Originally Posted by
djriff
I really struggled with many of the same problems you are. I figured out a how to smoothly play the longer and longer we wiped though.
I did the fight as AS.
At the beginning of the fight stand on top of the summoner, like literraly inside of him. You won't pull until you attack. Open like normal with MB but cast SW: P before MB. Main reason you do this is that extra second is another chance to proc an SA and grant on orb. Being right on the add allows you to basically instantly generate an orb when an SA spawns.
When the boss spawns, I sit right on the edge of green and spam MB and my pet attack macro while clicking like a maniac where the boss will spawn. After MB is done, i'll apply SW: P and DP while moving up to the boss. From there I just continue my general rotation. When first imps spawn I'll toss out Cascade right as their coming down, usually ensures I get at least 10 hits because of bounce travel time. I immediately start running to bait the fel seeker (we have a lock portal setup we can use every other felseeker, really helps with DPS) and just SW: D snipe the imps. I've found that on the first set of infernals if you cascade the second they come out, it'll be up just in time for the second imp spawn. I just dot up the infernals with SW: P and maintain VT and SW: P on manno. I was fortunate enough that the infernals would live long enough for it to matter. If that's not the case with you (10 seconds+ alive) then just cascade and MB/Flay them until they die. Since the second set of infernals would make cascade go out of sync with imps, it's up to you on if you want to use it. If you aren't struggling with imp DPS then just use it on Doom Lords and Infernals until P3. Once you're in P3 and no longer have to deal with infernals just cascade and SW: D imps and DPS manno. That's really all you can do for this fight.
I highly recommend Glyph of Fade and reflective shield. Also as a shadow priest you can solo soak 3 gazes with dispersion, making p4 much easier on your raid.
Hope this helps and best of luck.
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There's zero reason your mages should be focusing infernals that are out of range. You and your locks/boomies (if you have them) can take care of them just fine and you'll all gain more boss DPS for doing so.