Shadow Fey
The Shadow Fey are a species of darkness-loving, shadow-touched Fey native to the Demiplane of Dread, where they inhabit the dark faerieland domain known as the Shadow Rift. Originally slaves to a terrible demon-god from the Plane of Shadow known as Gwydion, a great hero of their people managed to lead them to freedom by finding a passage out of that dark realm and into the Demiplane of Dread. Which is the first time in history when getting stuck in Ravenloft was an actual improvement for anyone's lot in lives.
Shadow Fey are detailed in the AD&D sourcebook "The Shadow Rift" and in the 3.5 sourcebook "Van Richten's Guide to the Shadow Fey".