City: Winding Mountains and Miasmatic Valleys, a Gunman Suddenly Encounters a Dark Shadow

The miasma is shrouded deep in the winding mountains, and people are trapped in the misty valleys every ten days. The young man smashed dead wood and smashed boulders, and he boasted that he was invincible with his marksmanship. A black shadow breaks through the air. What is hidden in the deep mountains and forests?