Each brand new factory sealed booster includes 12 random cards per pack, including 1 premium foiled card!. The Opus III master set includes 154 new cards. This includes 60 common, 42 rare, 32 hero, 14 legend, and 6 starter cards.
The manufacturer has also confirmed that the 6 Starter cards will feature an alternate art version contained in the booster packs! Each booster pack contains 12 random cards from the master set, so you have a chance to get any of the cards in any booster pack.