slender... im not sure if you're talking about widepixels or not. lower-res stuff is more terrifying i would say than higher-res because it doesnt look like what we expect to see. I also find vector art terrifying because it creates this sense of impending doom, as though it will destroy us. but that might just be me. DARKEST DUNGEON for instance, the art for that is top notch. but the interface isnt great. if they can work out their interface stuff we'll be extinct. you need to build up lore to do properly scary stuff. kriss straub and candle cove - he's good at that.
again, make a study of borges, lovecraft, and the influences of lovecraft, and who he influenced.
there's a lot you can borrow from the movies, pixel art objects as 'found objects', examples of outsider art. glitch stuff in general. guys like DAVID OREILLEY, who did a pretty messed up episode of adventure time, the lowpoly glitch episode, 'a glitch is just a glitch', but also for his personal work, 'the external world' and 'please say something'.
adventure time does creepy well because they can hide it in something cute.
do things that make people uncomfortable. the discussion on here of the uncanny valley, in another thread, should serve.
secrets, and the threat of secrets.