Valadar Starsong in Moonglade (53,35) will give you the quest. He also sells festive pant suits or festive dresses. This is pretty simple, although you'll need a raid to do it. Most can complete it with 10 level 60+. It's a simple tank and spank fight and he only hits for around 3k on a tank. He does have a Cleave ability that is avoided by standing behind him and an AOE Starshard spell. The Starshards hit for 3k a second and can also be avoided by moving out of the visible radius. However, he does have 5 million HP, so it's not a particularly quick fight. You don't need to be grouped with those who started the fight to get credit. Simply stand on his dead corpse to receive the blessing. In order to summon Omen, you need to use Cluster Rockets on the Southeastern shore of the lake in Moonglade. Omen's minions will appear and you need to start killing them. Continue to fire off rockets and kill the minions till he appears.