Voidtalon of the Dark Star

Voidtalon of the Dark Star is a very rare epic mount. It is a purple recolor of the Flametalon of Alysrazor.

Source
The item is contained within the object "Voidtalon Egg."

The egg can only be encountered by entering the Edge of Reality from one of the portals (which are also labeled 'Edge of Reality' to denote where they lead) that randomly spawn in various locations around. Most zones in Draenor have three fixed spots where the portal can potentially spawn, with the exception of (which has five), and Talador (which has only two). The portals will close immediately once a player enters, will despawn if a player who already has the Voidtalon tries to enter it, and will despawn after a few minutes on its own if no one attempts to enter. Only one portal can be active in Draenor on any given server at a time.

Mount Journal
''Corrupted by the presence of the Dark Star in, the Voidtalons resisted being broken by the Shadowmoon Clan and were ultimately destroyed by. Only a single egg remains, lost in the void.''