Well, that's my species.
We are a very varied bunch, even more so than the dragons. Appearance-wise we are reptilian, though that means any shape, species and combination. The reasons for this lie in our rather peculiar biology, why I had best cover from the beginning:
When an imp falls pregnant, which is often, she finds a host mother whose clutch she can hide her children in, hence that's why we're called cuckoo imps. Don't worry, we don't have the same fratricidal instincts. This mother can be of any species imaginable, though reptiles and human-like forms are most preferred. The trick of this is: we imp moms lay our eggs directly into the mother's body while she is already pregnant and sleeping. Usually she's none the wiser when she gives birth to more babies than she originally had. After all, doctors, wise men and so on can always make mistakes...
The baby transforms in the adoptive mother's womb into the mother's species. Ninety nine times out of a hundred that baby becomes an ordinary creature and their story ends there, imp-wise, other than a few odd 'reptilian' habits. The remaining one in a hundred though is a real imp child. That babe is always born from an egg, even from human parents. This is something of a giveaway to those moms and dads know of the imps. To others it's merely a blessing, a portent of greatness or some-such. Love (and for the more cynical of you, chemical/mental conditioning beamed straight from the egg) ensures the mother doesn't think her strangely born child cursed.
The imp child grows up as her adoptive species, albeit a particularly strong and healthy sort, loved by and loving her family with any luck (and it's very bad luck to get on the imps' bad sides by abusing one of their own). That is until puberty arrives, where the kid starts to emanate strong pheromones that make them rather irresistible to local reptiles, and feels a certain attraction to reptilian-kind. It's pretty inevitable that a 'forbidden' tryst will develop between the imp and reptile (of course, if the imp is already reptilian due to her adoptive mother being a dragon or similar, it's hardly forbidden, but those relationships are pretty simple and boring to recount so for now I'll stick with the alternative: human-like imp and big horny dragon).
Months after sex, usually when females are becoming heavily pregnant, they experience a rather fraught and confusing transformation that ends them up in a shape halfway between their normal form and the species they had mated with. From this point on, they become aware of their ability to change forms, willingly or in response to danger or lust.
So: what powers of transformation do we imps have? Well, let me first complete our life cycle. When a female imp becomes pregnant, and that can be from any reptile or human-like creature we mate with, we can choose between settling down and raising the children as our own, or (and I'm sure you won't like this idea) putting them up for 'adoption' in another mother's womb. Believe me, there are strong instinctive urges that compel us to do this. I have over two hundred children, not one of which I have raised myself. If you see me as an uncaring, irresponsible mother... well, maybe I am. That's why I leave my offspring in the loving hands of more capable moms. Maybe I shouldn't get pregnant? I have a species to continue, and that urge is strong as it should be. That's not to say I don't get lonely sometimes and wonder what they're getting up to...
So, back to our powers of transformation. While the basics (changing between adoptive and 'mated reptile' forms) are easy, we can learn to do much, much, much more. The next step may be to mate with other reptiles and learn their forms too, or to try stuff like slithering and see if our bodies adapt and make us into snakes. We gradually learn how to partially change, become non-reptiles, even objects. And still our powers are barely touched upon. The truly dedicated, lucky and clever become:
Cuckoo Imp transformation is extremely intricate, and changes are handled cell by cell. It is controlled by a fantastically intricate section of our minds. This 'second' mind is kept separate from our normal thoughts because of its incomprehensible power and emotionlessness. Basically it's a computer in our heads that takes our desires or needs and alters our forms accordingly.
In cuckoo imps this part of our minds never changes, no matter how much the rest of us does. After all, why would you risk losing its power and getting stuck in your current form? But if you truly need to, or want to, you can dare to use the power of the second brain to change itself, upgrade itself! And what do you do with this smart new upgraded brain? You use its incredible new power to devise an even better upgrade!
This upgrade process is without limit, giving royal imps an ability to transform which is equally without limit! Royal imps have the powers of gods, to do almost anything they want, their power unmatched by anything except gods and other royal imps.
If you must go and kill an imp, question whether you want royal imps to learn of this and come after you. And if you have to kill a royal imp, ask yourself why, and see if there's a more peaceful route. Did that fail? Okay, then: 1) Get another royal imp to bop him. 2) Shoot him and hope he's not bothering to protect himself, you might be lucky and he might be dumb. And 3) Make him fall into:
This is what I was named after, my parents having nearly fallen into it themselves, and me being the product. Imagine possessing all that power to alter your mind. Why, you could use it on your pleasure centers, make yourself happier than you've ever been. And why stop there? You could be on a permanent heroin binge that never ends or turns sour. And why even stop there? You could become so utterly high there's not a drug or experience in existence that could offer a millionth of the pleasure.
So you drop happily into the hedonism trap, continually increasing the ecstasy you feel, along with your body and mind's ability to handle it without shattering. Like a junkie, you withdraw from a world that offers nothing to compare with your permanent high. Sat there in the heart of a star, millions of feet underground or even pretending to be a statue in the local park you experience pleasure until the end of time, contributing nothing to the world's progress, and also not endangering it.
Many a royal imp has fallen victim to this, keeping our numbers in check, ensuring the evil (and therefore selfish) or careless disappear before they can threaten a world. And many a mortal has fooled a royal imp into experiencing the pleasure he never wants to leave, and in doing so rid their lives of a terrible peril.