Root Fire, also known as Source Fire, was a heaven-defying Supernatural Power possessed only by Tribulation Transcendence Stage cultivators. Simply put, it bore some similarity to a True Spirit's Origin Body, and under ordinary circumstances, it would absolutely never be used no matter what.
Only when there was no other choice, such as when one's life was threatened, would one ignite Source Fire. It was somewhat like drinking poison to quench thirst, yet it could make one's magic power and cultivation surge by a large margin out of thin air in a short period of time.
However, the consequences were no small matter. At best, it would damage and consume a great deal of Life Origin Qi, requiring ten thousand years of secluded cultivation to recover. At worst, one's realm would directly fall, changing from Tribulation Transcendence to a Spirit Division-level cultivator.
Moreover, after this sort of realm drop, cultivating back up again was as hard as scaling heaven. If one wanted to step into the Tribulation Transcendence Stage once more, the bottleneck's shackles would be several times harsher than back then.
If it merely consumed Life Origin Qi, then that would be one thing. With the long lifespan of a Tribulation Transcendence Stage existence, ten thousand years of seclusion was not necessarily unacceptable.
But the danger of one's realm falling, and the immense difficulty of cultivating back afterward—this point made any mighty expert shrink back at the sight of it. Unless it was a life-or-death moment, they would absolutely never ignite Source Fire.
Lin Xuan naturally understood the gains and losses involved. However, when he had been facing Yellow Springs Ghost Mother, Lin Xuan truly had no better choice.
The Five Dragon Seal could not be used lightly. Only by igniting Root Fire could he use the True Spirit