Ghostrider of Karabor

According to a tale fabricated by a spirit who was none other than Teron Gorefiend, the remaining death knights knelt before him and offered their lives as a sign of loyalty, after which Teron killed every one of them. From the fallen death knights rose the Ghostriders of Karabor. After the ritual, Teron killed himself. They currently patrol the perimeter of Shadowmoon Valley, bearing Gorefiend's Truncheon. They can only be seen by equipping the Spectrecles provided for the Teron Gorefiend quest chain or the helms provided as rewards for it.

The Ghostriders follow a large circular route using the available roads in the interior of Shadowmoon Valley, and typically ride their route counter-clockwise. Since traveling the same direction would mean they'd have to be overtaken, the quickest method for locating them is to fly/ride the route clockwise.