Rather than calling it a mountainous region, it would be more apt to call it a den of monsters.
Demonic flames filled the mountainous region. From their position far away, they could already feel the cold, devilish, and dark auras surging towards them. Everyone's backs grew cold as their hairs stood up.
The mountainous region was vast, and the terrain was complicated with mountains and valleys everywhere. It was pitch-black, and no one knew where Netherworld Realm beings were hiding in. Within the black fog, divine senses were impeded. If one stayed in there for a long time, one could easily become demonized. Once someone was demonized, all the soldiers present would choose to commit suicide rather than becoming the Netherworld Realm's lackeys.
"Let's split up and enter. Take your time to kill the Netherworld Realm beings; do not be rash!"