"Accidentally Entering A Domain" 

The whole mountain was strange, as if it attracted spirits to come from far away and any animals who died in this place would definitely turn into spirits. 

Or when they stepped foot into this mountain, they became spirits. 

Other humanoid races weren't affected, and sacred beasts were also unaffected, but other beasts, monsters, and ordinary animals were affected. 

As if to prove this conjecture, at this moment, when everyone was confused about the strange mountain, a bird-type beast suddenly passed by the sky of the mountain right above everyone's heads. 

But then, out of the blue the passing bird suddenly became more transparent, and then the whole body turned into a spirit on the spot, not even leaving a corpse behind! 

Everyone saw this passing bird and saw with their own eyes how this bird turned into a spirit in the blink of an eye.