After you save the ship from Blackhorn and his drakes you parachute onto Deathwing's back and blast more armor plates off of him. This apparently will give Thrall a clear enough shot to be able to hit the non-armored part with a blast from the Dragon Soul.
The fight starts out pretty nicely with a cinematic. It's pretty spiffy the first time you see it, and I am happy to watch it in full when we go back for an fun night raid of DS, but the cinematic can get quite annoying when you're learning the fight. Especially when you're learning the heroic fight, where one missed dispell results in instant death for the raid. Of course those wipes were some of the most hilarious ever. Anyway, start the fight, get a cinematic of parachuting on to the dragon's back, which flows pretty smoothly into the whole raid parachuting onto the dragon.
Sky Captain Swayze yells: Don't worry about me. Stop the Destroyer! Enshu-falah-nah, dorini.
You land, and immediately need to kill three of the four corruption tentacles. Two of which seem to have grasped Swayze and Ke'anu. I don't know what Swayze is saying, but it goes pretty well with his Westfall Redneck personality. Anyway, once you kill the tentacles he flies off and as far as I know is never seen or heard from again.
Once on Deathwing's back, you're now in one of the most boring, yet burst dps stringent, fights of any raid I can remember. The raid needs to blast three separate plates off of Deathwing's back. The only difference in each of these three plate removals is the increasing number of corrupted bloods that spawn as the fight progresses. Deathwing doesn't even have any sort of new emotes as you move through the fight; he just recycles the same set of four phrases.
Deathwing yells: Your tenacity is admirable, but pointless. You ride into the jaws of the apocalypse.
When you get the final plate blasted off of his back you get treated to another cut scene. Thrall has apparently been paying attention to your fight. (Though not helping!) Once that last plate is gone he fires up the Dragon Soul and manages to peg the big angry dragon with it. Fortunately your raid somehow manages to jump out of the way in time and parachute to land on the rocks around the Maelstrom. Once down you get the Cache of the Aspects to loot.
Alexstraza yells: You have accomplished the imposible, succeeded where all Azeroth feared you would fail.
Alexstraza yells: Before you is the Cache of the Aspects. Take from it what you will, for you have more than earned the right.
Nozdormu yells: ...although, you may want to hurry.
I was super proud of the raid when we killed this guy, both on regular and heroic. Between the amalgamations, corrupted blood, rolling him, and the very strict dps check on the Burning Tendons it was an excellent triumph of coordination when he was defeated.