Aether Mist

This is inspired by a famous monster in a storybook that I love. I've never used it in a game, as a feared legend. They have a weakness but you need to have read the story...or if you haven't read the story, just make up your own.  

Aether Mist

Large Sized Outsider
Hit Dice: 20d10 (150 hp)
Initiative: +2
Speed: Fly 50 ft (perfect)
AC: 42 (+30 natural, +2 Dex), 42 touch, 40 flat-footed
Base Attack/Grapple: +19 / +0 (Can not be grappled or tripped)
Attack: Automatic Hit (40-AC dmg)
Full Attack: Automatic Hit (40-AC dmg) or +33 Penetrating Attack (5-50)
Special Attacks: Automatic Damage, Double Damage
Special Qualities: Astral Jaunt, Immunities, Dmg Reduction 20/Adamantite, SR 35
Saves: Fort: -, Ref: +14, Wis: -
Skills: Knowledge (Astral, Magic, Religion) +20, Perception +40
Abilities: Str 28, Dex: 14, Con: -, Int: 10, Wis: 10, Cha: 10
Environment: Deep Ethereal, Aether Domains
Organization: Solitary
Challenge Rating: 20
Treasure: None
Alignment: Neutral
Advancement: 25 - 50 HD (Huge)

An immense sized, deeply coloured mist.

These living clouds are approximately 30 feet in radius and 10 feet high. Their origin is somewhere in the deep ethereal. They come to prime worlds when summoned by spell casters using a Monster Summoning VII or greater spell. Spell casters must sacrifice a single magical item worth at least 75,000 g.p.  which is consumed in the casting.

The only other time they can be recruited, is in the minutes after they have successfully completed a mission, they can be requested to stay and complete another mission if a Diplomacy check of DC 30 is made along with the offering of a magic item or gem worth at least 25,000 g.p.

The Ether Mist has never communicated with any other creature. When summoned their instructions must be exactingly precise, or they will interpret it sometimes with dangerous effects. If they have a weakness, it is unknown to scholars.

The colour of its mist determines purpose, when they have a new mission, they change colour.
Grey - guards an item for ten years; they pursue if the item is stolen
Red - Executioner, summoned to execute one creature on that same plane.
Purple - guards a location for ten years unless password is spoken

Combat

An ether mist doesn’t attack, just like a swarm, anytime creatures are in it’s radius, they are automatically crushed.

Swarming: An Ether Mist automatically hits all creatures that is within their radius. They inflict 40 - Victim’s Touch AC every round acting as a +4 weapon. All creatures affected must make a winded check (Fort DC = dmg taken) to remain fully active. If they fail, they are winded and are able to take partial actions for that round and any round they fail their save when in the misty cloud.

Penetrating Attack: This is a focused attack on a single creature, doing 5-50 crushing damage, acting as a +4 weapon. They can take this attack action even if they are using their swarming action, but only one creature is attacked in this manner. Victims cannot be the target of both the penetrating and double damage attack on the same round. A penetrating attack is most done on the second round, if a particular foe seems to have taken less damage than the others,

Double Damage: The Ether Mist on any round can designate any one creature that has taken damage from its swarming as it's primary target. This primary target must save vs a Fort DC 25, or take double damage from its swarming affect. A Red Ether Mist will always use this special attack on their target. They do not stop their crushing until the target is a blood smear.

Astral Jaunt: Ether Mist can re-enter the astral plane as a free action from anywhere. Any creature in the mist at this time must make a Will DC 33 or be transported to the ethereal plane at the same time. Creatures transported do not take swarming damage in the ethereal. It takes one hour for the Ether Mist to come from the astral plane to a material world, and can only be done in specific locations, such as a wizards lab or church with an active obelisk,, etc.

Immunities: Immune to mind-affecting spells, elemental effects, energy effects, poison, sleep, paralysis, stunning, disease, death effects, necromancy spells or any fortitude or wisdom save unless it affects objects. They are not subject to critical hits, subdual damage, ability damage, ability drain, energy drain or massive damage.