Invisible Stalker
This NPC can be found in Borean Tundra (64), Dragonblight (32), Stormwind City (16), Crystalsong Forest (14), Zul'Drak (10), Icecrown (9), Howling Fjord (8), Sholazar Basin (6), The Storm Peaks (5), Wintergrasp (5), Strand of the Ancients (3), Grizzly Hills (1), Halls of Lightning (1) and Durotar (1).