A trick or a test
Hao Xuan quickly closed his eyes to send out an army of spiritual threads after Mendax. A crystal clear image appeared in his mind of the scenes below, showing a river made entirely of Yin energy.
The Yin energy was strong enough even to freeze some of the spiritual threads but not before he got a good enough look at the monstrous creatures inside it.
At first glance they looked like 4-6 meter-long pudgy serpents swimming through the river of Yin energy at breakneck speeds but because of his supreme mental energy Hao Xuan was able to get a much better idea of their origins by plowing through his memories in the blink of an eye.