The skies over Azeroth are soon to be ablaze with lighting, fire, and one massive dragon. Blizzard are releasing Nalak, the storm lord, onto the World of WarCraft's Isle of Thunder. Hatched by that meanie, the emperor Lei Shen, Nalak has been brought up on the taste of all the Azerothian(?) races, so if you want to get your hands some level 522 raid gear and some level 493 Tyrannical PvP gear you're going to have to fight tooth and nail for it.
Further details below.
The Isle of Thunder is seeing a couple of new areas added to its geography, a set of stages that must be completed one-by-one raid-style to access the next. The final stage, the central courtyard, contains the entrance to Lei Shen's citadel, oh, and that massive sky serpent. The one that shoots lightning.
Blizzard do say, mind, that you can try and run past Nalak and break for the citadel entrance but "[i]f you’re heading straight for the citadel, be wary of getting hit by one of Nalak’s damage abilities when he’s in combat!"
The new instance will arrive with Patch 5.2.0 which launches within the next two weeks.