Throughout its run, The X-Files lured in viewers with conspiracy theories and scary monsters. Every week, FBI agents Dana Scully and Fox Mulder pursued their mysterious targets with a combination of science, open-mindedness, and perfect timing. While some fans dig deep into the underlying story that evolves over the course of the show, others prefer the stand-alone monster-of-the-week episodes that delve into the paranormal with humor, horror, and foreboding.
While some of the supernatural villains on this list were stopped in their evil pursuits, others were not so easy to sabotage, making them the most memorable scary monsters on The X-Files. Which of the creatures below kept you up at night when you first encountered them? Who would you be the most frightened to meet in a dark alley? Is the scariest monster from The X-Files still out there?
Episodes: "Squeeze" (Season 1, episode 3); "Tooms" (Season 1, episode 21)
M.O.: Tooms is a humanoid, hibernating creature with a peculiar skeletal system, and he hunts his targets by flattening his body and crawling through air vents. All of his targets have something in common: Their livers are missing. It becomes apparent that Tooms must feast on these organs in order to survive, and his trail of misdeeds dates back to 1903.
How It Ended: When Mulder and Scully first capture Tooms, he is sent to a sanatorium. However, due to the unconventional methods used by Mulder and Scully, Tooms is released and placed into the care of an elderly family. Tooms returns to his liver-eating ways, and the detectives track him to his former apartment, where the bile-covered mutant has made himself cozy with a newspaper nest in an old elevator shaft. Mulder moves quickly, activating the elevator and crushing Tooms.
Episode: "The Host" (Season 2, episode 2)
M.O.: After a radioactive flukeworm infects a Russian freight worker whose boat is docked outside New Jersey, the man is transformed into a worm-human hybrid with a taste for human flesh. Flukeman travels through the sewage system, attacking people while spreading mutant worms from person to person. The creature's goal is reproduction, and Flukeman won't stop until the sewers are full of its writhing, pale brethren.
How It Ended: Mulder slices Flukeman's body in half using a sewer grate at a processing plant, and the case is closed. The episode ends, however, by zooming in on Flukeman's top half as it opens its eyes.
Episode: "Home" (Season 4, episode 2)
M.O.: After the Peacock parents get in a car wreck, taking the life of Mr. Peacock and leaving Mrs. Peacock an amputee, Mrs. Peacock decides to have intimate relations with her three sons in order to keep the family line going. When Mrs. Peacock gives birth to a deformed baby, her sons bury it alive. This off-the-grid, rural brood will do whatever it takes to preserve the Peacock name, and they don't appreciate the FBI and local police interfering with their business.
How It Ended: Through lab tests, Mulder and Scully are able to trace the baby to the Peacocks. With the help of local police, they travel to the Peacock home, where the sons retaliate. A battle ensues, leaving two of the brothers deceased. The oldest brother flees with Mrs. Peacock in a car, implying the pair will continue to inbreed.
Episode: Humbug (Season 2, episode 20)
M.O.: In a Florida community occupied by former circus sideshow freaks, Leonard is an underdeveloped conjoined twin attached to the side of his heavy-drinking brother Lanny. Desperate to find a new person to attach himself to because Lanny is on the verge of liver failure, Leonard detaches himself from his brother by night and cruises the town in search of a new "twin."
How It Ended: The detectives chase Leonard into a funhouse, but the fetal man escapes. As it goes in the circus sideshow world, Leonard becomes dinner for another performer, the Conundrum, known to eat anything. Apparently, Leonard doesn't settle too well, and the episode ends with the Conundrum suffering from a pretty awful stomach ache.