Hallo! My name is Sunkist and I'm a Resto Druid playing on the US PvP Ner'Zhul server. I've played wow since about a month after release. I've dabbled with other classes but the druid will always be my class of choice.
Now for some healing and general pointers about the fight:
1. Grid Users will want to add the following debuffs to their center icons in order to track them
Incinerate Flesh Legion Flame Fel Fireball
2. When you see someone with Incinerate Flesh, that person needs to receive as much healing as possible over 15 seconds. I'm not sure the amount needs to be 60k as sometimes we were able to remove the debuff within 3-4 seconds it seemed. But that person needs to have the debuff taken away or else some major raid damage will ensue.
3. Legion Flame is good to have on your grid especially if you're leading the raid. I'd usually call out on vent if someone needed to start running around to avoid the fire
4. Fel Fireball was only cast on our tank and only cast during our 25man attempts. This needs to be dispelled away immediately by a priest/pally. We had a ret pally with some quick fingers do it for us
5. The Chain of Fire spell wasn't overly devastating unless the boss also had his "Nether Power" buff up. So while it's a good idea to spread out for multiple reasons, fire on the ground, chain fire, etc. Not spreading out perfectly won't generally be a cause for a wipe
6. Purging of "Nether Power" is absolutely vital. Whenever a new mistress spawns out from her portal the boss will receive 10 stacks of a buff called "Nether Power." Each stack provides a 20% bonus to his spellpower and pretty quickly destroys both tanks and raiders alike. This buff needs to be offensively removed with a combination of spellsteal, purge, tranq shot, remove magic, and shield slam. 2 of our 4 attempts ended very quickly because we weren't aware of just how important Nether Power was.
7. Curses. I actually did a lot more removing of curses in the 10man and removed 0 curses during the 25man. Not quite sure why.
8. Spawns. If the range dps is high enough just have them handle taking down the mistress and infernals. If you want your healers to work a bit harder go ahead and let the melee go in and kill adds as well. The infernals also channel their hellfire and that can be interrupted.
That's really about all the nuianced things I can think of about the fight right now. I really should try and start making actual guides but for now I don't mind just putting in my own initial thoughts about fights after we complete them as they come out
P.S. I'm trying to get my hands on some Fraps to see if we can get some movie action jackson up in here!