What we know:
There will be a 10man and a 25man version, but no heroic modes.
The Ony Mount has an equal chance to drop from 10man and 25man.
The chance for the mount to drop is about as big as the chance of "being struck by lighting on a sunny day and attacked by a shark, all while in the presumed comfort of your own living quarters" .
Loot items will be of the same item level as stuff in the Colliseum.
Loot will look like the orginal stuff that dropped of old version Ony.
About the fight:
Phase 1: point her to the back wall and get her down to 65%.
Phase 2: kill first wave of whelps, ranged dps kill Lair Guard, don't stand where you can get hit by deep breath (frontal attack). Phase ends at Ony health 40%.
Phase 3: she lands, and belts out Bellowing Roar. Make sure to finish adds, threat is wiped from phase 1, keep tremor totem and fear wards up. DPS her down.
General: DON'T STAND IN FIRE YOU NUMBWIT!
Loot Table on MMO-Champion