiest may well be this episode’s creature, the so-called “Flukeman.” Born from the Chernobyl nuclear disaster, this horrific creature not only haunts the sewers of New Jersey, but also infects people with parasitic worms. So even if you aren’t unsettled by the Flukeman’s pale shape and terrible maw, there’s that added fear of infection waiting in the wings…
“X-Cops” Season 7, Episode 12
One of the most unusual episodes of The X-Files, this Season 7 entry was actually a crossover with the early reality TV show Cops, an idea pitched by writer Vince Gilligan several times before the showrunners finally gave him the greenlight. The episode features a police officer who is being followed by a camera crew from the show Cops as he crosses paths with Scully and Mulder. Together, they tangle with a mysterious, seemingly invisible creature that is killing the residents of a Los Angeles neighborhood—but not before assuming the form of their worst fear!
“Detour” Season 5, Episode 4
While on the way to an FBI seminar, Mulder and Scully get sidetracked by creatures in the Appalachian wilderness that can camouflage themselves perfectly, save for glowing red eyes—think Predator, X-Files style. The camouflage scenes were achieved with complicated “bark suits” and early digital effects, and the shoot was hampered by constant rain, but the resulting episode is plenty creepy.
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“Sanguinarium” Season 4, Episode 6
Adapted from a spec script written by two fans of the show, this bloody Season 4 installment just might be the goriest episode of The X-Files ever made. Its villainous, witchcraft-practicing plastic surgeons not only melt their victims with acid, but can also teleport surgical tools into their bodies from a distance or make them vomit up pins. Gruesome stuff for primetime TV.
“Tooms” Season 1, Episode 21
The terrifying return of Eugene Victor Tooms, the series’ first “monster of the week” character, was co-written by Final Destination director James Wong and Glen Morgan, who had created the character together back in “Squeeze.” This episode sees the ultimate demise of Tooms—but not before he engages in some creepy shenanigans, including framing Mulder for a gruesome murder.
“Soft Light” Season 2, Episode 23
Tony Shalhoub plays a particle physicist whose shadow has become a deadly black hole in this eerie, Twilight Zone-esque episode. Chester Banton doesn’t want to harm anyone, but after an accident with a particle accelerator, his shadow destroys anyone it touches. On the run from ominous government forces that want to exploit him, Banton crosses paths with Mulder and Scully, who believe that they’re investigating cases of spontaneous human combustion.
“Chinga” Season 5, Episode 10
When you hear that Stephen King co-wrote an episode of The X-Files with series creator Chris Carter, you can bet it’s going to be a creepy one. King has always been a fan of reworking old horror tropes that have been run ragged, and in this case he takes on one of the dustiest ones around: the cursed doll. It may be a familiar theme, but let’s face it: creepy doll stories just work. In “Chinga,” the eponymous doll forces people to kill themselves in gory fashion. Chinga is no exception to the creepy rule—especially when it reappears as a gigantic version of itself.
Related: 9 Scariest Haunted Dolls You Do Not Want in Your Home
“Die Hand Die Verletzt” Season 2, Episode 14
Any time an episode opens with the revelation that a bunch of faculty members at a local high school are actually Satanists, you know you’re headed into some weird territory. “Die Hand Die Verletzt” has fun with the “Satanic panic” that gripped the nation in the ‘80s, and one of the things that makes this Season 2 episode so chilling is that it actually starts out kind of humorous before taking darker and darker turns that we certainly weren’t expecting.
“Roadrunners” Season 8, Episode 4
This brutal episode follows Scully to a small town in the Utah desert, where a strange parasitic creature that resembles a banana slug has been discovered. The locals believe the creature is actually the Second Coming of Christ, and are willing to stone people to death in order to protect it.
“Folie A Deux” Season 5, Episode 19
Many episodes of The X-Files find Agent Mulder skirting the edges of what is considered consensus reality. His is a life filled with conspiracy theories that turn out to be true. But seldom has his own sanity been as questionable as in this Season 5 episode. What seems like a simple case of one person’s unfortunate delusions takes on a distinctly different— and much more chilling—quality when Mulder begins to share those delusions, and to suspect that there might be more to them…
Related: 9 Haunting Cases from Unsolved Mysteries That Have Since Been Solved
“Home” Season 4, Episode 2
Ask any X-Files fan to name the show’s most disturbing episode, and this Season 4 oddity is bound to top the list. First shown in 1994, “Home” was deemed so brutal and graphic that it was banned from being re-aired during syndication for years. The plot follows Mulder and Scully to the seemingly idyllic town of Home, Pennsylvania. There, they run afoul of the Peacock family, an inbred clan of nearly-feral killers à la the Sawyers from The Texas Chain Saw Massacre.
Featured still from "The X-Files" via 20th Century Fox Television