Arceus coming to Pokémon Brilliant Diamond and Shining Pearl in new update

polygon.com:

Two powerful legendary Pokémon, Arceus and Darkrai, will make their way to Pokémon Brilliant Diamond and Shining Pearl for the first time. Each Pokémon has its own set of circumstances players need to fulfill to unlock them, but Arceus will be available to those who have Pokémon Legends: Arceussave files starting March 16.

To unlock Arceus, you’ll need to have save data from a completely different game, Pokémon Legends: Arceus, and have the 1.3.0 version of Brilliant Diamond and Shining Pearl downloaded. Players will be able to receive the Azure Flute item and meet Arceus at Spear Pillar if they’ve beaten the Elite Four and gotten the National Pokédex.

Getting Darkrai will work a little differently. The Pitch-Black Pokémon will come as part of a time-limited mystery gift event that will run from April 1 to April 30. That event will give you the Member Card item to go see it. Like Arceus, you’ll need to make sure you’re at the right point in the game to meet it. To see Darkrai, you’ll need to have entered the Hall of Fame, gotten the National Pokédex, and completed the in-game event for Cresselia.

All three games — Pokémon Brilliant Diamond, Pokémon Shining Pearl, and Pokémon Legends: Arceus — are available on the Nintendo Switch.