The Hisui region exists on the land that many players know as Sinnoh, though long before people settled into the towns and cities that players of Pokémon Diamond, Pearl, Platinum, Brilliant Diamond, and Shining Pearl are familiar with. As such, many Pokémon native to the Sinnoh region can be found in Hisui, including a handful of Legendary and Mythical Pokémon.
One of these Pokémon is the Pitch Black Pokémon, Darkrai. This Pokémon is said to put its enemies to sleep and inflict terrible, never-ending nightmares that torment them for life. Darkrai could originally only be found through an event in Pokémon Platinum that awarded players with the Member Card, giving them access to a locked house in Canalave City that would bring them to Newmoon Island, home to the Pitch Black Pokémon.
In Pokémon Legends: Arceus, Darkrai is once more locked behind a specific prerequisite. If players have save data for Pokémon Brilliant Diamond or Shining Pearl in their Nintendo Switch system, they will be awarded a special research quest to hunt down Darkrai after they complete the game’s main story. Request 93, known as “The Darksome Nightmare,” can be accepted via Professor Laventon’s request board in the Galactic Building.
Upon encountering Darkrai, players will first have to escape its quick, aggressive attacks aimed at them. They’ll then be tasked with battling and capturing the Pitch Black Pokémon, giving them the chance to add this powerful Mythical Pokémon to their teams.
Outside of this event, there is currently no other way to obtain Darkrai in Legends: Arceus. Future events through the game’s Mystery Gift feature may allow other players to experience this mission without having access to Brilliant Diamond or Shining Pearl, though that possibility is currently unconfirmed.