It seems if i keep log in into game more than 24 hours. Arena matches become bugged. The reason for this bug might be technical and not game mechanical.

 In my last arena battle my oponent skullcrown unkilable abillity didn't triggered. He was one shot by Bloodgorged. My Bloodgorged abillity enemies killed by this cannot be revived didn't triggered neither. Skullcrown got back to life, because shinesha was in same team. After it i couln't select attack on him, and he dieed because of aoe damage.