From Bulbapedia, the community-driven Pokémon encyclopedia.

Newmoon Island (Japanese: しんけつじま New Moon Island) is a island in the Sinnoh region, home to the legendary Pokémon Darkrai. To get to the island, one must recieve the Member's Card (Japanese: メンバーズカード) at a Nintendo event. Due to a glitch in the Japanese version of Pokémon Diamond and Pearl, players are able to reach this area without the Member's Card, a problem that Nintendo has rectified in the English-language version of the games. Nintendo has also issued a patch to numerous retailers in Japan.

When encountered, Darkrai is at Level 40.