When Leng Yan and the others were still alive, they were already experts at the Golden Core Stage. After becoming fierce ghosts, they were even more powerful than ordinary fierce ghosts. Therefore, Li Mochen and Leng Xiaoyo were no match for them, even if any one of them fought alone against them.
As a result, they proposed to be sparring partners for Li Mochen and Leng Xiaoyao.
Leng Yan would practice with Li Mochen, while Chi Feng would practice with Leng Xiaoyao. Except for ensuring that they wouldn't be disabled or killed, they would go all out, because only in this way could Li Mochen and Leng Xiaoyao really improve.
If they stopped short of the goal, what was the difference from not practicing at all?
Without pressure, there was no resistance. Without a crisis, there was no giving it your all.
