Doppelganger

Doppelgangers are monstrous humanoids, infamous for their shapeshifting abilities that allow them to mimic almost any humanoid creature. They are lazy but cunning creatures, who kill or dispose of people then assume their place. While not downright evil, doppelgangers are extremely self-centered and liable to look down on their victims. They are believed to be an artificial race, created by some mad wizard and to this day have a fondness for working with the magically inclined; mainly being used as assassins or in elaborate plots to usurp power.

Physical Appearance
In their true form, doppelgangers appear as tall, elfin, gray-skinned humanoids, whose thin bodies make them appear, to human eyes, sexless. Even this form is deceptive, suggesting they are phyically weak, when in fact they are quite strong and agile.

Society
Doppelganger families tend not to be close; usually a male and female meet, engage in casual sex, then leave one another, with the female being forced to single-handedly rear any resulting newborns—who will leave their mother upon reaching maturity. Some however, form tightly knit family clusters, while others will mate with humanoids, taking malicious delight in using their spouse as a cover for their inhumanity. Children born of such unions have a chance of being a half-doppelganger.