Pokemon Sun and Moon has finally dropped and Pokemon.com has released info on how you can obtain Mythical Pokémon Magearna using the QR Code.
Visit Pokemon.com starting on December 5, 2016, to find the QR Code that will unlock Magearna in your game. To scan a QR Code in Pokémon Sun or Pokémon Moon, you’ll need to unlock the QR Scanner feature, which will happen after you complete the main story. Don’t worry if you haven’t completed your game by December 5—the QR Code will be live on Pokemon.com until March 5, 2017.
March 5th is plenty of time to finish the story mode even if you have to wait till after Christmas to play the game.