Mastery is one of the four premade decks that can be bought for 2500 Orbucks in the OCCG store. It's the hardest deck to master out of the four decks, and substantially weaker in terms of ally strength; new players often choose this as their starter deck and later regret it. The main strategy incorporated into this deck centers around Adept Mage, which gains +1AP and +1HP from each action played (this is why the deck lacks substantial allies). If played correctly, though, Mastery is very powerful.
4x Adept Mage
4x Killer Wave
3x Mist Machine
4x Sneak Attack
Strong against: Weak allies, slow-developing decks (this deck needs a few turns to play out while the opponent develops their own deck).