Dehydration

Just before he splits, have someone click an activation crystal, which has about a 6s cast time. It will fill the room with lightning and kill all the globules. Achievement complete.

Added a screenshot to help those who are having trouble finding what items to click for this achievement.

Obviously it will take some time to get approved, and I hope they do approve of it.

Basically they are little red crystals on golden holders and they are spread all across the walls of the instance. Look especially near the holding/stasis pens for the bosses.

As you come inside the instance, make sure you take a good and long look at the female NPC standing at the very entrance. To her left (your right) will be this very sort of crystal. Once you start the instance by talking to her, she will activate it and bolts of lightning will pretty much kill everything (as you've probably seen). This same effect is achieved when you press any of the other crystals strewn about.

I just recently got the achievement and it took no time at all. The crystals activate instantly so, it should go quickly and smoothly.

Oh, its also a lot easier now as the crystals click instantly, there is no "cast time"