Mine is a black human-shaped shadow, it has to be pitch black with no details, moving unnaturally.
Kind of like the one in the Bad Apple video (but that one moves naturally so it's not really scary).
Like this painting (The Melancholy and Mystery of A Street), scary as hell:
View attachment 48563
Fairly rational...
But just for you buddy, I'll stop walking around your room at night.
For their defense, i kindaaaaaaa can understand and explain their fear. (i dont have it though. I hope XD)
There is this Halo Tv show (not the recent one but a more niche one)
where a group of soldier go to a "remaining halo ring parts, a part of the ring masterchief bombed". (floating near the sun of a system)
There, there is a alien thingy. Which is basically a colony of worms that of course eat flesh. (horror style trope where the team try to escape the planet, while chased by a scary monster).
>>>>>>>>>>>>>>>>>> And what i want to talk about, is that there is a scene, where on top of the cliff, you, they (the team) see a
shadowy silhouette.
And the smart person stop others, explaining its a trap, not a surviving teammate.
Zoomed-in, its basically the "worm colony" trying to mimic a human shape. To attract them and think its a survivor.
And you see the "shadowy" thing, sometimes do unnatural gestures/movements. (just like OmegaC said).
And yes, it is indeed quite creepy and scary.