I was soloing this fight today when I noticed something interesting. When I got Shemazan Blightmark below 4500 health he started saving pips and casting Rebirth when he had not cast a heal for the entire fight. This would not seem noteworthy except that I was soloing both bosses - who each had 20,000 life - without the aid of a minion on my Death wizard. So, the fight took a long time.
I had to pop a minion when I got Shemazan down to 1800 health, killing him shortly after. After Shemazan died Popzotz Unlucky Day made critical casts on every, and I am not joking, every single attack. What is more, where I had blocked the the majority of his critical attacks before, I was unable to block a single critical after Shemazan died. Is this an undocumented boss cheat? He did use a vengeance aura but that was nothing uncommon from the rest of the fight. What strikes me as odd is that he had at least 8 more attacks and every single one was a critical and I was unable to block each subsequent one. Has anyone else noticed this?
below 4500 health he started saving pips and casting Rebirth when he had not cast a heal for the entire fight. This would not seem noteworthy except that I was soloing both bosses - who each had 20,000 life - without the aid of a minion on my Death wizard. So, the fight took a long time. 
made critical casts on every, 