Okay, now that that's out of the way, let's quickly recap what exactly Duels of the Planeswalkers 2013 is. The first thing you should know is that it might be called "Magic 2013" on your platform. This is because it's got a lot of crossover with the Magic 2013 Core Set!
The core Duels of the Planeswalkers 2013 game has ten decks that you can play in regular matches and Planechase multiplayer against either the computer or your friends.
The Duels of the Planeswalkers 2013 expansion adds five new playable two-color decks, each corresponding with one of the Return to Ravnica guilds (Azorius, Golgari, Izzet, Rakdos, and Selesnya), along with new campaign levels and challenges. Like the core game, it's 50% until November 26 or 27, 2012.
And then there's the first Duels of the Planeswalkers 2013 Deck Pack, which has two new decks. They're not on sale, but they're well worth the price!