Evil techniques are so termed precisely because both the gains and the dangers of cultivating them far exceed those of orthodox methods. The "Record of the Primal Python Swallowing Thunder" places extremely harsh, almost perverse, demands on its practitioners, requiring an incredibly powerful physical body to directly swallow lightning like a primordial beast.
As for Violet Thunder Essence, it is a highly concentrated product of the lightning essence of the Immortal World. Even for a True Immortal, let alone anyone lesser, directly swallowing it could lead to instant death. Furthermore, it contains the power of heavenly tribulations; once it enters a human body, it doesn't just damage the flesh—it ravages the soul, the Dao heart, and even one’s fundamental destiny and luck.
Fortunately, Chen Xuan’s physical body is far stronger than that of other cultivators at his level, and he has cultivated the Emperor Star Tyrant Body and the Calamity-Free Sword Body. The latter, in particular, allows Chen Xuan to break through bottlenecks without hindrance while ignoring all forms of tribulation. Thus, cultivating the "Record of the Primal Python Swallowing Thunder" and swallowing Violet Thunder Essence is a viable path for him.
Chapter 4663