For a limited time, you can get the items needed to evolve Mewtwo into Mega Mewtwo in Pokemon Sun and Moon.
Pokemon Sun and Moon players can now receive the special items needed to evolve Mewtwo into Mega Mewtwo X and Mega Mewtwo Y. The items are obtained via a special mystery gift promotion. Here's how you get them:
- 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 the code M2DESCENT
- Watch as you receive Mega Stones!
- Speak to the deliveryman in any Pokemon Center to pick up your Mega Stones.
- Be sure to save your game!
While Mewtwo can't be caught in the Alola region right now, these items will work with any Mewtwos that you have transferred over from prior games using Pokemon Bank. Nintendo haven't stated how long this event will run for, but it will only be a limited time.