Single Player Adventure Mode Coming to Hearthstone: Heroes of Warcraft

Progress through each of the five unique wings of the dungeon and gain new cards for your Hearthstone collection by defeating iconic bosses
At PAX East 2014, Blizzard Entertainment announced Curse of Naxxramas: A Hearthstone Adventure, a single-player mode for Hearthstone: Heroes of Warcraft that offers 30 new cards as a prize for clearing areas and defeating bosses from the ancient necropolis Naxxramas, a base of operations for the powerful archlich Kel'Thuzad and his plague-bearing undead host. The completion of each of the five unique wings will reward you with a guaranteed new Legendary card.
Moreover, Curse of Naxxramas will have its own unique game board and will offer nine unique Class Challenges that will put your Hearthstone skills with a specific class to the test. If you're able to overcome the Class Challenges that face you, you will be rewarded with new class-specific cards to add to your collection.
Curse of Naxxramas will be implemented over the course of 5 weeks, opening wing by wing. The first wing of Curse of Naxxramas, The Arachnid Quarter, will be available free for all Hearthstone players. If you wish to venture further into Naxxramas to collect all of the new cards for your collection, each wing besides the Arachnid Quarter can be purchased with in-game gold or real money. As each wing is released, the cards available in each wing will also show up in your Arena picks, even if you have not earned them for your personal collection yet.