The Immortal Vanguard

It's quite likely that you'll get this achievement along with your first kill, as the leaders are the only ones in any real danger, and the fight fails if any of em die. The Dragonmaw Bonecrushers will only cast Fracture on the leaders (tooltip here is incorrect btw, it's 10% of the leader's health every second) and unless your tank dies, none of the other npcs should ever be targeted by the adds.

(On Heroic, there's a mob that needs to be protected to get the tower open, but you'll probably kill it on Normal/Flex first and just get the achieve that way anyway :) )

If you haven't gotten this one already, it's really not hard to do. Burn boss. The End. Win, collect achievement.

The only thing you need to do is to have your three leaders of your faction stay alive by the time Galakras is down. I believe the event resets if all three of the faction leaders die.

This is the only post Warlords comment here, and this is probably the easiest achievement to get out of the whole lot from 5.4 on. Which is when I earned it through some normal raids and LFR's.

Good luck to you. I even think that if you wipe once and then on the second go-round, and your leaders live, you will get it. They do respawn if they are killed by chance.

Blizzard always puts achievements in meta raid achievements like this; you do them by mistake.