Phiuhl

The phiuhl takes form in the volcanic furnaces of a lower plane, where magma gives the only light and the air is thick with heat and acid mist. Mercenary fiends call these creatures vaporous horrors, and other natives call them lingering deaths. Each is a tall, churning pillar of steam laced with sickly green and violet fumes, holding a loose humanoid outline. Misty arms stretch toward prey, and two black hollows serve as eyes.

No god claims them, and they ally with none of the plane's other powers. Scholar fiends and mastermind fiends have tried for ages to capture and study them, while devils and demons have tried to draft them into their armies; nothing has worked, and no force, bargain or spell holds a phiuhl for long. One cambion sorcerer tried ESP to learn the truth. Before his mind broke completely he muttered about 'undead lords of brass', 'spirits of long-dead wind dukes' and a 'melded prison of steam'.

Simply standing near a phiuhl is dangerous. Any creature that can be harmed by poison gas and comes within 50 feet must save every round or collapse from the fumes, then dies in 2d4 rounds. Within 10 feet, its heat deals 1d6 damage to anything vulnerable to heat, with no save, although a ring of fire resistance or similar protection helps.

In melee it swings two steaming fists for 1d10 each. That damage is mostly heat, so heat-immune creatures shrug it off but still face its other effects. A target hit by both arms is drawn inside the vapor and held. Each round thereafter the prisoner automatically takes 2d10 from the arms plus the 1d6 heat aura and loses one experience level as the phiuhl feeds. Escape takes either the creature's death or a successful bend bars/lift gates roll.

Heat, fire, poison and acid do nothing to a phiuhl, lightning deals half damage, and only weapons of +2 or better touch it; everything else passes through. It has 25% magic resistance, rising to 50% against spells that affect the mind. Its thoughts are so alien that anyone who reaches it with ESP or other telepathy must save vs. death magic or go permanently insane. Wind wall keeps it back, and gust of wind deals it 3d6 damage. Spells that assume a living physical body, such as finger of death, hold monster, grasping hand and slow, fail entirely. Controlling magic like charm monster or domination that gets past its resistance lasts only half as long. Some call it an undead elemental, yet no priest has ever turned one.

Phiuhls haunt the steam vents of their plane, mostly on its volcanic upper layers, though hunger can drive them down to the lowest. They usually hunt in pairs, moving in tandem to pin prey between them, and a rare band of two pairs is a true terror. A lone phiuhl is one that has lost its partner. Over the years it slowly comes apart, as if the pairing holds it together: it has half the normal Hit Dice and deals half damage, and saves against its fumes gain +3.

Rarest of all is a group of three, whose third member is a harvester of flame. A harvester is a smaller, red-tinted figure of steam carrying less poison and more heat, sometimes with a glowing red-white sphere in its chest. It has no gas cloud, but its heat aura deals 2d6 and its fists 2d10 each. It can also hurl a steam jet as far as 150 feet for 6d6 damage (save vs. spell for half). Creatures immune to heat still take half damage from a harvester, and those that merely resist heat take full damage. The harvester cuts foes down while its two companions drain the fallen. It never appears except with exactly two ordinary phiuhls.

To a phiuhl, everything living is food. Powerful fiends resist its attacks better than most, yet they still dread its level drain and its immunity to control, and anything with a mind fears the harvesters.

Night hags occasionally strike brief deals with a pair, trading larvae for safe passage or a small favor, such as holding off some pursuers. A lone steam mephit sometimes trails a pair as well, helping bring down prey and then scavenging any treasure. The phiuhls may not notice it at all, or more likely they ignore it as harmless, since they have no interest in treasure.