The X-Files/Nightmare Fuel

""Why are you crying?" "Because...you can't kill me.""
 * The subliminal messages people start seeing all over the place in Blood. "KILL 'EM ALL." Oh God.....
 * "I can tell you don't have no children. Maybe one day you'll learn... the pride... the love... when you know your boy will do ANYTHING for his mother." AUGH.
 * The opening birth sequence, with the scream and shot of the umbilical cord being cut, is unforgettable, though Wikipedia makes it sound worse than it is.
 * The scene with the couple getting beaten to death and the accompanying music... *shudder* The cheery song Wonderful, Wonderful has become linked with creepiness in the minds of fans.
 * The episode has the distinction of being the only one in the show's history to be banned from network TV. Honestly, it's surprising it ever made it to air in the first place, but it was something like five years before it was shown again. (As part of a Halloween scare-fest, of course.)
 * Badlaa. Quite apart from the general Squick factor of it all, there's the idea that he can make himself invisible... that scene where the kid is running down the street and he can't see what's chasing him, but can only hear the 'squeeeak, squeeeak, squeeeak...' of the wheels behind him... *shudder*
 * The cursed doll from Chinga. Particularly the way it speaks when attempting to kill the mother. "Don't play with matches. Let's play with the hammer."
 * "I want to play!"
 * The horrible vision of the charred, bloody doll in Clyde Bruckman's Final Repose.
 * The Calusari. "Be careful. It knows you now."
 * Two simple red, glowing lights become a symbol of fear after Detour. To make it worse, the beginning scene that shows the glowing red eyes coming from the ground is used as the main menu on the DVD for the episode.
 * The last shot of the episode -- the eyes opening up under Scully's hotel bed -- was incredibly creepy.
 * The pit with the bodies.
 * Keeping Donnie Pfaster's demon form in quick, darkened glimpses in Irresistible was how you do it right. Or very very wrong.
 * As if the first time wasn't bad enough -- they brought the bastard back for a sequel episode!

""It's here.""
 * Donnie Pfaster himself. They Look Just Like Everyone Else indeed.
 * Invocation, especially when Scully plays the tape backwards. -shudder-
 * The alien bugs of Darkness Falls attack you in the dark, rather like the Vashta Nerada of Doctor Who. Turn the light off, now, and sleep tight!
 * Or how about someone emerging out of a small cut in Scully's hand fingers first in Fresh Bones?
 * Eugene Victor Tooms, possibly the most popular (and most terrifying) monster to appear on the series. Trust me, once you see him in action, you'll never go near another air vent again.
 * Oh, so seconded. Recall his introduction in Squeeze: after an establishing shot of a busy city street at rush hour, the camera settles on a sewer grating and slowly, slowly zooms in on it. Pretty soon, we begin to see a pair of cold, yellow eyes staring predatorily out. Skip all the way to the end of the episode: Tooms has been put in prison, but notices that there's a hole in his cell door through which he can escape. He begins to smile in a way that's indescribably innocent yet perverted at the exact same time, and this HIDEOUS sound effect plays over and over again as the screen fades to black. It was only the third episode of the series (and the first standalone), but it set the tone for the entire show. One of the scariest episodes ever.
 * Folie à Deux. Your boss is a horrible insectoid creature who vibrates like he's out of sync with reality and can move faster than you can blink. Worse, he's systematically turning your coworkers into the living dead, and everyone thinks you're delusional because you're the only one who can see it.


 * "We're not who we are" (Ice), although admittedly possibly coloured because it's basically The Thing but science-y.
 * Teliko, gives us a man who steals the pigment from his victims. Just the opening death scene gives me chills.
 * Leonard Betts, and the storage locker sequence.
 * One episode has a subplot where Mulder and Scully discover a hidden camera and stacks of video tapes behind a family's bathroom mirror. Earlier, you see the eyes of the a man watching the woman undress as he breathes heavily. She has two boys. And in confession, he says he loves those boys.
 * The Host, in which a giant mutant flukeworm that looks part human goes on a sewer rampage biting people. However, the most horrifying moment of the episode was not the flukeman himself, but the scene in which a bitten worker THROWS UP A FLUKEWORM IN THE SHOWER. AHHHHHHHHH!!!!!
 * Die Hand Die Verletzt. The devil loose in a small town controlled by the satanic PTA! God... that pig fetus dissection...
 * The Black Oil hits a whole bunch of Primal Fears right on the nose, especially bodily invasion-related fears (it slithers under your skin and into your eyes).
 * Field Trip. Particularly freaky were the scenes where in the form of gooey yellow acid, and especially when a whole room, including the people in it, dissolves into the acid. The whole concept of the episode is both High Octane Nightmare Fuel and Paranoia Fuel.
 * Seconded. Mulder and Scully were experiencing, together, what very much seemed like reality, but in fact they were trapped under ground. Makes one wonder where the All Just a Dream ended. Maybe Mulder and Scully actually died underground, and the rest of the series was just a hallucination.
 * Soft Light. The clear despair and self-loathing Tony Shalhoub's character feels for what he is inadvertently doing, and the genuine fear and horror as he tries to warn people away from his shadow is bad enough... but what the shadow itself does... *shivers and curls up in a ball, rocking back and forth*
 * Pusher gives you an evil bastard who can control you with his mind, forcing you to shoot yourself or set yourself on fire, or even induce a heart attack using nothing but words over a telephone.
 * The beginning of the episode Beyond the Sea has Scully's parents over at her place for a dinner. After they've left, she wakes up on the couch later at night and sees her father sitting on the armchair. She says she thought they had gone home already, but he doesn't even react. The phone rings, she turns away, looks back and her father has disappeared. She answers the phone and her mother tells her his father died of a heart attack an hour ago. Just the way he's sitting there, with a glassy stare, lips moving but no words coming out--
 * Brad Dourif as Chucky from Childs Play has a creepy laugh. Brad Dourif walking slowly past Scully softly singing 'Somewhere... Beyond the Sea...' on the other hand...
 * The scene where the plastic surgeon in Sanguinarium is removing his own face.
 * THE WHOLE EPISODE!!!!!! Squick and Nausea Fuel abound. Vomiting needles. Bathtub full of blood. A guy getting his organs ripped out by a liposuction device. Gruesome plastic surgery accidents. Don't ever watch that episode, EVER. It makes "Home" look extremely tame.
 * The theme music is creepy by itself, and the opening sequence is full of disturbing images: the human silhouette falling onto the image of the hand with the one red finger segment. Just the juxtaposition of the two pictures suggests a story -- reading that the hand image is an example of Kirlian photography is unsatisfying by comparison.
 * How about the individual taglines for some episodes? Some of them are creepy on their own. RESIST OR SERVE, anyone? TRUST NO ONE
 * Hellbound, which is about people being skinned alive.
 * Badlaa. Orifice Invasion at its most squicky, and the sound of squeaky wheels should not be that terrifying.
 * Small Potatoes. Monster of the Week (A man who is a shapeshifter) inpersonates Mulder for the few days, while the real Mulder is trapped in a hospital cellar. Mulder manages to get out, but the fact that everyone around actually took the fake Mulder for real can induce heavy amounts of Paranoia Fuel.