The Legendary Pokémon Mewtwo is already formidable in battle, but when it Mega Evolves into Mega Mewtwo X or Mega Mewtwo Y it becomes even more powerful. And now you can get Mewtwo's Mega Stones in your Pokémon Sun or Pokémon Moon game via a special code. Give Mewtwo either a Mewtwonite X or Mewtwonite Y to hold to have it Mega Evolve two different ways during battle.
Mewtwo Mega Stones code: M2DESCENT
Mewtwo itself won't be found in the wild in Pokémon Sun or Pokémon Moon, but you can bring it into Pokémon Bank via Poké Transporter from earlier games. Pokémon will lose their items in the process, so currently this is the only way to get Mega Mewtwo X or Mega Mewtwo Y in Pokémon Sun or Pokémon Moon.
To get Mega Mewtwo's Mega Stones:
Select Mystery Gift on the main menu.
Select Receive Gift.
Select Get with Code/Password, then Yes, and then Yes again to connect to the Internet.
Enter your code.
Watch as you receive Mega Stones.
Speak to the deliveryman in any Pokémon Center to pick up your Mega Stones.
Be sure to save your game!
Have fun with your first opportunity to battle with the awesome Mega Mewtwo X and Mega Mewtwo Y!