[X] Close in, relying on Sixiang to keep it's toxic aura from affecting you, between your music and your subordinates ritualism, it should be possible to pacify the creature.
[X] Go in for the kill, and call Zhengui to help. You have underestimated your own killing power before, and the things cultivation is not superior to your own. Hill or not, you can End it.
[x] Continue distracting the hill beast while your subordinates and Zhengui wall off the remaining exits from its valley, then vanish, and only engage again if it looks to be breaking out.