Will-o'-wisp

Will-o'-wisps were malicious creatures that appeared as torches or lanterns seen floating through swamps.

Description
The will-o'-wisp appeared to be nothing more than a hazy ball of light, colored white, blue, green, or yellow, growing as brightly as a flaming torch. As such, it was easy to mistake one for a lantern or torch, especially in the foggy marshes they dwelled in. In fact, its faintly glowing body was just a transparent ball of spongy matter around 1 foot (30 centimeters) wide and weighing around 3 pounds (1.4 kilograms). Although they had no vocal organs, will-o'-wisps could vibrate to emit a ghostly sound, with which they could speak.

Abilities
A will-o'-wisp could extinguish its glow, becoming for all intents and purposes invisible. They typically did this when surprised or frightened.

Will-o'-wisps had total spell resistance, making them to most spells, apart from magic missile and maze.

A will-o'-wisp could discharge electricity, inflicting small electric shocks on attackers.

Personality
They were wicked entities that consumed the potent emotions induced by horror, panic, and death. Posing as lanterns, they reveled in luring travelers away from safe paths, bewildering them, and finally leading them into deadly danger in the swamps, where they could then feast on their desperate emotions.

Combat
A will-o'-wisp would avoid combat if at all possible, but would attack with electric shocks if pressed.