Only someone who possessed a fragment of his soul could refine the ring.
Upon seeing the contents within the ring, this person would undoubtedly be curious and study it, especially the cultivation technique in the jade slip, which even an ordinary person could read.
The Black Prison Sovereign had deliberately self-detonated his corpse pill before his death, sensing that this was a world devoid of spiritual Chi.
His corpse pill's poisonous gas would spread throughout this world along with the infusion of spiritual Chi, turning countless living beings into walking corpses.
In such a naturally advantageous environment, anyone who obtained the Demon Evil Art would inevitably cultivate it.
As long as they cultivated and absorbed soul power, the Black Prison Sovereign could use this to resurrect, completely kill the host, and take over their body for rebirth.