C405 Yin cave

He didn't know what it was, but he knew that purple black thunder. If he remembered correctly, this purple black thunder contained a brutal energy that even a Xiantian master couldn't withstand!

What kind of existence was the Yin Grotto?

Why was there a seal? Why would there be a Yin Spirit? Why did hell's inferno appear, along with this mysterious circular altar that was pitch-black in color