UPDATE: According to an official post by Wizards of the Coast, the expansion will be available on October 21st for 400 Microsoft Points and will include:

Three new playable decks, including Tezzeret’s “Relics of Doom” Planeswalker deck, and Sarkham Vol and Jace Beleren’s decks
Three new unlockable cards for each of the eight original decks
New Two-Headed Giant co-op levels
Three new puzzling challenge levels

Just when you thought you were out… Wizards of the Coast FINALLY announced both new DLC entitled Duel the Dragon, and a title update which should fix the horde of bugs out there as well as offer a forfeit option to help minimize the quitting. Duel the Dragon will include three new decks, but no deck building will be part of it. There will also be 6 additional ladder levels and new challenges that go longer than a turn. You’ll also face off against the Dragon as the title goes. Duel the Dragon DLC will be available “soon” but supposedly the title update will be ready to download even sooner. It’s about time, WoTC; the problems have been going on too dang long now!