General

Thanks guys, totally forget about those transcedence skills.

Watch the dr animation, alternatively, u can use the transcedence skill time distortion which effectively removes enemy buffs every 4 seconds including damage reflect if I'm not mistaken.

I just used shadow rain (the transcendent skill) and attacked as fast as I could with beta only. Worked for me

Try using the skill that makes you invincible for 15 seconds

The 1HKO comes from Damage Reflection.
Watch the DR Buff/animation carefully and when it runs out, kill him.