I spent 3 hours learning the proper timing so you can kill them right at the start of Ch11. The trick is to stagger it, burn it down to a hair above where it transforms and switch to a non-damage paradigm. Then at the last possible split second before the stagger ends switch to COMx3 and have everyone blast it with Smite for the kill.

When I tried to kill them straight up at the start of Ch11 I was using SEN,MED,RAV/COM and was still getting whooped. When you get bellow 10% HP they could one shot my SEN through all of their defenses. Booo!