Here's how it works: Come April 4, anyone who walks into a GAME retail location with a copy of Pokemon X or Y will walk away with a rare Pokemon. Players who own Pokemon X will receive the fiery Magmar, while those who own Pokemon Y will add Electabuzz to their Pokedex. Additionally, both Pokemon come equipped with the items necessary to evolve into their final forms. Both Magmar and Electabuzz will be distributed in the form of a code printed on a GAME receipt, though the retailer claims that no purchase is necessary to receive a free 'mon.
Not wanting fans of the Pokemon trading card game to feel left out, GAME will also be handing out free sample card packs, each of which includes a "special foil Pikachu card." Like the virtual Pokemon, there's no purchase necessary for this piece of swag, though GAME notes that these sample packs will be handed out on a first come, first served basis. Once supplies are gone, you'll have to find some other way to catch 'em all.
Edit: Originally this article claimed that the items attached to Magmar and Electabuzz would allow the Pokemon to Mega Evolve, when in fact neither of these creatures have the ability to Mega Evolve.