Please help me beat great sage

Please give me any tips to beat him, all the online videos seem to be outdated. I once made him just to sliver of health. But idiot killed me with full health and after that I am no close to beating him. I am losing my motivation, never had I ever faced this extreme difficulties.

The arena makes it worse with its invisible wall. Sometimes I die just with directional dodge. Once I got stuck in between him and wall. I had experimented various builds chi build, mana build, spell binder, everything. I am at the point I wanna uninstall the game.

The game is extremely buggy. Animation lock, inconsistency in interaction in phase 1. The thing is I am not even sure if I could beat him.