Invisible Stalker
This NPC can be found in Borean Tundra (63), Dragonblight (32), Stormwind City (22), Crystalsong Forest (14), Icecrown (9), Blackrock Caverns (8), Sholazar Basin (6), Howling Fjord (5), The Storm Peaks (5), Wintergrasp (5), Strand of the Ancients (3), Zul'Drak (2), Grizzly Hills (1), Halls of Lightning (1), Orgrimmar (1) and Firelands (1).