Headless Horseman returns! Queue daily in the dungeon finder for a chance at the Headless Horseman's Mount. The Hallow's End festival runs till 01 November. Good luck!
Deathwheels and Dragons: The pre-Warlords of Draenor patch (6.0.2) has begun, and with it comes three new mounts: the Emerald Drake, which is a reward for the Awake the Drakes collection achievement, the Felfire Hawk, which is a reward for the Mountacular collection achievement, and the Warlord's Deathwheel chopper (Horde), which is free to all accounts that logged in by Sep 30. If you missed out, hopefully it'll become purchasable in the future, but we have no information on that yet. The Champion's Treadblade (Alliance) will definitely be for sale at a later point.
»Preview Upcoming Mounts
VALE: The new patch also heralds the demise of several mounts. The Kor'kron War Wolf and Ancestral Phoenixes sadly enter retirement. Hopefully they'll return in some form (possibly the Black Market Auction House) in the future. If you managed to obtain an ancestral phoenix on one of your characters, you should now have access to all four colours across your entire account.