I will be frank: Every death knight should have a solid goal to defeat Deathwing this expansion. It's not for the experience, it's not the glory, it's not even for the achievements. No, it's for one thing: It's for the tentacle sword. This baby is everything that one can aspire for in a WoW weapon. It's a sword. It can be transmogrified into our signature runeblade. It has an awesome creepy pet proc. What's not to love?
Of course, to get to the sword, you'll first have to take down four bosses, hope the sword drops, and then hope you win the roll against who knows how many other plate DPSers in the raid -- but hey, you have to start somewhere, right? Let's dive into the Fall of Deathwing.
To be frank, the most annoying part of the fight with Ultraxion, the first boss, is his trash. Dragons will fly in slowly from the skies above and must be pulled down where you can DPS and/or tank them. If you can get past that, Ultraxion himself should be a breeze.
Ultraxion is relatively easy for DPS. You just sort of stand in front of him and do your damage rotations. He does massive amounts of AoE damage, though, so don't be afraid to use your defensive cooldowns to mitigate some of that. Also, when he starts casting Hour of Twilight, use your Heroic Will (a button in the bottom center of your screen) to shield yourself. I'll usually wait until the cast is half over to hit it just to make sure.
Tanks have one more thing to worry about in Fading Light. This is a debuff that will kill you if you're in the twilight realm when it finishes casting. It also resets your threat and prevents you from generating threat for 10 seconds, so you and your fellow tank should taunt off each other as you each receive the debuff.
Once Ultraxion is dead, you'll board an airship and face Warmaster Blackhorn. As a melee DPSer and tank, you'll focus on the melee adds that jump on board the airship, followed by Blackhorn himself. The melee adds do frontal cone damage, so tanks, keep them faced away from the raid as much as possible, and DPSer, stay behind them as much as possible. They also Charge and do damage to everyone in the path of the charge, so be prepared to compensate or get out of the way for that. If your raid leader has set a kill order for the adds, be sure to follow it. There are multiple waves of adds, so tanks, be quick to pick them up when they land.
There is one final thing to watch out for during the add phase, and that is the Twilight Onslaught. From time to time, Blackhorn will order his drake, Goriona, to strike at the airship. She will fire an attack that will do massive damage to everyone in the area of the strike. However, you don't want to avoid this. Instead, you want to actively stand in it, because if you don't, the damage will strike the airship instead. If the airship takes too much damage, it crashes and you automatically wipe. Therefore, even you melee DPSers should not be afraid to break off from meleeing the adds to go stand in the giant purple swirling vortex that appears just before Goriona strikes. Tanks, you should, if possible, try to drag your adds over to the vortex, if only to encourage any melee DPSers to join you in standing in the vortex. The more people who stand in the vortex, the less damage everyone takes.
Blackhorn himself is arguably easier than his adds. He does a stacking sunder, so tanks, you may want to consider swapping every three stacks. Otherwise, the big thing to watch out for is his Shockwave. When he starts to cast it, get out from in front of him or it will hit and stun you. He will turn and target a DPSer to cast this, so don't get complacent and think you're automatically out of his line of fire. You may also want to blow some defensive cooldowns if his unavoidable AoE shout starts getting your health low. Also, stay out of Goriona's flames.
The Spine of Deathwing is arguably the hardest fight in the Raid Finder, if only because it still takes a bit of finesse to pull off. The object of Spine of Deathwing is to tear the armor plating off of Deathwing's back so that Thrall can hit his juicy center with the Dragon Soul.
You will start by killing one of his Corruption tentacles -- and only one. This is because each time you kill a tentacle, you will spawn a Hideous Amalgamation. This Amalgamation should be tanked near to Deathwing's armor plate in back.
Now, you do want to DPS the Amalgamation to low health, but you do not want to kill it just yet. This is because it needs to be turned into a bomb so it can blow off Deathwing's armor. You do this by killing the Corrupted Bloods that spawn, and then running the Amalgamation over their corpses so it can absorb the blood. Unfortunately, when it soaks in the blood, it gains a massive DPS buff, and it when soaks in nine of the bloods, it starts giving off waves of AOE fire damage. Once it starts giving off that AoE damage, it's become a bomb, and you'll want to kill it too. Don't blow your offensive cooldowns here, though; you'll need them more in just a moment. When it starts casting Nuclear Blast, back off, as it's getting ready to explode for massive damage.
Once an Amalgamation explodes, it will pry off a plate, which will then be barely held together by a burning tendon. This burning tendon must die before it finishes sealing itself back up, so blow your offensive cool downs here. If you're successful, the plate will fly off and you'll have to repeat the process one more time. Continue this process until all the plates are off and Deathwing crashes into the Maelstrom.
Tanks, in theory the DPS should be pulling the bloods to you, but if they don't be prepare to move the Amalgamation a bit to soak up all the bloods. Try not to soak up too many before it's ready to be killed, though, as you'll want to save your healers the trouble of healing through that extra damage.
Madness of Deathwing
The key to final battle of the raid is simple: Kill the adds, kill the adds, kill the adds. I cannot express enough how important this is. If you don't kill the adds, you will get overwhelmed. There are four platforms (one per aspect) to start the fight, and each platform goes more or less the same.
To start, you'll get the Mutated Corruption in the back of the raid. The Corruption will use Impale to cause massive damage to the tank, so use your defensive cooldowns to avoid getting killed, then have the other tank swap with you to prevent death. While you're killing the Mutated Corruption, Deathwing will fire an Elementium Bolt, which does massive AoE fire damage. DPSers, start DPSing it as soon as it arrives, and do not stop until it's dead.
Once the Mutated Corruption dies, you aren't quite done. Deathwing will then summon Regenerative Blood adds. As the name suggests, they do regenerate health if left alive too long. AoE them down as soon as possible.
Once the bloods die, you should then be able to DPS down Deathwing's main Limb Tentacle. However, you will have one more issue. Every once in a while, he will spawn Blistering Tentacles. These tentacles cannot be AoEed down. You must do single-target DPS to them to defeat them. Once Deathwing starts casting the final Cataclysm, pop your offensive cooldowns. You must defeat him before that cast finishes.
As soon as the Limb Tentacle dies, you'll head to a new platform to repeat the steps. Your raid leader should call out or designate the next platform, so follow your raid leader (or absent instructions from your leader, the crowd). Note that each platform is ruled over by a different aspect, and as soon as you defeat the tentacle at that platform, Deathwing will take that aspect out of the fight, and you'll lose their buff. This is why most raids do Kalecgos' platform last, as his damage buff is arguably the best for taking out all those adds.
Once all four platforms are defeated, you must fight Deathwing's main part one last time on the first platform. Again, he will summon adds, and you must take them out. The Elementium Terrors will specifically need to be tanked, and Tetanus will kill the tank if they aren't killed fast. If Nozdormu has a time vortex down, tank them in there to help yourself survive. Otherwise, all DPS should be on an add if one is up. When all adds are down, focus on Deathwing. If an add spawns again (and they will), get off Deathwing and focus on the adds.
If you can focus on the adds, congratulations. You'll defeat Deathwing! Now, to hope the tentacle sword drops!
Learn the ropes of endgame play with WoW Insider's DK 101 guide. Make yourself invaluable to your raid group with Mind Freeze and other interrupts, gear up with pre-heroic DPS gear or pre-heroic tank gear, and plot your path to tier 11/valor point DPS gear.