"But then the barking of dogs fills the air, and the host of wild souls sweeps down, fire flashing from the eyes of the black hounds and the hooves of the black horses"
Kveldulf Hagen Gundarsson (Mountain Thunder)

(drawing by Ari Berk, after R. W. Feachem).
http://www.orkneyjar.com/tradition/hunt.htm
http://en.wikipedia.org/wiki/Wild_Hunt
The people of the mounds are important in this lore,especially in regard to Utiseta,in lands where there has been cultural crossover/syncretism between Celt and Norse customs. [Utiseta:the practice of sitting out overnight on a longbarrow mound.]
"In the testimonies of many rural folk a distinction is often made between the sidhe who are seen walking on the ground after sunset, and the 'Sluagh Sidhe', the fairy host who travel through the air at night, and are known to 'take' mortals with them on their journeys. There are also guardian sidhe of most of the lakes of Ireland and Scotland. These distinct categories of sidhe beings ties in with the testimonies of seers who divide the sidhe into wood spirits, water spirits, air spirits and so on, the elemental spirits of each place."
http://deoxy.org/h_mounds.htm
http://en.wikipedia.org/wiki/Sluagh

More later...Hag riding and Black shucks next...