Doryanni keeps one shotting me in second phase at 20%

Ok so normal difficulty I’m at 800 health 600 ES.

I don’t lose health in this fight on attempts but 6 times in a row at around 20% he does a sweeping strike that covers the area and insta kills me.

It’s not lasers or spells. Or his slams. Or his air attack thing

Any ideas? It’s so frustrating unable to go to cruel… I thought I was going to one shot him

Any ideas? :/ can’t progress