The encounters in Throne of the Four Winds take place on platforms in the sky. If you fall off the platforms due to mechanics or intentionally, the game is supposed to pick you back up and put you on the platform without a death. For the second encounter on Al'Akir, you move to a platform central to the initial four platforms used in the first encounter. When you haven't engaged the boss yet, if you stand too close to the edge you get launched off into the air and eventually get saved by this falling mechanic and placed back on the closest platform. However, if you position yourself at the edge exactly in the middle of the four platforms (with about a 10 degree margin of error) you will get launched to your death.
As a priest you can life grip a fellow raid member and both of you will get launched into oblivion. There is a slight grace period when you approach the edge that gives you just enough time to use your ability before you're launched. Furthermore, you can find a sweet spot just outside the margin of error, where you will get saved by the falling mechanic but your victim will not.
My raid group took a 10 minute break and we had a lot of fun with this last night. I imagine there are other places you can do this too.
I apologize for my terrible mspaint skills.
TLDR;
1) Be a Priest
2) Go to the right spot in Throne of Four Winds
3) Life grip a raid member. He dies, you live.