Nightmare Fuel / A Wrinkle in Time

The original book

  • The Black Thing - the grandaddy Eldritch Abomination.
  • IT, a giant disgusting brain that enslaves your circadian rhythms if you get too close to IT. IT is the Hive Mind for the entire planet of Camazotz, subsuming select minds within ITself and cowing the rest into fearful, blind obedience.
    • And it's rammed home exactly what the kids are dealing with when Charles lets slip how IT thinks of itself:
      Charles: IT sometimes calls ITself the Happiest Sadist.
    • An actual nightmare: all roads lead to IT.
  • At one point, the kids are accidentally transported to a two-dimensional planet for a few seconds. It nearly kills them.
  • ITs servant, The Man With Red Eyes, who talks about the potential enslavement of the universe in the politest terms possible and doesn't open his mouth when he talks. He actually laughs at one point, a literal case of Hell Is That Noise. Then he takes control of Charles Wallace...
  • The fate of the boy with the ball, who is seen being tortured for bouncing his ball out of sync with the other children.
  • The rather casual, banal way which Charles (under control of IT) explains how Camazotz deals with illness - even minor ailments such as the common cold.
    Charles: We let no-one suffer. It is so much kinder to simply annihilate anyone who is ill. Nobody has weeks and weeks of runny noses and sore throats. Rather then endure such discomfort, they are simply put to sleep.
    Calvin: You mean they're [literally] put to sleep while they have a cold, or that they're murdered?
  • Tessering: what does nothingness actually feel like?

The 2018 movie
  • The trailer gives us our first look at the city controlled by IT (possibly Camazots). The place may look colorful and innocent. ...But it's not. On closer inspection, you notice the children are bouncing their toy balls in the most uncanny synchronization. Everybody in that village talks in sync. With the exception of the village being colorless, this follows the book all too closely...
    • Even scarier? The way the mothers look right at the screen and ask "Are you lost?" It's as though IT detects that there's something or someone (the audience) intruding on ITs 'body', and in the most thinly veiled threat, understands it must be somehow removed...
  • The downright chilling delivery of the trailer's final line:
    "The only thing faster than light... is the darkness."

http://tvtropes.org/pmwiki/pmwiki.php/NightmareFuel/AWrinkleInTime