The Immortal of Huangshan thought, since Lin Fei was the Law Enforcer, and Dugu Aotian acknowledged him, he should have left him something formidable!
However, the Immortal of Huangshan wasn't aware that Lin Fei's supposed trump card was actually the Heaven and Earth Qi left to him by Master Qingfeng, power cultivated over five hundred years, sealed within Lin Fei. Lin Fei initially didn't know about it, but under Dugu Aotian's guidance, he learned to use this power.
However, this power is a one-time use; once used, it will deplete, and depletion means it will reduce, never to regenerate. In other words, if Lin Fei squanders this power today, he won't have it to face potential crises tomorrow, leaving him unable to solve problems on his own.
