Horror is a remarkably difficult emotion to bring about organically. Games and improvised narratives especially tend towards the easier to promote terror when attempting to develop fright.

What follows is a tool you can use to create horrific images on the fly.

Take some form of oracle system that randomly produces images and ideas. You may have a set of such dice lying around, you might use Tarot cards… Choose one aspect of that image / idea. For example, a lightbulb could offer its luminescence, its filament, its transparency. Select a part of something else to be used in the narrative. For example, glance at the nearest person; settle on the first limb / feature you spot. Grant the feature from the random oracle to the aspect of the desired element. For example, the nails on someone’s hand might be glassy and transparent; their breath gives off a faint glow in the shadow of the glade.

If you’d rather this as a motto:

Assign, refine, combine.

Some examples, applied to a newly discovered corpse: