The Mauhúl valley is dotted with ancient ruins of a time when angels and their mortal allies battled an Abyssal invasion. In this Demon Spawn War (8972 GE - 9493 GE), the valley was of high strategic importance. Fortifications and Covenant armies blocked demon movements east and west, and continuously worked Bileddanul's rich mithril veins. The Covenant forces positioned in this valley were Turkûn serving under then archangel Naraz-Nâru. They battled the demon armies under Ahnuthall; who in turn answered to Orcus. After five years of hard-fighting, a special Covenant unit was deployed to this area. They were tasked with coming up with ways to prune their enemy's numerical superiority. This Covenant unit, the beginnings of the Blighters, developed a disease called the RT-12 Leech. Spreading by way of infected plants, the disease got out of control, wrecking havoc on both sides. Because of its virulence, and for the rest of the war, the valley was left abandoned.
Today, Mauhúl is a disease-ridden place of sickness and decay for only the hardiest of plants and beasts. Animals and beasts native to Mauhúl are of the Dire type, primeval in appearance, and often very aggressive.