Apparently there was a quasi-exploit Horde-side where you could skip to the end of Mythic Daz'alor and only fight Jaina Proudmoore. Surprisingly, instead of removing the skip, Blizzard added an NPC for both sides that takes you directly to Jaina. This is unlocked if one character in the raid has beaten Mythic Jaina previously. This has become the newest activity in organized raiding, farming Mythic Jaina for the Mythic-only mounts.
Jaina drops two mounts for the raid, distributed via Personal Loot to people who don't have the mount yet.
The factor that makes this really viable is that there is a "cheese" strategy where you only have to do Phase 1 on the boat. You then run to Jaina, and do not interrupt her cast. Instead you just dps as hard as you can and you kill her before the cast ends. Now, at the end of expansion, a geared raid can do enough damage to make this viable.
The hard part, though, is having everyone in the raid avoid interrupting. Somewhat ironic, given all the trouble it takes to get people to interrupt when necessary.
Our guild decided to try this out after our alt raid. We only had about 10 guild members online, so we had to PuG 10 others through Party Finder. Our first couple of attempts went somewhat badly, as we had to learn Phase 1.
Then we got through to the second phase. But halfway through a PuG hunter accidently fired Countershot, interrupting Jaina's cast and putting us into the next phase where she promptly wiped us. Everyone was very unhappy. Our raid lead started insisting that people remove their interrupts from their bars, to eliminate even the possibility of interrupts.
The next attempts went pretty badly, wiping on the boat, and half the PuGs left. We replaced the PuGs and tried again. This time everything went cleanly and we got to Jaina. Everything was going smoothly, until one of the new people accidentally interrupted the cast!
After more insisting on removing the abilities on the bars, we tried again. This time was a great attempt, everyone got to Jaina alive, and we just grouped up and cleaved down people who got frozen. We beat the timer, defeating Jaina on that attempt!
Two of the PuGs got the mount.