Invisible Stalker
This NPC can be found in Borean Tundra (73), Dragonblight (32), Stormwind City (16), Crystalsong Forest (14), Zul'Drak (10), Sholazar Basin (6), The Storm Peaks (6), Grizzly Hills (5), Icecrown (5), Wintergrasp (4), Strand of the Ancients (3), Howling Fjord (2), Magister's Terrace (1), Halls of Lightning (1), Durotar (1) and Arathi Highlands (1).