From discussion with a few other warlocks, it appears the fight is bugged to hell. If you are fully mutated and have immolate on any add (red or black), it will take an obscene amount of extra damage. (appears to be 3-4x as much) During re-re-progression on the fight (fucking fun blizzard), it wasn't uncommon to put immolate on an add, to then one shot it with chaos bolt. When we killed it this week, I wasn't aware chaos bolt was hitting higher because of immolate, hence less immolate damage on my end. The other warlocks in my guild were completely out of the know (lol)
From our logs, you can see that his average chaos bolt is hitting a lot higher than mine. His immolate uptime is also a lot higher than mine.
http://www.worldoflogs.com/reports/r...e/?s=379&e=848
I'm preparing myself for a third round of progression on this retarded boss when they change it again next week.
Note: Chaos bolt is obviously not the only thing getting damage buffs. 800-900k conflag crits were pretty often happening, as well as ~600k incinerates.