This is one of evolved or adjusted creatures I use instead of what`s in the books. It is a combination of the Imp and Mephit in terms of abilities but the background makes it a whole lot more interesting I think. Instead of a pesk to kill, or a evil sidekick , these creatures have the potential to be a troublesome but useful pain in the butt. Everything else not mentioned below, I don`t really worry about. They might have treasure or work in pairs, but mostly they are a curious dungeon dweller who may be an uneasy partner with your PCs.
Nyssian Imp (Long-Tailed Imp)
There are many gray-beards who will tell you what something is without ever having to step outside their Tower. Imps are beings from other worlds and they are vile, disgusting things without honour or virtue yet many adventurers speak of these things with grudging respect having been places where the only thing to give aid is the lowly important. They despise beauty or the fey, yet they will often lend a hand for the right price or favour.
Description: As younglings, they start at 3 foot tall, gray or blackened skin, small wings, long tail, sharpened claws. They grow into gargoyle-like beings, the easiest way to discern the difference between is a longer prehensile tail ending with a stinger. Imps often wear robes or cloaks to hide their appearance. While they prefer dungeons they do sometimes interact with city-folk especially when hired as guides.
While they were descendant from outer world version, these Imps are more mischievous trouble-makers than malevolent purveyors of evil. Their aim seems to be to get what they want with as little effort as needed and to mock those who do harm to creatures smaller then themselves or anyone who would treat ugly creatures badly. They are often mistaken for evil by other creatures. Larger, much more powerful evil creatures seem to assume a Nyssian Imp will obey their orders, and indeed they often will until its no longer convenient for a long-tailed imp to do so.
2 HD: Invisibility 5 rounds, Poison Tail Dmg d3, DC 13 (Paralysis d3 rounds), Ignore Magical Wards or protections. Two claw attacks every round doing1d4 damage. Add skill points every level as a ranger.
Typical Ability Scores: Str 8, Dex 17, Con 10, Int 13, Wis 8, Cha 13
Skill Bonus: +8 to fly rolls, +4 to stealth
Racial Skills: Bluff (Cha), Climb (Str), Diplomacy (Cha), Disable Device (Dex), Escape Artist (Dex), Fly (Dex), Knowledge (dungeoneering) (Int), Knowledge (local) (Int), Knowledge (local) (Planes), Perception (Wis), Sense Motive (Wis), Sleight of Hand (Dex), Stealth (Dex), Survival (Wis), and Use Magic Device (Cha).
3HD Sneak Attack +d6, Shape Change (1 creature)
4HD +1 to natural AC, Radiate Non-Detection
5HD Poison DC +2; Breath Weapon 2d8 (acid, cold or dust) DC 13 for half dmg 3 / day
6HD +1 to natural AC, long-Tail, Improved Claws, Medium Size
7HD Improved Shape Change (Up to four distinct animals), Improved Invisibility (5 rounds)
8HD +1 to natural AC; Sneak Attack +2d6
9HD Longer-Tail, Enhanced Claws
10HD +1 to natural AC; Breath Weapon 4d8 (acid, cold or dust) 3 / day, DC 16 for half dmg
11HD Poison DC +4
12HD +1 to natural AC; Sneak Attack +4d6
13HD Greater Invisibility (10 rounds, 3 / day)
Invisibility: A Nyssian Imp can stay invisible for short non-consecutive up to a certain number of rounds.
Ignore Magical Wards: Imps can ignore magical protections without setting them off. They either bypass fully or they do not go through, no middle ground and do not try or test as they seem to have an instinct that they do not test. The avoidance property is only for themselves, they cannot retrieve items from behind a barrier or ward. Their ability is only for magical wards, they must still find a way to get around standard locks and barriers.
Radiate Non-Detection: Eventually Nyssian Imps cannot be detected by spells or spell-like abilities until they reveal themselves. Once they attack or otherwise make contact, then spells for creatures in the immediate vicinity have the capacity to discern their location.
Improved Claws: Improves to 1d6 damage
Enhanced Claws: Improves to 1d8 damage
Longer-Tail: They gain an effective 10 ft reach with their long tail.
Breath Weapon: They can blast off a breath weapon of a particular type, once this is chosen, does not change. It does damage in a ten foot wide range out to forty feet away. They cannot add breath weapon damage to their backstab rolls.