Will-o-the-wisps

A head sized or smaller ball of dimly glowing light in shifting colors. They are leech-like spirits which sustain themselves in the mortal realm by draining the energy of other spirits. To achieve this they display themselves nighttime, usually close to roads and waterways, in an attempt to tick travelers that they are distant campfires. Once far from civilization the will-o’-the-wisp will attack its prey by way of horrific images, attempting to paralyze it or drive it mad. If successful the creature will linger by the body and slowly drain its power while the victim will eventually succumb to starvation or thirst.

In the Spirit Realm will-o’-the-wisp behave exactly the same, but they lure other spirits into their tempting dreamlands, only to turn them into nightmares. The origin of will-o´-the-wisps is unknown, but their skill in the illusion magic school suggests they may once have been mages.

Alchemy
If a will-o’-the-wisp is killed in the mortal realm it will leave behind a fine powder known as glow dust. Glow dust glows faintly in the dark and can be used as a good quality alchemical ingredient.