Ildriss were either completely invisible, or they resembled a cloud-like mass with vaporous tentacles and red gleaming eyes. The color of their cloud form varied slightly. When traveling, ildriss were always invisible.
Ildriss were able to get the initial jump on any creature. When attacking, they transformed into their cloud form, striking out with their tentacles that were hardened by small bits of material.
These creatures could only be harmed by magical weapons. Additionally, all air and lightning-based magic was useless against them. Spells of this nature were dispelled when an ildriss came within 50 feet (15 m) of them, including spells with permanent effects. Magical items were immune to this dispelling effect.
Much like their windy nature, ildriss made and broke relationships with ease. They belonged to dynamic cliques on the Elemental Plane of Air, but were always solitary creatures when encountered on the Prime Material Plane.
Groups of ildriss did not have an established hierarchy, instead ildriss followed the lead of others with defined goals so long as those goals suited them as well. Ildriss served as spies for Yan-C-Bin, the Elemental Prince of Evil.
Other races of the Elemental Plane of Air viewed ildriss with disdain, considering them to be parasites. Ildriss often spied on other creatures for days before attacking or taking action.
Ildriss fed on clouds, air, breezes, birds, and small elemental creatures. During the mating season they maintained strict territories, becoming instinctively aggressive to any intruders. These territories were pockets of air that moved about and not simply the air located over a stationary object or piece of land.
Rumors abounded of good-hearted ildriss who abandoned the service of Yan-C-Bin. These timid creatures were known as fog ildriss.