Unseen

Unseen were invisible mobs that haunted Raven Hill in Duskwood and the Ruins of Lordaeron in Undercity. They were neutral unless attacked, but since they were invisible to the naked eye most players were totally unaware of their existence. Warlocks who could cast Detect Invisibility, or other players using various means to detect invisible mobs, could see them. In addition, they did not become visible when provoked.

Since they were invisible and neutral, they were generally not a threat to players. However, to any class with an AoE spell they could be extremely dangerous as they were level 49-51 and Duskwood was an 18-30 zone, so any players who encountered them were very likely to be a much lower level.

Flares and tracking couldn't detect Unseen. The warlock's Detect Invisibility spell allowed anyone to see them, but mages who were invisible could also see them.