Strange creatures from somewhere else that make magical things, do odd things and are not very good at looking like things. They try to look human or elvish or whatever but are just not very good at it. Ears at different heights, wrong number of fingers, two left feet and other such flaws. They also can't tell apart humanoid types and will say shit like "hello fellow humans I am a human like you and would like to be directed to the nearest alcohol drinking station" despite being in a room full of dorfs. When they think their cover is blown they run away. If they can't run away they'll twist time and space to findmake a new direction to run in.
They are tolerated because they don't harm people that anyone has ever seen and they make sometimes usful magical things like a harp that unspoils nearby food when played.
Nobody knows where they come from or where they go to. Nobody knows what their true form is or even if they have one. Nobody knows what, if anything, they are trying to accomplish. They're just there, being weird and socially awkward.