With the new 1.3.0 update of "Pokemon Brilliant Diamond" and "Pokemon Shining Pearl," you can now add the nightmarish fury of Darkrai and the divine power of Arceus to your team roster. Although you don't need to complete every single task in the game, you still need to reach the end of the main plot to unlock the pair of Pokemon that are classified as "legendary."

For Darkrai, you need to unlock the National Pokedex by seeing all 150 Pokemon and get into the Hall of Fame by beating the Elite Four and becoming the new Pokemon Champion. Then you have to get ahold of the Member Card, which is available via the Mystery Gift menu option "between the new moons" in our world outside the game — meaning that in 2022, you've got a window of opportunity between April 1 and April 30.

Then return to Canalave City, visit the house with the blue roof to the north of the Pokemon Center, and speak to the NPC waiting inside. Go to bed following the prompts, and in your dream, you'll find yourself on Newmoon Island, where you can wander around until you find Darkrai, but be prepared for a tough fight against a legendary Dark-type Pokemon who's weak to Fairy, Bug, and Fighting attacks.

Finding Arceus also requires you, the Pokemon Trainer, to be part of the Hall of Fame by beating the Elite Four and unlocking the National Pokedex. However, unlike in the case of Darkrai, to unlock Arceus, your Nintendo Switch needs to have the game "Pokemon Legends: Arceus" loaded to a point where you have game save data in your device's memory, though you don't need to complete the video game.

If you meet all those prerequisites, go back to your room from the very start of your game, find the Azure Flute item, visit the Spear Pillar at the top of Mount Coronet, and Arceus will be waiting. Although Arceus is weak to Fighting moves, you should still be prepared for a tough fight since it is a Pokemon god that participated in the creation of the entire world.