The will-o'-the-wisp, or wisp, is a nocturnal creature of Xanth.
Wisps are described as a light of sorts. It commonly tries to capture the attention of unsuspecting passer-bys. With mischief it lures it's prey out into the wilderness, then the wisp would turn off it's light, causing the victim to become lost. Many victims were never seen again, becoming prey to whatever hostile magic they might stumble across while trying to find their way home.
Due to it's light, those lucky enough to survive are often unable to provide an accurate descriptions of it's appearance.
- A Spell for Chameleon, Chapter 1