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Dark Void is the signature move of Darkrai. In the games Pokemon Diamond, Pearl, and Platinum (where it is seen), it sends the foe into a dark vortex and puts it to sleep. It has 80% Accuracy, 10 PP, and falls under the Status category. In a Double Battle both opponents fall asleep. This move is Dark type.
anime
In the anime, Darkrai forms spheres from his hands and throws them in all directions, causing them to sleep and have nightmares. Like the games, the targets are put to sleep, and Darkrai's Bad Dreams ability comes into play, causing damage to the opponent.