The ninth boss battle in Tomb in the Sky took place in water.
The majority of players were not accustomed to aquatic battles. Due to this reason alone, Tomb in the Sky's ninth boss was considered even more difficult than the final boss.
Fighting a boss in water was different than fighting players in water.
For PvP, it was fair for both sides. The hindrances from water would affect them equally, but it was an entirely different matter for bosses. For shameless entities like bosses, who had the system's backing, water would not affect them like conventional logic would entail.
In the water, the movements of players would become slower, but bosses could freely move around, as if they were dragons soaring through the skies. It would be strange if an opponent like this wasn't difficult to deal with.
Ye Xiu wasn't surprised Seven Blossom Leaves and the other Knights couldn't fight aquatic battles well.