XY Breakthrough Booster Pack

Parallel Worlds: Two Paths to Power! 

An amazing discovery! Pokémon BREAK Evolution opens a new path to power that builds on a Pokémon’s existing strengths and creates all-new battling options! These new Pokémon BREAK come from twin worlds, home to Zoroark BREAK, Mega Mewtwo X, and Mega Mewtwo Y. One world of technology, one world of nature, and all the wonders of BREAK Evolution are yours to explore in the Pokémon TCG: XY—BREAKthrough expansion!

Description From PokémonCenter.com