The Member Card is a key item only obtainable through a Nintendo Event. The Member Card allows players to travel to Newmoon Island, where a level 50 Darkrai can be obtained. The Member Card will be distributed via the Nintendo Wi-Fi Connection from August 3rd to September 13th to players of Pokémon Platinum.

Players will need to have unlocked the National Dex and the Mystery Gift option in their game in order to receive the Member Card item.

Source: http://www.pokemonplatinum.com/#/pokemon/darkrai/

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