Soon, a new downloadable Pokemon game will be released in Japan—free of charge. Called Thief and 1,000 Pokemon, the 3DS game has players amass an army of Pocket Monsters via StreetPass.
Those Pokemon are then used in battle. The more you have, the better your chances are for winning.
The game will be available in the Japanese Nintendo eShop free of charge from June 6 to September 30. No word yet about a Western release.