This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Oblivion Island: Haruka and the Magic Mirror
The Baron's mechanical disguise is pretty scary, especially with his stretchy arms. Compared to everyone else he seems mechanical and very doll-like.
when Haruka is first entering the thieves hideout, she and Teo talk about what they are going to do when the tunnel gets slightly dark, and three toys suddenly appear, then more toys silently fall into the cart, then even more, before they straight up try to swarm Haru.
Haruka falling straight into the 'lava', even though it turns out to be harmless paint/syrup.
The giant plush robot.
Oblivion Drops can cause memory loss, and the Baron intends to use one to make Haruka serve him. They hold her down and attempt to force her to eat one via a creepy pair of rubber lips.
Cotton being ripped in half by an enraged baron just to spite Haruka. It's also kind of disturbing how easily he flips back to acting nonchalant afterwards.