Hanging out in Moonglade, he's a real pain. Before you even think of killing him, you need to get to Moonglade first. Since I mainly roll with my warrior when attempting new things, I wasn't able to just take the easy way to Moonglade and teleport myself there. However, many thanks to Toast who filled me in on a little tip: talk to the Lunar Festival Night Elves in any major city to get a scroll that'll teleport you to Moonglade. To get the scroll all you have to do is complete a quest that has you light off a few fireworks that you can purchase from a near by vendor. Easy as pie.
Once you arrive in Moonglade, head up to the northeast corner of the map, in particular around coordinates 53, 35. You'll find the quest "Elune's Blessing" from Valadar Starsong, giving you the task of killing Omen for some handy rewards.