Xariona

Xariona is a level ?? rare outdoor boss with approximately 12.9 million health. She can be found in Deepholm flying extremely high in circles above the Temple of the Earth. She flies very quickly and can fly in both clockwise or counter clockwise directions. She is also notorious for getting Aeonaxx campers excited when NPCScan goes off.

As of patch 4.1 Xariona drops one guaranteed purple item. She drops Xariona's Spectral Gauntlets which are item level 359 mail physical dps gloves . She also generally drops about 20 gold, another epic item and some nice jewelcrafting designs. 

She is one of 5 rare outdoor bosses added in Cataclysm. There is one in each Cataclysm zone. All of these bosses are:

Akma'hat <Dirge of the Eternal Sands> - Uldum

Garr - Mount Hyjal

Julak-Doom <The Eye of Zor> - Twilight Highlands

Mobus <The Crushing Tide> - Vashj'ir

Xariona - Deepholm

In order to down her you are going to need at least a semi-decently geared tank, healer and a dps, although a full group is advisable if you don't want the fight to go on forever.

Xariona has a few abilities that you should be aware of before you start the fight.

Twilight Breath - Deals shadow damage in a cone in front of the caster. (2 second cast) She casts this about every 20 seconds or so, pretty easy to heal through.

Twilight Fissure - Deals shadow damage to any enemy within the shadow fissure after 5 seconds. (2 second cast) These are very easy to avoid. They look just like a dark void-zone on the ground, if your standing in it simply step out.

Twilight Zone - Creates a zone of twilight power. Reduces magic damage taken by 75% for all units within the zone. This appears as a white circle on the ground. The tank will need to stand in this for when she casts Unleashed Magic. The tank should only step out of this if Twilight Fissure is dropped in the same location.

Unleashed Magic - Unleashes twilight power to deal heavy magical damage to nearby enemies. (5 second cast) This spell deals 200k arcane damage, the tank must be standing in the Twilight Zone to survive this attack.

I've got a video below that shows the fight. Once you watch about a minute of it you can pretty much get an idea of what to expect as she just uses the same abilities over and over again. (I apologize for the jumpiness at the beginning, I had a lot running in the background.) The group in the video had 6 people in it, a decently geared dk tank, nubby priest heals, 1 decently geared hunter and warlock and 2 lower level melee toons who were leveling in the zone. Essentially the fight was 4-manned. The whole fight lasted about 5 and a half minutes.