More and more Mega Stones are being added to Pokémon Sun & Moon, giving players access to a wider variety of Pokémon Mega Evolutions. This latest distribution features Mewtwonite X and Mewtwonite Y, which will let your Mewtwo Mega Evolve into its two different forms. [Thanks, Serebii.]
To obtain the two Mewtwonites for yourself, simply enter the code M2DESCENT into your game on the Mystery Gift menu.
Pokémon Sun and Pokémon Moon are available for the Nintendo 3DS.