Insanity
Jason could already predict what Lux would do in the following three days because it was not really hard to understand.
Yet, despite having predicted that Lux would give his utmost efforts to become stronger in these three days, it was still unexpected to hear that the Lord of Death would kill his own people and their soulbonds to do so!
Showing no remorse, in the next three days, he killed the strongest opponents he could face and revived them as Undead before binding them to his soul.
Through this, Lux's strength skyrocketed to a whole new level than cultivating would allow him. His strength had reached an extent his vessel was barely able to endure but even then it was not enough for him.
As such, for three sleepless days, Lux killed, revived, and bound his own kind and their soulbonds.
It was as if he was consumed with the goal of defeating and killing Jason.