Start/End Dates	2012-09-15 through 2012-10-28
Country	Japan

Details

Japanese players of Pokémon Black 2 and White 2 who visited a Pokémon Center from September 15th until October 28th got the chance to obtain a random Pokémon out of several that were deemed to be the most powerful Pokémon in Single Battles. These five Pokémon were selected based on the Pokémon that are used more frequently in Single Battles on the Pokémon Global Link.

Once the player received their Pokémon, players could show a Pokémon Center staff member which Pokémon they got and the staff member would give the player a "post card-shaped battle guide sheet" with various training tips on that particular Pokémon.


Source: http://www.pokemon.co.jp/info/2012/08/120817_p01.html
Scan source: http://d.hatena.ne.jp/asami-1120/