The Nether River Horn that Li Yelai acquired in the wilderness is suspected to have come from Disaster Fog No. 18.
It appeared after the Era of Calamity as a wandering type of disaster fog.
It failed to devour a large number of intelligent beings to become a Forbidden Zone, but it's still extremely dangerous, roaming the world.
The high walls of the Giant City can isolate the disaster fog, but in the wilderness, the disaster fog is an unstoppable Catastrophe.
Humans or other intelligent beings devoured by it cannot leave the disaster fog. Unless someone succeeds in conquering it.
Disaster Fog No. 18 has swallowed several official caravans and many scavengers in the North, even lingering around the Forbidden Zone, devouring many Forbidden Zone Creatures.
Several Northern Giant Cities dispatched a large number of elites, and even a Human Supreme intervened to completely conquer it.
And within Disaster Fog No. 18 is the Nether River.
