The demonic cultivation master was furious with the way that he was being kicked around by Lex, who was young and weak in comparison to his former self, and in a fit of rage activated a sacrificial skill that will allow him to display power that surpassed that of the Mortal Realm.
It would allow him to display the power of an Ascendant Cultivator, which he once had, and surpassed his current physical limits after his cultivation had fallen.
Centuries ago a righteous sect had fought an all-out war against the Blood Moon Demonic Sect and were on the verge of destruction until a master swordsman appeared out of nowhere. He defeated all the elders and sealed them, then sacrificed his own life to seal the Blood Moon Sect's master.