A mid-grade Twelfth Order formation could never be called impregnable.
Even if one existed, it would surely only apply to cultivators below the Mid Twelfth Order.
Even a formation cluster like the one in Cold Mountain Domain left its cultivators filled with anxiety when surrounded by Primordial Demons, fearing the formations might collapse at any moment.
And just as the Cold Mountain Domain cultivators feared, the Primordial Demons had indeed been constantly seeking ways to seize an opportunity and shatter the formation cluster of Cold Mountain Domain.
Like the "Anomaly" from before, as well as those Heavenly Chasm Demonic Beasts they had captured earlier.
Golden Ridge Hall's formation was connected to the Heavenly Dipper and Earthly Fiend of the Ninth Heaven. Logically speaking, unless the Ninth Heaven was destroyed alongside it, Golden Ridge Hall's formation would remain unharmed.
No matter how much damage the Golden Ridge Hall formation endured, most of it would be borne by the Ninth Heaven. Of ten portions of force that landed on the formation barrier, less than one portion would actually be shouldered by the formation itself.
That was why Zhong Tongxuan had been so confident, and why the other Golden Immortals had been willing to treat this place as their final sanctuary.
But that was merely common sense, while Chen Fei himself was an anomaly.
Golden Ridge Hall's formation could indeed transfer damage to the Ninth Heaven, but before the damage could be transferred away, it had to pass through the formation first.
Chen Fei had previously obtained two high-grade Twelfth Order inheritances, two of which concerned formations. This raised his understanding of formations to another level.
To break Golden Ridge Hall's formation, destroying it together with the Ninth Heaven was one method. Another was to sever the channel through which the formation shed