Mystic Peering Formation

As soon as he had arrived, he had seen the formation outside the Xuantian Dao Sect. That was what had enraged him the most.
Through this formation, they were able to observe every movement of the Xuantian Dao Sect. Although it couldn't see into the Xuantian Dao Sect, it was still a provocation and an insult.
This little move of theirs might not have affected the Xuantian Dao Sect on the surface, but if the Xuantian Dao Sect simply endured it, then eventually it would be surrounded by all kinds of formations. If it was like a game of chess, the end result would definitely be a checkmate.
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