Will-o-Wisp
A Will-o-Wisp (known by many, many variations of that name, such as Will o' the Wisp) is a strange monster that takes the form of a glowing orb of light that tends to appear in dark forests or near swampy regions. Whilst sometimes portrayed as merely mischievous, more often, the will-o-wisp is a malign trickster who uses curiosity (and perhaps a dab of mind-control magic) to lure victims into following it, invariably delivering them to danger in the form of a natural hazard or a monster.
Depending on the setting, will-o-wisps may be portrayed as a kind of ghost, an elemental, a fairy, or some sort of aberration.