Theres a whole lot to digest between the Invocations, the new Afflict mechanics (which is a modular and keyworded version of [casthaven]Vedalken Ghoul[/casthaven]s ability), the evolution of Exert to tap abilities, the awesome design of [casthaven]The Scorpion God[/casthaven], and the Gatewatch losing their first big fight
Therefore, you cannot use the mutate abilities of creatures you already have in play
Remember that practice makes perfect in this aspect as well
Keeping aggressive artifact creatures safe from combat damage enables incredibly powerful attacks and forces your opponents to make hard decisions since they can never trade on defense
The rebalanced Boros Energy deck is still one of the strongest and most-played decks in the format, but instead of dominating, it's now a peer among several other powerful decks, like Mono-Green Elves, Izzet Wizards, and a few different takes on Mono-White