Invisible Stalker (Floating)
This NPC can be found in
Dragonblight (28), Icecrown (20), Howling Fjord (16), Black Temple (15), Shadowmoon Valley (8), Ulduar (4), Isle of Quel'Danas (3), Dustwallow Marsh, Dalaran, Eastern Plaguelands, Grizzly Hills, Mount Hyjal.