The Children Snatchers

The Children of Green Mountain are told only tales only of the Mysterious Duergar who supposedly live in the deepest depths of the Mountain. They are sad that if a child doesn't do as they are told or goes to a place they aren't allowed, the Duergar come to steal them in their sleep. They apparently use magic to conceal themselves as they climb across the ceilings of the stone rooms and passageways. There were confirmed Duergar many years ago but they haven't been sighted recently, but the parents still use this method to maintain some order and discipline form their children. But who knows I haven't seen all of the caverns so maybe there are Duergars living in the deep...