It's like a mass of pure yin energy, often produced by practices in the dark arts or found on skulls and yin ghosts.
And the skeleton ghosts naturally endowed with rich yin energy in the Ancient Yin River Dao almost always manage to produce Yin Essence Pills.
So where are the most skeleton ghosts found?
Xu Qing instinctively thought of his old neighbor, the Du'e Ghost King.
"Twelve years..."
Xu Qing's eyes flickered. In twelve years, even if Zuo Zixiong and the Eight Banner Marshals could not defeat the Du'e Ghost King and the Yin Erosion Law King, it was enough to severely deplete his old neighbor.
In the thousand-year-old Ghost King Mausoleum, just how many fallen skeleton ghosts would there be?
Those skeleton frames are all stark white corpses!
And they can continuously provide Xu Qing with supplies of Yin Essence Pills.
"Xuan Yu! I've thought of a solution!"
As the moon rose high, Xu Qing turned his head to look.
He saw no black cat beside him to share his worries.