Hello,
there's a tip how to one man+ Omen [Lunar Festival Boss] http://www.wowhead.com/?npc=15467
Achievement: Elune's Blessing - Achievement - World of Warcraft
You gonna need:
1. HUNTER
2. Some good mobile dps if you don't wanna spend ages on it, because he got 5.5m hp
How to do it:
It's very very easy. Hunter will use Aspect of the Cheetah and kite him around shrine, while dps are just smashing him. That's all, hope you got it, i can prove it with some SS.
Screenshot: