Start/End Dates	2011-09-26 through 2011-10-31
Country	Japan

Details

Junichi Masuda appeared on Pokémon Smash 50 to announce details about the Mewtwo event revealed by Shoko-tan on Pokémon Smash 49. The event distribution took place from September 26th, 2011 until October 31st, 2011 on the Japanese Nintendo Wi-Fi Connection for players of the Japanese versions of Pocket Monsters Black & White. Mewtwo's fourth move was revealed by Shoko-tan on Pokémon Smash #51 which aired on September 25th, 2011. The fourth move is: Electro Ball, a move Mewtwo normally cannot learn.


Source: http://www.pokemon.co.jp/ex/mewtwo/feature/index.html#feat02