My Paladin brothers and sisters, let us bow our heads and pray - for this is the battle in which we prove our prowess. Indeed, here we shine, and bear the brute force of our enemies on our shoulders alone, allowing our comrades to do the best of works - the culling of these enemies of life itself. Keep your shield close, your sword in hand, look the beast in the eye and know that the Light has given you all that is necessary, all that is best, to conquer even the Aspect of Death. Cloak yourself in truth, carry the shield of the righteous, cast your final judgment on the ender of worlds and know that this crusade has come at least to its end.
We've used this strategy a couple of times now and it is pretty damned fool-proof. Once you get the flow of the fight down, prepare for achievement spam. I'll assume you know the basic flow of the fight as you can learn from WoWPedia, WoWHead or any millions of other sites.
1 Tank (preferably a Paladin, but most classes can handle it)
2 Healers (we used a Discipline Priest and Paladin)
7 DPS (if you can get a DK to DPS you can make phase 2 very easy)
Prime: Truth, WoG, Shield
Major: Focus Shield, LoH
Un-glyph'd Divine Protection is very useful on Impales but Glyph'd DP can be very useful to deal with Bolt impact, Tetanus and other raid-wide magical damage, it's a matter of what's more important to you and what's killing you.
Platform Order: Green (Ysera) > Red (Alextrasza) > Yellow (Nozdormu) > Blue (Kalegos)
The order of kill is as follows on each platform:
Corruption > Bolt > Limb > Hemorrhage > Limb > Blistering Tentacle > Limb >
Blistering Tentacle > Limb
The DPS benchmark is to make sure your raid can kill the Corruption before the Elementium Bolt lands. This ensures that you should only ever get 1 Impale per platform. This is crucial. As a paladin you CAN survive two per platform but you shouldn't have to as if you're consistently getting 2 Impales, the last platform will be troublesome.
So. You start on a platform, you can ignore the limb more or less, spread out a bit so people aren't standing in a line behind one another, and nuke the Corruption as soon as it comes up. Here is how you survive all the Impales:
Platform 1 (Ysera): Dream
Platform 2 (Alextrasza): Ardent Defender + Divine Protection
Platform 3 (Nozdormu): Guardian of Ancient Kings + Divine Protection
Platform 4 (Kalegos): Ardent Defender + Divine Protection
Bolt will be coming out very soon after killing the Corruption, so swap and kill the Bolt, then begin on the limb. Keep the limb below 75% - preferably right about 80% - until Hemorrhage happens. Take it slow - this is the mana-regen part for your healers, if you're standing around waiting, it's fine, let your healers get the mana back up, this is crucial with 2 healers, as the Tentacles will burn through their mana pretty fast and you really don't want Blistering Tentacles and Hemorrhage at the same time.
Once Hemorrhage goes down, swap and burn the Limb. Jump platform, repeat.
On the third and fourth platforms, you will have to deal with
Blistering Tentacles as Alextrasza won't help you on those two - leave at least your top melee DPS who loose the most by swapping on the limb while the rest of the raid swaps and kills the Tentacles. We leave our Rogue on the limb. Ranged starts with the furthest Tentacles, melee on the nearest, and you should swap and help as well. I use Hammer here to splash some damage onto the Limb.
You might need to use Divine Guardian or other raid-wide CDs here, especially on the second set of Tentacles if the DPS is slow on getting them down and your stacks get high.
On the fourth platform you will also have to deal with the Bolt impact (as you'll easily kill it without the impact on the other 3 platforms thanks to Nozdormu). What's important here is that the Corruption is killed as early as possible before the Bolt lands, preferably with 5 seconds to go so you can all get well far away from the impact point to minimize damage from the crash. If you find yourself dying to this over and over, you can even use Heroism on the Corruption to get through this part. We have our DPS save all their CDs and Trinkets on the third Platform to use on the fourth Corruption and that's usually enough.
After that it's the same as third - Limb >
Blistering Tentacles > Limb >
Blistering Tentacles. This one can cut a bit close with the Cataclysm timer.
Notice this whole time the only thing you've had to tank is the Corruption, survive the impales, and pick up the Hemorrhage for a couple of seconds before they evaporate thanks to
Kalegos' buff. There isn't a lot to tank and using two tanks is a massive waste. As you're tanking the fourth Corruption, you're likely to be closest to the impact point when it lands if your DPS is low - remember it is safe to use Divine Protection in that case. Don't be afraid to use it to save yourself as long as you're not tanking Hemorrhages or Corruptions.
This should never happen, but, IF YOU TAKE A SECOND IMPALE FOR ANY REASON, your only recourse is an immunity. Ardent Defender is part of your first-impale rotation, but you can use DivineShield or Blessing of Protection to survive it - hit the ability, taunt, wait for the debuff to run out, and cancel. You don't need to loose a melee to pull this off but the timing can be tricky. Remember you have 3 seconds to pull this off - plenty of time and GCDs.
The basic progression of this is to burn Deathwing, swap and kill the Elementium Fragments, burn some more, swap and burn the Elementium Horrors, burn some more, stop at 11%, deal with the second wave of adds, the second set of Terrors, then hit hero and burn to kill while ignoring all other adds.
The only thing you're needed for is to tank the Horrors. I pick both of them up right away and drag them into Nozdormu's slow-time puddle, our Frost DK taunts one off of me. The DPS jumps on that one and burn it super fast - Anti-magic Shell is more than enough to soak the few stacks of Tetanus. You on the other hand will have a lot of stacks of Tetanus by this time and will be chaining CDs to survive. I usually use Guardian of Ancient Kings here just as the first Terror Dies and keep a twitchy hand on LoH, AD, or anything else to survive the massive spikes of damage from the DoT. If you need to, you can have someone taunt off and kite the add for 2 seconds or so to let the DoT drop off but usually it isn't necessary. Play it safe, and you'll be fine.
The Horrors are really quite survivable - on the kill last week, I died to a Tetanus tick after the first set of adds died and our feral druid and DK tanked the second set of adds just fine - though we did use Heroism to burn the adds faster. Your only purpose in Phase 2 is to survive tanking one of the adds while DPS deal with the other.
Burn Deathwing to get him as close to 11% as you can, and stop. Deal with the second set of adds the same way and you're on the home stretch.
Once the second set of Horrors die, use Heroism if you didn't use it on the Horrors and just burn to kill. If a third set of Elementium Fragments spawn, ignore them and just keep burning. You can't survive the AoE damage sub 10% for every long with 2 healers.
Save Divine Guardian for when Deathwing hits about 6% health as the AoE damage spikes quite a bit at 5%. Chain Divine Guardian with other raid-wide CDs - we go DG, Discipline Barrier, Aura Mastery, our Boomkin starts to channel Tranquility and Deathwing is usually dead right about then. I throw in a Holy Radiance too because why the hell not. Remind everyone to use Dream if it's off cool-down at this point as well.
It's actually not a difficult fight to tank at all, despite my preamble. Once you get the order of kills and rhythm down, this strategy is very repeatable. The healing on the other hand is really intense and you will want to hug your healers the first couple of times through. But it is certainly not more difficult than 2-healing, Ragnaros I don't think.