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Tiny undead, chaotic evil
Damage Resistances acid, cold, fire, necrotic, thunder; bludgeoning, piercing, and slashing from nonmagical attacks
Consume Life. As a bonus action, the will-o'-wisp can target one creature it can see within 5 feet of it that has 0 hit points and is still alive. The target must succeed on a DC 10 Constitution saving throw against this magic or die. If the target dies, the will-o'-wisp regains 10 (3d6) hit points.
Ephemeral. The will-o'-wisp can't wear or carry anything.
Incorporeal Movement. The will-o'-wisp can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.
Variable Illumination. The will-o'-wisp sheds bright light in a 5- to 20-foot radius and dim light for an additional number of feet equal to the chosen radius. The will-o'-wisp can alter the radius as a bonus action.
Shock. Melee Spell Attack: +4 to hit, reach 5 ft., one creature. Hit: 9 (2d8) lightning damage.
Will-o'-wisps are malevolent, wispy balls of light that haunt lonely places and battlefields, bound by dark fate or dark magic to feed on fear and despair.
Hope and Doom. Will-o'-wisps look like bobbing lantern lights in the distance, although they can choose to alter their colors, or wink out completely. When they activate their lights, will-o'-wisps offer hope, hinting of safety to creatures that follow them.
Consumed by Despair. Will-o'-wisps are the souls of evil beings that perished in anguish or misery as they wandered forsaken lands permeated with powerful magic. They thrive in swampy bogs and bone-strewn battlefields where the oppressive weight of sorrow stoops even heavier than the low-hanging mist and fog. Trapped in these desolate places of lost hope and memory, will-o'-wisps lure other creatures toward dismal fates and feed on their misery.
Agents of Evil. Will-o'-wisps rarely speak, but when they do, their voices sound like faint or distant whispers. In the miserable domains they haunt, will-o'-wisps sometimes form symbiotic relationships with their wicked neighbors. Hags, oni, black dragons, and evil cultists work with will-o'-wisps to draw creatures into ambush. As their evil allies surround and slaughter creatures, the wisps hover above them, drinking the agony of a last breath and savoring the sensation as the light of life goes out in a creature's eyes.
Undead Nature. A will-o'-wisp doesn't require air, drink, or sleep.