Mew, one of the original legendary Pokemon from the first 151, is going to be available for download on Pokemon X, Y, Omega Ruby, and Alpha Sapphire, if you sign up for the Trainer Club account on the official website.
If you sign up before June 1st, you can get the newsletter which provides the code to download it. According to the official website, this code will have to be redeemed by August 31st.
With the Trainer Club account, you can play the Trading Card Game online, use Global Link, and collect Trainer Tokens and Stamps.
Once redeemed and uploaded to the cloud, Mew will be available to play in Sun and Moon, which releases on November 18th, 2016.
By the way, if you haven’t played Pokken Tournament yet, check out our review of the game here.
Good luck on your continuing adventures to catch ’em all, everyone!
Source: Pokémon News
