This small, cloud-like creature has a shape that resembles a cross between a dog and a fox.
Fog Hound (CR 1)
N Small outsider (air, elemental, extraplanar) Init +7; Senses darkvision 60 ft.; Perception +4
--- AC 17, touch 14, flat-footed 14 (+3 Dex, +3 natural, +1 size) hp 13 (2d10+2) Fort +4, Ref +6, Will +0 Immune elemental traits
--- Speed fly 40 ft. (perfect), grounded Melee bite +6 (1d4+1)
--- Str 12, Dex 17, Con 12, Int 4, Wis 11, Cha 11 Base Atk +2; CMB +2; CMD 15 (19 vs. trip) Feats Flyby Attack, Improved Initiative (B), Weapon Finesse (B) Skills Acrobatics +7, Escape Artist +7, Fly +17, Knowledge (planes) +1, Perception +4, Stealth +11 (+19 in fog); Racial Modifiers +8 Stealth when in fog SQ gaseous form, grounded
--- Environment Plane of Air Organization solitary, pair, or skulk (3–12) Treasure none
--- Gaseous Form (Ex) When a fog hound enters a space containing fog, it may choose to become gaseous, as per the gaseous form spell, as a free action. This effect ends immediately when the fog hound is no longer in an area of fog, but otherwise lasts indefinitely. The fog hound can dismiss this gaseous form effect as a standard action. Grounded (Ex) When not in an area of fog, a fog hound falls unless it is flying in a space immediately above a horizontal surface (either solid or liquid).
Hailing from the Elemental Plane of Air, fog hounds are slender, canine creatures made of semi-solid cloudstuff, becoming less substantial when exposed to fog and mist. Though smarter than an average animal, fog hounds are still beasts, having neither language nor culture.
Despite their extraplanar origin, fog hounds are found on the Material Plane with surprising frequency. On that plane, they are most often found in large fog banks rolling in off bodies of water, and in large patches of ground fog found in low-lying river valleys. Sages speculate that such large areas of fog generate a tenuous connection with the Plane of Air, one that fog hounds can permeate when in gaseous form.
The same rumors that hint at the existence of magical cloud islands inhabited by cloud giants also suggest that fog hounds can be found in such legendary locales. This could suggest that such cloud islands exist in areas where heavy fog is common, or that such islands are actually features of the Elemental Plane of Air. Until such an island is found to exist, either claim is mere speculation.
A 5th-level neutral spellcaster with the Improved Familiar feat can gain a fog hound as a familiar.