This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Land of Stories
The character of Mrs. Peters. She is an Ice Queen with little care for anyone but Alex, and is even willing to call one of her students an idiot. Sadist Teacher indeed. She seems to warm up a bit in later books though.
Bree nearly crashes a plane in the German countryside in An Author's Odyssey. It is revealed shortly afterward that the autopilot was on, but if they'd crashed...
The fate of the 24 missing children from Beyond The Kingdoms. Crosses over a lot into Adult Fear.
Dead Man's Creek has a habit of changing the direction of its flow, which is tame enough, but it sends coffins with bodies inside downstream every time it does. The cause of this is revealed to be Morina, who needs a convenient way to get rid of her victims after she drains all of their youth to make potions.