Avatar: The Last Airbender/Nightmare Fuel

• When Aang accidentally burns Katara. She runs off crying, obviously frightened and in pain. Sokka angrily approaches Aang and pushes him to the ground, yelling at him for burning his sister.
• It may be a "kid's show", but there is no way in hell that the bit where Long Feng introduces the replacement Joo Dee wasn't designed to terrify everyone watching, no matter the age. And then, to make matters worse, we later see a room full of women being Brainwashed into being "Joo Dee".
  • The Joo Dees in general. What makes it even more disturbing is the fact that they're a bunch of young women who've been brainwashed into obeying the Dai Li's every command. As far as we know, the Dai Li are all male. You do the math.
  • The music that first plays when Joo Dee is introduced. Just THAT should show you that she's bad news...
  • Even before you know about the brainwashing, that constant, creepy, fake grin the Joo Dees have is very... unsettling.
  • Jet's brainwashing at the hands of the Dai Li.

"There is no war in Ba Sing Se."

• Koh the Face Stealer. An Eldritch Abomination with a centipede body and a silken-smooth evil voice. He has many faces he can wear. Sometimes when he's talking to you, he'll stretch a strange eyelid-like skin flap over his face, and when he removes it, he'll be wearing another face. And when you meet him, you must maintain a perfect poker face. If you show any emotion in your expression at all, he'll add your face to his collection and leave you as a blank.

"You've come to me...with a new face."

• • The whole atmosphere around Koh's cave is carefully calculated to build tension, rising to a peak when Aang sees a monkey outside the cave... a monkey with no face.
  • It's not helped at all by the fact that Koh says something like it's been a while since he's gotten a child's face. That's right, Koh was excited about taking faces from children.
• Fire Lord Ozai.
  • Especially in the scene where we see him (or rather, hear him) burning his son Zuko's face off. Zuko is thirteen years old, crying, and begging for mercy.
    • Zuko's scream. Oh my god, his SCREAM. The poor kid is terrified, and you can practically hear how betrayed he feels.
    • With his own sister cheering on their father. When you watch it the first time, you don't realize who Azula is yet, but when you rewatch it... you realize just how much of a psychopath she is, even if she manages to hide it under a civilized veneer for so long.
    • The fact that he's voiced by Mark Hamill (AKA The Joker) doesn't help.
  • The fact that he's constantly in the shadows and we never really see what he looks like in the whole first two seasons may make him even creepier.
• The nightmare Aang has in "Nightmares and Daydreams". ... just that.
  • My god... that gave me nightmares. A perfect example of Surreal Horror.
  • Toph with no eyes.
• Bloodbending--the art of turning someone into a People Puppet by Waterbending his or her body fluids.
  • When Katara discovers she bent Hama's blood.
• Hama herself. She seems like a kindly old woman at first, but by the time you reach her final moonlight duel with Katara, the animation and lighting make her incredibly disturbing. Wrinkled, twisted features, long willowy hair and skeletal hands with nails like claws.
• The atmosphere of "The Swamp" was incredibly creepy.
  • Early in the episode, the Gaang hears a bird with a cry that sounds exactly like a human scream.
  • The visions. Katara thinks she sees her mother, only for it to be an illusion. She collapses to the ground in tears. Then, Sokka sees Yue, who says in a creepy, echoing voice: "You didn't protect me." She disappears... and when Sokka turns around again, she's right behind him, staring at him blankly, accompanied by a scare chord.
  • The swamp actually has a mind of its own.
  • Huu's swamp-monster disguise made out of vines.
• Never make Wan Shi Tong angry. EVER.
• For that matter, never piss off Katara. For the lovey-dovey mother figure, she is easily the scariest and most terrifying individual of the group. She openly threatened Zuko with death should she find any reason to not trust him, and was a literal inch away from killing Yon Rha in her blind rage. Do. Not. Piss. This. Woman. Off.
• Azula's Villainous Breakdown. Straining at handcuffs, and the NOISES she was making.
  • The entire scene where she hallucinates seeing her mother in a mirror and talking to her.
  • Not to mention the tortured cello that plays during her Villainous Breakdown, right before she slices her bangs off.
• "I am about to celebrate becoming an ONLY CHILD!" If it wasn't clear before how much of a sociopath Azula is, the utter and terrifying glee with which she says that should be the perfect indicator.
• Katara's mother is killed by a Firebender. That means she walked in on her mother's charred body as a little kid.
• The Book Two finale. Aang goes into the Avatar State and rises into the air, encased in a pillar of light. Katara looks on with admiration and awe, the music gets upbeat and seriously epic, and it looks like we're about to see a repeat of the Book One finale...and then Azula fries him with a bolt of lightning, in the middle of the transformation sequence.
• The Avatar State. Aang loses control and turns from a kind, cheerful kid into a cold, merciless Creepy Child with the Voice of the Legion.

"WHERE'S APPA?! TELL ME WHERE HE IS!"

• • In the first episode of Book 2, an Earth Kingdom general attempts to get Aang to use the Avatar State at will. He tries to provoke Aang into entering the Avatar State by actually Earthbending Katara INTO THE GROUND as if she's in quicksand, and she disappears while screaming in pain and fright. Needless to say, this provoked Aang to go into the Avatar State, and he goes berserk and starts attacking everybody in a blind rage.
• The scene in "Appa's Lost Days" of the circus. That episode won an Annie award for its REALISTIC portrayal of animal abuse in the circus. Sweet dreams...