Yak Attack

This achievement is granted by killing 15 or more attackers at Niuzao Temple in Townlong Steppes, all within 5 seconds or less. The mobs must be tagged by you or your group. The achievement can be completed traditionally, by actually tanking and AOEing down the mobs, but it can also (more easily) be completed solo, by leveraging [npc=61093]'s help.

Most likely, you'll want to work on this achievement as part of your dailies for [faction=1341]. The August Celestial dailies occur randomly each day at one of the four areas in Pandaria which are devoted to each celestial.

Niuzao Temple has six phases that I've seen, which I've given arbitrary numbers for convenience.

In Phase 1, [npc=61093] (the big yak) is stationary at the temple, and the daily quests on offer include Paying Tribute. You can't complete the achievement at all (with Niuzao's help) when the temple is in this phase.

Phase 2 has Niuzao endlessly charging around the temple perimeter. As he charges, he instantly kills any mobs that are in his way. If you've tagged those mobs, they'll be treated as if you killed them. The dailies available during this phase include Paying Tribute. Although you can technically complete the achievement during this phase, don't bother. It's extremely difficult and very unlikely to work as well as you think. (It's very hard to gather up 15 mobs in one place without dieing yourself.)

Phase 3 is the one you want. In this phase, Niuzao is also charging around the perimeter, but the dailies available include The Siege Swells. This phase includes far more invaders than the other two phases. It is quite easy to round up 15+ attackers on the northwest edge (not the corner, but the outside edge) of the temple. Make sure to tag them all with some sort of AOE ability, and get them in the way of Niuzao as he completes his circuit. You'll still take a ton of damage, so you'll need to time it right, and don't be surprised if you die afterwards.

Once I finally saw this phase for the first time (after over a week of August Celestial dailies), it took me exactly one try to get the achievement. Don't waste your time trying this when the temple is in the wrong phase (I spent hours working on it previously).

Phase 4 has quests including The Siege Swells, but Niuzao is stationary. In this phase, you can't get Niuzao's help with the achievement, but you may be able to leverage the larger amount of attackers to do it on your own.

Phase 5 exists while you do your initial questing around the temple, before the dailies unlock. Phase 6 exists briefly during the final storyline quest for [faction=1270], which opens up when you reach exalted with them. Phase 7 exists as part of one of the final storyline quests when obtaining your legendary cloak. None of these last phases are helpful for this achievement.

Note: the little mobs that spawn when you bomb the wagons do not count toward this achievement.

Incredibly easy if you have [item=86565] and you're not a tank class.

Just go in middle between 2 packs, sound the horn, position them all in the path of the Ox -> profit.

The achievement is very straight forward. Kill 15 Sra"thik attackers in 5 seconds.
Once you are at the temple, the temple grounds are surrounded by these creatures. There are 6 groups of Sra'thik spread out amongst the ruins. A larger group of close to 13-14 are on the Northwest portion of the ruins, 2 groups on the North east of the ruins, with the first group having 5-6 mobs, the second having 9-11 mobs. The south- eastern group has roughly 8 mobs. The final 2 groups are located within the temple closer to the middle with an average of 9 mobs per side.

Niuzao is a gigantic ox that runs laps around the outer ring of the courtyard killing anything in his path. This of course is the key to the achievement, as each mob has 393k health. Trying to lower each mobs health and keeping them crowd controled would be a monsterous undertaking, as each mob deals roughly 8-10k damage per hit and they hit very fast.

The hardest part about this achievement is the fact that each group of mobs is segregated by Niuzao sentinels, friendly npcs that basically taunt and kill your target as you try and pull the mobs in front of the ox. The amount of damage you do (or the amount of threat you have, to be more accurate) on the mobs affects if they will run past these sentinels or stop to fight them.

I spent an easy 4 hours attempting this achievement before I finally got it. Currently on beta there aren't very many people in these zones any more, so the respawn rate of the groups of mobs is incredibly slow. Once I tried an attempt and failed, there wasnt sufficant amount of mobs to go again for at least 10-15 minutes. This shouldnt be the case on live, as many people will cause the mobs to respawn faster.

The only position I found that worked was the northern most corner of the temple. You will find that every other area has limits as the mobs will reset as you're trying to pull all 15 mobs from a second group. As a ranged class this was somewhat easy, melee classes are going to have a hell of a time. As Niuzao was in the very middle of the courtyard I began to pull the mobs, I bound nether tempest (any DoT will work) and targeted all 9 mobs in the inner courtyard starting with the southernmost mobs (the northernmost inner courtyard group) and worked my way north. When all 9 were tagged I ran north to the group of 13-14 and pulled 10 of them, (as time allowed) and brought them all to the middle of the Niuzao's path. If it wasn't for iceblock and cauterize I would have died. You will have to find your own method for this particular part to stay alive.

Good luck!