The Valenar view the Mournland as a proving ground, and warbands frequently venture across the border to test their mettle. Quite a few do not return, but those who do are fully proven in the eyes of their comrades. Many who fail to return aren’t dead, but have in fact been corrupted by the Mournland itself. Something about the bloodlust of the Valenar seems to call to the magic of the region. The result is a community of creatures that aren’t quite Valenar any longer. They congregate in an area that the Valenar refer to as Taer Virduul, or “Camp of the Mad.” The riders of Taer Virduul are all insane, consumed with pure bloodlust. Their mounts suffer the same affliction, and indeed evidence suggests that the Taer Virduul elves might share an empathic link or even a primitive hive mind with their mounts. Elves and mounts both are cannibalistic and cruel, torturing captives and even eating them alive. They make clothes and armor from the flesh and bones of their victims.
If you have access to Heroes of Horror, apply the tainted raver template (page 154) to both the elves and their mounts. If not, simply assume that each is in a constant state of rage (as the barbarian ability), homicidal and chaotic, unable to be reasoned with.