Will multiplayer games in Magic 2015 unlock cards?
Solution 1:
Yes - winning a multiplayer game does in fact reward you with a booster pack (by the looks of it, for your current plane / set in the campaign) - but the game doesn't make it very clear.
After winning a game, if you go to the Decks screen on the main menu, you'll see a new booster pack waiting for you to unwrap it. You'll then recieve a couple of cards in your card pool, to be combined into your existing deck, made into new decks, or just to read and enjoy.