This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Shadows Of The Azure
The Shadow labriynth of Ragna, taking the form of a graveyard.
Shadow Ragna taking the form of a ghost when Ragna first sees him.
Nyarlathotep's torture of Taokaka, along with making her smarter through the fruit of knowledge, is cruel, cold, and completely sociopathic, and Nyarly loves every minute of it.
Bang's Shadow Labyrinth, which is a militaristic castle coupled with a serene garden, which only adds to the Mood Whiplash. Or, you could see the garden as a stoic moment, only adding to the creepiness of the rabid militarism. Especially when you realize that this comes from our resident hammy ninja of love and justice.