Nefarian Guide

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A fairly challenging encounter, perhaps the hardest before heroic. 1st phase , you get down in the arena and, and no, you are not fighting Nefarion yet, you start on Onyxia 1st. Nefarion will join the fight a bit later on. Onyxia does the classical cleave and tail swipe, but at the same time she has a lightning type ability. When the tank sees her sides sparkling, that's the time to turn her around because she does lightning damage to her sides. Raid get a tail swipe, but it's better then the lightning.
Additionally you will get a couple of adds. We tank and slow them on 25 man, and in 10 man we cc them. The adds have an energy bar that steadily drains. That's their life time. Tank or cc them until their energy bar becomes depleted. Keep them off your main tanks, they become reactivated if they get hit by shadow breath.
30 seconds into the fight and Nefarion joins in. Tank him on the other side of the platform, as far away from Onyxia. They get buffed if within 60 yards of each other. Onyxia has an energy bar that steadily grows. When it reaches 100% Onyxia will explode killing your entire raid. Your goal is to kill Onyxia before she explodes, but at the same time you want to put as much damage on Nefarian as you can. The more damage you put on Nefarian now, the easier it will be in the final phase.
Nefarion has a deadly Eloctrocute ability which will strike every 10% of his health. This ability does 80k damage to everyone in raid and adds 25 energy to Onixia. Call it out every 10%. Healers should have everyone full on hp before each 10%. But they can use mana efficient heals afterwards. At least in phase 1.
Before you get Onyxia down and finish up phase 1 you should aim to have Nefarion below 80%. Ranged can put dots on both targets for some extra dps.
Going into phase 2 and lava floods the room. You are to split your raid into 3 groups, each on a different pillar. Melees take care of the adds while ranged do damage to Nefarian. Stay spread out on the platform in 3 groups to minimize shadowflame damage. The adds don't need to be tanked but they do have a cast that does 40k aoe damage.This cast needs to be interrupted for the duration of phase 2. It goes of every 12 seconds in 10 man, so you need at least 1 interrupter per add in 10 man, and it goes off every 6 seconds on 25, so on 25 you need at least 2 interrupters per add. Almost everybody that can interrupt should interrupt in this fight.
And the interrupt issue brings us back to the beginning of phase 2, when the lava was just filling up the room and the adds were appearing on the platform. The thing is that the adds to their cast almost as soon as they spawn. So what you've got is ppl in the lava or just coming up from the lava, all burning up trying to get on the platform, with half hp , barely alive and then a blast wave hits them in the face and kills em. For me this is the hardest moment of the fight.
It is really important that you get that 1st interrupt. The lava is burning you up, the add on top ready to blast. I will not lie to you I missed the interrupt the 1st 3 times, yes I am human , yes I make mistakes. But I learned from those mistakes, and I developed a system, and after that I stopped missing interrupts. So here is how it goes: lava comes up, i'm jumping. Add comes on top of the platform. I select it even if I'm still in the lava. I'm focusing on jumping and getting out but my main priority is that interrupt.