Patch 4.3.0: Hour of Twilight contains the Dragon Soul Raid and three new Caverns of Time 5-man heroics, and is the end of Arena season 10. This is the largest content release since the opening of Cataclysm.
At the peak of his insanity, Deathwing the Destroyer fought to drive the world into twilight - a devastated future bereft of all life. The Dragon Soul, a powerful artifact lost in the past, was the only weapon capable of truly stopping Deathwing, and so the guardians of Azeroth - the Dragon Aspects - sent a number of valiant heroes racing through time to retrieve it. Despite being attacked by the mysterious Infinite Dragonflight as they travelled the timeways, the champions returned the artifact to the present and delivered it to the wise shaman Thrall. With his aid, the Dragon Soul was deployed against the Destroyer during a brutal battle that began in Azeroth's skies and continued into the roiling heart of the Maelstrom at the center of the world. Through the combined efforts of the Aspects and their allies, the madness of Deathwing was finally brought to an end.