This one should be rather simple as well, since mephits are fairly plug-and-play.
Smoke Mephit
Small Outsider (Air?, Fire?, Extraplanar)
Hit Dice: 3d8+x (x hp)
Initiative: +x
Speed: 30 ft. (6 squares), fly 60 ft. (good)
Armor Class: x (+1 size, +x Dex, +x natural), touch x, flat-footed x
Base Attack/Grapple: +3/+0
Attack: Claw +x melee (1d3+x)
Full Attack: 2 claws +x melee (1d3+x)
Space/Reach: 5 ft./5 ft.
Special Attacks: Breath weapon, spell-like abilities, summon mephit
Special Qualities: Damage reduction 5/magic, darkvision 60 ft., fast healing 2
Saves: Fort +x, Ref +x, Will +x
Abilities: Str x, Dex x, Con x, Int 6, Wis 11, Cha 15
Skills: Bluff +8, Diplomacy +4, Disguise +2 (+4 when acting in character), Escape Artist +8, Hide +12, Intimidate +4, Listen +6, Move Silently +8, Spot +6, Use Rope +2 (+4 with bindings)
Feats: 2
Environment: Elemental Plane of Air and Elemental Plane of Fire (?)
Organization: Solitary (1), gang (2–4 mephits of mixed types), or mob (5–12 mephits of mixed types)
Challenge Rating: 3
Treasure: Standard
Advancement: 4–6 HD (Small); 7–9 HD (Medium)
Level Adjustment: +3 (cohort)
Breath Weapon (Su): 10-foot cone of soot, damage 1d4, Reflex DC X half. Living creatures that fail their saves are blinded(?) for 1d2 rounds. The save DC is Constitution-based and includes a +1 racial bonus.
Spell-Like Abilities: 1/day--dancing lights (DC X), invisibility. Caster level 6th.
Summon Mephit (Sp): Once per day, a mephit can attempt to summon another mephit of the same variety, much as though casting a summon monster spell, but with only a 25% chance of succes. Roll d%. On a failure, no creature answers the summons that day. A mephit that has just been summoned cannot use its own summon ability for 1 hour. This ability is the equivalent of a 2nd-level spell.
Fast Healing (Ex): A smoke mephit heals only if in contact with smoke.