This monster originally appeared in the Modern Reference Document.
A huge discoloured cloud breaks suddenly toward you, from beneath is voluminous bulk writhe four dripping tentacles.
ACID RAINER (CR 8, 4,800 XP)
N Huge outsider (air, elemental, extraplanar)
Init -2; Senses darkvision 60 ft.; Perception +13
-- Defense --
AC 21, touch 6, flat-footed 21
(-2 Dex, +15 natural, -2 size)
hp 105 (10d10+50)
Fort +8, Ref +7, Will +7
Immune acid, elemental traits
-- Offense --
Speed fly 40 ft. (perfect)
Melee 4 tentacles +16 (1d4+8 plus 1d4 acid plus grab)
Space 15 ft.; Reach 15 ft.
Special Attacks acid spray (DC 20)
-- Statistics --
Abilities Str 26, Dex 7, Con 20, Int 6, Wis 11, Cha 11
Base Atk +10; CMB +20 (+24 grapple); CMD 28 (can't be tripped)
Feats Fly-By Attack, Lightning Reflexes, Lunge, Power Attack, Vital Strike
Skills Fly +15, Knowledge (planes) +11, Perception +13, Stealth +11; Racial Bonus +8 Stealth
-- Ecology --
Environment Plane of Air
Organization solitary, cloud (2-4) or storm (5-16)
-- Special Abilities --
Acid Spray (Ex) Once every 1d4 rounds, an acid rainer can spray out a caustic mist that fills a 30 ft. rafius spread centered on itself. Each creature within this radius takes 2d6 points of acid damage. A successful Reflex save reduces the damage to half. The save DC is Constitution-based.
Acid rainers float among the multitude of clouds in the Plane of Air. Somewhat less intelligent than air elementals they behave in are more animal-like fashion. They often group together for protection and hunt in packs to ensure success. Since they do not eat, the hunting practice seems to be some sort of ritualistic behaviour for the acid rainers. Acid rainers and arrowhawks often fight for territory.
Purple Duck Notes: In the Modern Reference Document these creatures are known as Acid Rainers. If I was planning on using them in a fantasy game I would probably change the name to something like caustic clouds.