A grand total of 134 cards are planned for the set, including four old gods (C’Thun, N’Zoth, Yogg-Saron, and Y’Shaarj) and several familiar NPCs with new madness-flavored twists. The full extent of the expansion mechanics have yet to be revealed, but you can be certain that there will be randomness and a great deal of calling upon the power of the aforementioned old gods. Check out the trailer for the expansion just below.
Source: Official Site