Steam Siege is the last set to feature the card style used from "Black & White" to "XY", as the following set features the style of the original Base Set. It features the Mythical Pokémon of Kalos; Volcanion and Magearna. It contains six new Pokémon-EX, seven new Pokémon BREAK, as well as bringing back an older mechanic, dual types, which was last seen in the HS—Triumphant set.