Phiuhl

Believed to be the insubstantial spirits of slain elementals, phiuhls haunt the desolate cliffs of Gehenna’s first layer like sentient columns of living steam.

Formed from an unholy amalgamation of misery, pain, hunger, sweltering heat, and poisonous vapors, a phiuhl resembles a swirling, churning miasma of green and violet vapors. With concentration, an onlooker can make out a roughly humanoid shape amid the chaos, with a suggestion of long, spindly arms or a hint of a leering, elongated face wracked with suffering.

Phiuhls normally travel in pairs, though that is the only hint of any sort of racial identity among them. Whether or not they draw sustenance from their predations upon mortals is a subject of much debate among scholars, who occasionally manage to trap one or two on the Material Plane for bizarre and twisted experiments. Phiuhls serve no master, however; their only goal seems to be to destroy any other kind of creature they encounter.

Phiuhls speak no audible language, but they appear to communicate with one another.

Combat

A phiuhl knows it can’t do much damage with its heat touch, so instead it prefers to fly above its enemies so that it can subject as many of them as possible to its death gas without risking melee. Thereafter, it swoops in for desiccating attacks until all its enemies have been destroyed.

Death Gas (Ex): Any creatures susceptible to poison within 50 feet of a phiuhl must succeed on a Fortitude save (DC 18) or take 1d10 points of Constitution damage immediately and another 1d10 points of Constitution damage 1 minute later (unless another DC 18 Fortitude save is made). Those who save against a phiuhl’s death gas are immune to that phiuhl’s gas for one day.

Desiccate (Ex): Any character in a square occupied by a phiuhl at the end of the phiuhl’s turn must make a Fortitude save (DC 18) or gain two negative levels. The saving throw to remove one of these negative levels also has a DC of 18.

Heat Aura (Ex): Anyone within 30 feet of a phiuhl must make a successful Fortitude save (DC 18) or take 1d6 points of fire damage. Treat this effect as a burst that continually radiates from the creature.

Gaseous Form (Ex): A phiuhl’s insubstantial form grants it immunity to critical hits. A phiuhl cannot run, but it can fly (slowly), and it is subject to winds. It cannot wear armor, manipulate solid objects, or enter water or other liquids. It can pass through small holes or narrow openings⁠—​even mere cracks. It also can occupy squares occupied by enemies (see Desiccate).

Inscrutable Mind (Ex): Any creature attempting to establish a telepathic link to a phiuhl’s mind (via detect thoughts, a psionic ability, dominate monster, and so on) must make a Will save (DC 14) or suffer the effects of feeblemind as cast by a 9th-level sorcerer.

Source: Fiend Folio, page 135. Changes applied as per the D&D^® v.3.5 Accessory Update. Removed the “immunities” entry from Special Qualities as no text in the Combat section of the description mentioned those additional immunities (other than acid, fire, and poison immunity mentioned elsewhere, and critical hit immunity from its gaseous form). This is presumed to be an error on the publisher’s part.