A soul resonates
It was surprising at least.
Reigner didn't think that he would be able to perfectly utilize dreams and nightmares on the ancestor. He expected him to cause some problems, but what Reigner needed was just a small spar with him.
At the beginning, Reigner and Ho Ancestor fought in the reality.
However, the disappearance of the white snake was the beginning of Reigner's dominance. He brought both dreams and nightmares for the ancestor to feed on these. His energies weren't replenished immediately, but Reigner's recovery was greater than ever.
At this point, Reigner felt like he had to just behead the statue, but this was when the dungeon's influence kicked in. It totally took control over Ho Ancestor and began to use him to kill Reigner. The way the power affected him was kinda lame, though.
He was just like raging bull, constantly rushing at Reigner while spitting shit.