Ohhhh!!!! There's tons of tropes I'm nuts for! I'm gonna list them all out cause I have a solid handful:
- Duel personas, or the self breaking apart into doppelgangers. Extra points if it plays into the horrors of being perceived.
- Wonderland-esque settings. Alice in Wonderland is one my favorite works of fiction ever, so I love any stories that take a young protagonist and thrust them into a strange fantasyland (think OTGW, Pan's Labyrinth, or Coraline).
- Eldritch locations (I think I just like places that are weird and nonsensical lol). I love the thought of a location being actively hostile or built around tormenting whoever inhabits it. The best examples would probably be the house from House of Leaves of Silent Hill.
- Dreams or mental worlds as a thematic or plot device in any capacity.
- Characters who are timid and reserved, but either have a dry, sarcastic side or have an underlying darkness to them.
- Guilt, trauma or grief being represented by an ominous being that plagues the protagonist (think Pyramid Head or Something from Omori).
- Themes of existentialism, or escapism vs reality.
- Stories in which several faucets of society and isolated behaviors interweave into something horrible, like Twin Peaks or Paranoia Agent.
- The general message of "life can be hard, lonely, and painful, but living it and connecting with others will always be worth it".