This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / LSD: Dream Emulator
The Grey Man. Damn. It's some kind of shadowy, featureless creature that takes the general shape of a man and appears in front of you or behind you, and slowly and silently glides towards you. Usually the screen flashes and he disappears... only to continue following you a few seconds later, silently, without you noticing. Touching it immediately kills you and prevents you from reliving the dream, in addition to erasing texture progress- the only way to really die in the game. It doesn't really help that it mostly appears in Happy Town, a place filled with toys and bright colors. What the heck is this unspeakable atrocity doing in a children's playground?!
Other than the Grey Man, It's safe to say that 99.9999% of this game is the very incarnate of this Trope just because it's all so weird.
Most characters lack any kind of facial features. It doesn't matter if it's due to technical restraints, it's unsettling. The ones that do have facial features... look odd.
The Flesh Tunnels and the demonic babies spinning around inside it.
Violence City, aka Violence District. Just...that place. There are severed limbs in the trash cans, streets filled with dead people with blood around their necks, women hanging from streetlamps who fall on you, several crazy residents, including one who shoots you (with an absurdly slow bullet), creepy letters or words written in blood, and most of the ways to die in the game.
One link puts you at the top of a very high building with no visible ground and forces you to jump off to your death.
The women whose heads fall off when approached-said heads having no faces- and glide towards you while your controls are suspended.
Walking under streetlamps in this area can sometimes cause hanging women to instantly materialize right in front of you with a Scare Chord, and also temporarily freeze your controls.
The pterodactyl figurine in the Cottage. Without warning, it dives into your face and links you once you enter the room.
The black wolf that basically slits your throat once you encounter it.
What about the Abyss Demon? A huge Satan-looking demon who pops up from the edges of the cliffs in the Overworld.
And what about the huge freaking sun with a face on the prism-y bridge? There is one on each end of the bridge, so if you walk forward, see one, and turn back, there's also another one behind you. The texture of the sun also changes sometimes, so you can't expect the same look each visit.
The Giant Baby, who sometimes appears in the room directly to the right of the one you start out it, and throws his head at you.
The Nodding Men, who are sometimes in the ponds in Kyoto.
Certain textures that have eyes or faces on them.
The "downer" texture specifically. Basically gives everything a red warped look, the appearance of the settings are heavily distorted, and uncanny beady eyes appear on many elements that either never had eyes to begin with or had eyes that were otherwise less... unsettling. The other three "main" textures at least have some consistent theme to them ("normal" texture, kanji writing everywhere, images of women everywhere), this set just seems to specifically make everything scarier and make even less sense than the dreams already do.
Sometimes a sick woman will appear in the hotel area, lying on a bed. In a downer dream, she's already been dead for some time, which is represented by a freakishly detailed "rotting skull" texture over her face.
The Kanji Faces, who appear mainly in Kyoto to spit kanji at you and fly away.
The Spectres, who appear at the base of the hotel where you start out.
The Teddy Bear in the hotel, who tries to hug you and follows you as long as you remain there. And who's standing watching a blood-splattered TV that kinda looks like Uboa of Yume Nikki.