Complete the DLC Single Player Campaign, Duel the Dragon.
Here are a few tips for each opponent:
-Sarkhan Vol's Cries of Rage deck is easily put down with Ears of the Elves. Pump your elves, play an Elvish Champion, and forest walk him.
-Jace Beleren's Mind of Void deck can be beaten with the Eyes of Shadow deck fairly easily. Terror his creatures and make him discard his hand and you'll control the game.
-Nicol Bolas can be defeated with the Mind of Void deck. Simply use Mind Erosions and Traumatizes until he runs out of cards.
You have many cards to help you run through him. Cancel, Dream Fracture, Condemn, and Persuade your way through his army until he drives his library into the grave.
I was able to defeat Nicol Bolas my first try without unlocking any extra cards for Mind of Void.