So. Me and my buddies were just doing ICC25 heroic. And I was in charge of jumping to the other ship; completely normal, right? We aren't meant to do the achievement, ridiculous to try it on 25 hc. So how did we get it?
Basically, once I hit him, I went back to the ship. To the edge. Saurfang did not reset yet. So I was like, "okay, let's see what happens, make this a tad harder, more % damage." So I threw Heroic Strike at him.
He actually began WALKING towards our damn gunship. In midair he vanished and appeared again on his ship. I conituned throwing stuff like Taunt, and suddnely, he walkeed .. and appeared on our ship! Oh shit. We went and continued to attack him until 50 stacks, where our tanks got oneshotted. Suddenly, Muradin tanks him! Both unable to die. We were like "Uh .. okay rofl." DPSed the ship down, all adds getting owned, the 3 dps that were on the ship just afked there and killed the mage, and we got the achievement.
So, from what I can speculate, basically this is a bug, most likely an AI improvement (and in icc de-improvement) in cataclysm expansion. So he tries to cross it; basically, it's preferred that maybe a ranged would do this. Leap onto the enemy ship, hit the boss and grab a good aggro, run back, go to teh most edge, and continue nuking the hell out of him.
Eventually he'll appear right next to you; run to Muradin, and let him grab aggro. (Kinda not as effective now in cataclysm, but many, many people are going for the achieve. And you can make this even easier with this .. exploit? Is this an exploit? I assume it's exploitation of a bug .If it's an exploit, do move it. I can't really tell if it is or not.)
Enjoy your achieve.