Atziri, Uber Atziri, Uber Izaro, Shaper

I would make a bigger deal out of Uber Izaro's variable difficulty than just "weaken him." Uber Izaro 4 key and Uber Izaro 1 key are two very different beasts. Uber Izaro 1 key is easily the easiest boss among the 4 in your title, while Uber Izaro 4 key on bad days is significantly scarier than normal Atziri.