- Piella from "A Matter of Loaf and Death" is a surprisingly terrifying villain, due in part to being a serial killer.
- Her death involves being eaten by crocodiles. We don't see it, but we hear it.
- Her abuse of Fluffles is disturbingly similar to that of someone abusing their child.
- The part near the beginning of "A Close Shave" when Wallace panics about Shaun going through the machine can be pretty alarming & disturbing to kids, especially because of the tense background music. Leads to Mood Whiplash when all it does is shave him bald.
- The revelation that Preston is a robot, especially when he rips himself out of the machine. But that's nothing compared to him attempting to turn Wendolene and the sheep into DOG MEAT!
- Hell, practically every scene Preston is in is rather terrifying. His unnerving gaze really sells it.
- The 525 Crackervac (pictured above) from the Cracking Contraptions short of the same name is kinda freaky in appearance with its red eyes and snapping metal teeth.
- "The Right Trousers", a live-action parody from The Lenny Henry Christmas Show back in 1995, is full of this, most notably with Wallace and Gromit's faces.
- Feathers McGraw from "The Wrong Trousers" is this in spades. Despite looking exactly like a normal penguin, there's this unearthly sense of soullessness in his eyes. His every move is careful, calculated, and utterly ruthless, willing to commit any number of crimes or misdeeds to attain what he wants. It's legitimately unnerving to see him move onscreen, as there are no anthropomorphized movements or qualities to him - he is just a penguin that wants to hurt people.
Nightmare Fuel / Wallace & Gromit