Poison Mist

The Poison Mist is an orange, toxic mist that permeates both the Eastern and Western Plaguelands. Within 20 miles of Stratholme the mist becomes much worse. It is actually a supernatural poison, and only necromancers, members of the Cult of the Damned and non-breathing creatures are safe from it.

Speculation

 * In World of Warcraft an orange mist is indeed present in the Plaguelands, but doesn't seem as toxic as described in the RPG. It also has no name, even though Plaguemist Ravine may indicate that it could be called the "Plaguemist".
 * If it is indeed plague-based, the Poison Mist may be created by the plague cauldrons of the Scourge.