C149 Nine Revolutions Corpse Nurturing Formation

When An Yifeng's group of four arrived at the corpse aura emitting from the mountain cave, they were all stunned by the scene before them. The black gas continued to fly out from the cave and slowly floated up into the sky.

How many corpses would be needed to release such a dense corpse aura? Just by looking at the color of the corpse aura