The Day of the Dead event is now live, there are only 3 NPC’s involved with this event and all 3 can be found in any of the major cities graveyards.
The first NPC is Catrina, /dance with her for your achievement
The second NPC is Chapman, you want to buy the “Recipe: Bread of the Dead” and also an “Orange Marigold” or “Bouquet of Orange Marigolds”
The third NPC is hidden but near the other two NPCs, just use either of your Orange Marigolds to detect invisibility to see the Cheerful Spirit who will give you a quest to give him some “Bread of the Dead”. You can find the Ice Cold Milk from innkeepers/drink vendors and the Simple Flour from cooking suppliers near the cooking trainers, then simply return to the three NPC’s, bake your bread and hand in the quest for your temporary pet.

You can view Blizzard’s official Day of the Dead page here:
http://www.wow-europe.com/en/info/basics/events/dayofthedead/index.html