This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Nutcracker Prince
It comes in the unexpected twist where a dying mouse king suddenly appears one last time to try and kill Clara, though if it's just to spite the Nutcracker or if he's losing his senses and can't tell she's not the Nutcracker is anyone's guess.
Keep in mind that he was able to come all this way and attack her after being stabbed in the heart.
One other thing to note when the Mouse Queen comes to Princess Perlipat's bedchamber, as she chants her spell, her voice starts merging with a very creepy like voice and as that happened, her claws in the shadows looked very disturbing around the sleeping girl.
The Mouse Queen's death can be a bit disturbing, especially since we can see her corpse flattened underneath a large pillar when the pillar fell on top of her.