Xukong's words were enough to Alarm Lin Mu.
Lin Mu had see plenty of Unorthodox Technique and even had a few memorized. Despite that, he knew better than to use one. Orthodox techniques were those approved by almost all paths and the unorthodox ones were the opposite of that.
"What is a Caustic Nether Spring, Senior?" Lin Mu questioned. "Why is a technique like that forbidden?"
"The Nether Vitriolic Baptism is a Body cultivation technique that utilizes one's entire potential while levying the external powers." Xukong spoke. "But that isn't why it is forbidden." Xukong added.
"Then why senior?" Lin Mu questioned.
"The Nether Vitriolic Baptism Is a body cultivation technique that is not of this world." Xukong spoke. "Or rather, it doesn't belong to any of the normal immortal worlds." He stated.
"Not of this world?" Lin Mu was stunned.
"Yes…" Xiong confirmed.