Will-o'-wisp

 are a type of spectral undead creature.

Appearance
The will-o'-wisps encountered by the Mighty Nein in Siff Duthar's abandoned research facility had a fading dull yellow-green glow and were surrounded by sparks. The wisps on Rumblecusp rose out of the pools scattered about the landscape in the Shaded Tangle were strange little eerie blue flame lights.

Abilities

 * Damage Resistances: acid, cold, necrotic, thunder, and nonmagical physical weapon damage.
 * Incorporeal Movement: Will-o’-wisps could fly through other creatures and objects.
 * Attack:
 * Shock: Will-o’-wisps could attack targets with surrounding lightning.