Here are the methods to defeat Blade Berserker:
Method I: Have Ironclad and Sylph draw Blade Berserker's attention. The rest should enter the Gate of Remembrance, defeat the inner demons surrounding Bai Jian, and rescue her. Victory will be achieved without direct confrontation.
Method II: Send a few high-DPS allies through the Gate to protect Bai Jian. The rest should engage Blade Berserker head-on.
Method III (Not Recommended): Ignore Bai Jian's fate and engage Blade Berserker in his frenzied state with full force.