Dopplegangers and Changelings

Dopplegangers are roughly humanoid beings spawned of the Daelkyr, which can change their form at will to appear as any humanoid creature with unnerving ability. This includes clothing and worn objects, though they are only facets of the design and will collapse into flesh when too far from the Doppleganger's psychic control. They are creations of the Daelkyr, as far as our scholars can tell, Vokollin specifically created the first, though his myth blends into many others.
Changelings can only change their bodies, and are born of a mating of a Doppleganger and a mortal. This is nearly never known by the mortal beforehand, until the baby is born without a face. This was common following the Doppleganger Crisis.