You can now get Arceus in Pokémon Brilliant Diamond and Shining Pearl, Darkrai next month

gamepur.com:

Arceus is the latest Mythical Pokémon that trainers will be able to add to their Pokédex starting today in Pokémon Brilliant Diamond and Shining Pearl. Announced on the Pokémon Twitter account, players will be able to capture Arceus at the Spear Pillar after meeting a few conditions. Darkrai will also come to the game between April 1 and May 1.

To capture Arceus, players must have a save file from Pokémon Legends: Arceus on their Switch that has all the main missions from the game completed. You also must have beaten the Pokemon League and received the National Pokédex in Brilliant Diamond or Shining Pearl to receive the Azure Flute, which you will find in your bedroom back at home. Once then, you will be able to travel to the Spear Pillar to take on Pokémon’s version of God. Make sure that you have the latest update of Brilliant Diamond and Shining Pearl (version 1.3.0) before you try to get Arceus.

To obtain Darkrai, similarly to Arceus, you must have gotten into the Hall of Fame after completing the Pokemon league and obtaining the National Pokédex. By going to the Mystery Gift feature you will receive the Member Card item. After that, you can travel to Newmoon Island where you can fight Darkrai.

With Arceus and Darkrai coming to Brilliant Diamond and Shining Pearl, they mark the last two Mythical Pokémon of the Sinnoh region that have made it to the game.