"This is probably the hardest boss of this expansion (at least p1) and a pretty good ending of the MoP soloing in my opinion," Raegwyn noted on his video of the boss take-down.
So what's the master soloists's trick? As it turns out, practice. "Practise, Practise, Practise..." he wrote on the Blizzard forums, outlining the determination that led him to put in some 70 to 80 attempts at Dark Animus phase 1 and another few trial runs on phase 2. "I remember a time when i also was a noob as DK and then i soloed Hellfire Ramparts when i reached 60 on wotlk releaseday. ;D jk But for real im doing this kind of stuff since 2007. practise is the way to perfection and perfection isnt as hard to reach as you may think."
As Raegwyn claims: "And remember... What doesnt kill you gives you Vengeance."