My "first things that come to mind" list:

Creepy horse, 6 eyes, 3 legs, blood, bones, cobwebs, dirty waters, flies etc

Horse looking at his reflection (water or mirror), his current self is old, ribby and sad and his reflection if his younger self

Horse tangled in snakes, in a forest or something similar

Horses head (and a little neck) just above water with a "in a hurry to get away" expression

Horse partially in / out of water, underwater being sharks or something

Horse emerging from the ground, lots of dirt, tangled hair

Horse emerging from a dark forest, skin walker type, looks like a horse but not really, creepy, eerie vibes, strange eyes (maybe more than two), fangs, antlers or horns

Creepy horse with different body parts from different animals (example: one antler and one horn, lizzard tail, whale fins etc)

Cowboy horse wearing boots, brown vest etc

Horse sitting on a branch, long ass hair with plats (braids)

Horse laying on the beach (or standing), shells on the body, in the hair, flowy hair, soft colours

Huge cobweb and spider horse, freaky lookin :3

I might be back later c':