defeated a champion

Ranshahar5

It's been a long time since I've been trying to defeat the champion in story 1, act 6, round two. The champion has the ability not to be damaged by 10%. To cancel the ability it is written that it is required to dodge special attacks. I did everything I could and nothing helped. I'm really discouraged and don't know what else to do to move forward. This champion is preventing me from progressing in the game.