The Runalongs are rare in worlds without fast transportation. It seems they are brought into being when someone, bored by a journey, looks out to watch the countryside go by. They daydream of a creature that follows their path (guarding? Or hunting?) and suddenly, without fanfare, it appears.

Runalongs have little in the way of ecology, but they are known to eat other dreams. Sometimes if the one who called them is particularly lonely or afraid they will get closer and even speak in humming voices without opening their mouths. But the second you stop moving, the creatures turn and vanish behind themselves, disappearing to wherever fantasies come from.

A Runalong can also have other forms; a humanoid figure (without distinct features) is common, and these may also ride things that are supposed to be horses. If only we were better at imagining, then they might not look so terrifying.