Two of the most prominent categories of fairies, derived from Scottish folklore, are the division into the Seelie Court and the Unseelie Court.
The Unseelie (Unholy) Court consisted of the malicious and evilly-inclined fairies. Unlike the Seelie Court, no offense is necessary to bring down their assaults. As a group (or "host"), they would appear at night and assault travelers, often carrying them through the air, beating them, and forcing them to commit such acts as shooting elfshot at cattle. _Wikipedia