Reins of the Raven Lord summons Raven Lord, an epic ground mount that requires 150 Riding skill to ride. It looks like a hybrid between a raptor and bird, however, as a ground mount, it does not actually allow the rider to fly.
In the PTR/Beta you start with a Raven Lord on a Pre-made.
This item drops off Anzu, who is available to fight against in heroic Sethekk Halls for the Druid Epic Flight Form quest line.
The drop rate, according to external data sites, seems to be less than 1%.
Patches and hotfixes
Patch 2.1.0 (22-May-2007): Added