Invisible Stalker
This NPC can be found in
Borean Tundra (64), Stormwind City (25), Dragonblight (22), Crystalsong Forest (12), Howling Fjord (10), Zul'Drak (9), Blackrock Caverns (8), Sholazar Basin (6), Icecrown (6), The Storm Peaks (5), Isle of Quel'Danas (5), Halls of Lightning (3), Shattrath City (2), Magisters' Terrace (2), Teldrassil (2), Terokkar Forest, The Bastion of Twilight, Firelands, Tirisfal Glades, Grizzly Hills, Icecrown Citadel, The Veiled Sea, UNKNOWN.