To start with, the famous wickerman of Undercity will now have a Stormwind equivalent, maintained by the Gilneans. Alliance and Horde will have a chance to honor their own wickerman or douse the one that belongs to the opposing faction. In addition, you'll be able to go on a stink bomb run over Stormwind or Undercity, or clean up after the other sides' bombing. You can read up on all of these quests, which are dailies, in Allison's Hallow's End Achievement Guide.
The Headless Horseman will once again lurk in the Scarlet Monastery graveyard, with his usual outlay of rings, his helm (perfect for transmogrification), and his sword, all of which will now be ilevel 365. His Reins will also be a possible reward from the first kill each day, of course. Again, you can find a complete list of his loot in our Hallow's End Achievement Guide.
Tricky Treats, those annoying things that you couldn't destroy fast enough in years past, will now buy you stuff. Vendors this year will sell every single Halloween mask for two Tricky Treats each, and two different pets, the Feline Familiar and the Little Wickerman, for 150 Tricky Treats each. Tricky Treats will be awarded from various quests or Hands of Treats from trick-or-treat buckets in inns around the world.
The holiday officially starts Oct. 18, so get ready! There's lots of new stuff to do this year, and not much time to do it in, especially if you're not about to tear yourself away from BlizzCon, even for a flying horse.