Just a quick note to the above solutions regarding the strategy fighting Sorin Markov.
I tried different decks and strategy's while fighting Sorin including White, Black, Elves, Claws of Vengeance and the dragon deck (forgot the name), but the deck that is probably the most useful is the new mono red deck.
It consist of mostly spell (instant & sorcery) cards (seriously, go check it out!), so whenever Sorin plays a monster card you just use a spell card to counter that. On my first try with this deck I completely steamrolled him by just using spell cards and one monster card. Give the new mono red deck a try if your struggling with Sorin Markov!
To clarify: I won with just a 'clean' deck, no extra cards unlocked. (Thanks to G0RILLA FINGER)