Whether you’re playing a handheld Pokémon RPG or the Trading Card Game, Nintendo is giving players access to a new, powerful Pokémon, Darkrai. A new TCG expansion, Black & White – Dark Explorers, is now available in retail stores nationwide, including normal and Ultra Darkrai-EX cards. Additionally, players of Pokemon Black & White can get their hands on a level 50 Darkrai through Nintendo Wi-Fi Connection if they access it before June 10. More information can be found at this website, which also contains a “special showing” of the newest Pokémon feature film, Pokémon: The Rise of Darkrai.
If I could find my copy of Pokémon Black, I’d probably be doing this.

if i used an older Pokemon game such as Pokemon Platinum or Pokemon Soul Silver or go a little farther back to Pokemon Diamond would this giveaway still work or do i have to use Pokemon Black or Pokemon White? Also do i have to go to a store or can i do it from home?
The press release stated that it was available to players of Pokémon Black & White, so I assume it needs to be that game. It also specified Nintendo Wi-Fi Connection, so you should be able to get it from home.