Invisible Stalker
This NPC can be found in Icecrown (8), Icecrown Citadel (1), Isle of Quel'Danas (5), Magister's Terrace (1), Stormwind City (26), Borean Tundra (72), Zul'Drak (2), The Storm Peaks (3), Howling Fjord (11), Sholazar Basin (6), Crystalsong Forest (12), Dragonblight (18) and Halls of Lightning (3).