Lu Feng did not use an immortal energy shield just now because he wanted to test the defense of his physical body.
Now that his opponent was using illusions to obscure his vision, it seemed to be time to use the defensive spell known as the Primordial Qi Divine Body.
The Primordial Qi Divine Body was a defensive spell inherent to the Chaos Divine Formula cultivation technique, and he had never used it since mastering it.
Chapter 343