Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Nightmare Fuel: Raven
The scene on the first day of the final week of The Dragon's Eye, in which the remaining contestants, after stepping through the portal to start the final stage of their "quest" in the land of Darkness, were faced with a bunch of screaming Feral Children, who are roaming around the place. These children are said to be people who previously tried to claim the Dragon's Eye but failed. This was more unsettling than scary. But then you realise that the feral children are being played by the previously eliminated contestants who we watched vanishing altogether when they "died". Whether they are intended to be them for real is unclear, but it certainly implied, and the sight of them jeering and laughing at their former teammates, then trying to hold them captive while beating on the doors, still jeering... I'm half surprised there are younger kids still applying to be on this show.
There's Raven's reaction to it. He's madder than we've ever seen him, threatening Ervan in a way almost devoid of his usual Badass Boast, and openly ranting at and admonishing these feral kids who are so scared of him that they let the contestants out right away. To think that they might have been his former students...
Ash cloud in the Blasted Mountain challenge was creepy. It was wheezing, as if the cloud itself was alive!