Local mythology. If you’re in Ceannis, and a couple of figures pop up on your shoulders to start giving moral advice, here’s what they’ll look like.
Imps are traditionally depicted with horse-tails and feathered dragon-wings — very large, to distinguish them from the wings that some normal humans have. No horns, because those are associated with dogs, and loyalty and friendliness and all that good stuff. Wear a lot of blood-red and shadow-black.
Faeries wear crowns of flowers, for the same reason brides and grooms do. Butterfly wings, not feathered ones, to distinguish them from imps (and dragons). They wear a lot of white and pastels.