Which is the hardest Boss in Highmaul ?

Well sorry for the absence guys, but I had to do some personal stuff and I didn't have any time for posting. 

The first post will be a question to all of you who like PVE. So my question is:

Which is the hardest Boss in Highmaul ?

In every raid there is this one boss which is just giant pain in the ass. So let me know which is the most difficult boss for you. On the left side there is a poll where you can put your vote.