From the Burning Crusade bestiary:
Warp stalkers are crafty, predatory hunters indigenous to Draenor that have been corrupted by the Burning Legion. Some reports even suggest that Legion officers employ the stalkers as mounts, utilizing the creatures’ uncanny abilities to phase in and out of the physical and astral dimensions at will. Unbound by the constraints of physical reality, these powerful, mystical creatures often range far and wide: almost no realm is out of reach.
Warp Stalkers have been found in Terokkar Forest. Apparently their constant blinking around disturbs magical energy, making them an annoyance to magic-users.
Warp Stalkers have also been found to be beasts tamable by hunters. They possess the skills Bite, Claw, and their species skill, Warp, which instantly flings them forward 30 yards towards an enemy when used.