The other two mythical Pokemon of Pokemon Diamond and Pearl will be coming in soon, though one will require some additional blessings.

Following the distribution of Shaymin on February 27, Darkrai and Arceus will be available following a software update (v1.3) for Pokemon Brilliant Diamond and Shining Pearl. The requirements are:

• Darkrai requires a Mystery Gift for the "Member's Card" that will be distributed beginning on April 1. Once obtained, the card can be used to enter a locked house in Canalave City which leads to Newmoon Island for a fixed encounter. This requires beating the Elite 4 and obtaining the National Pokedex.
• If a save file for Pokemon Legends Arceus that has completed all of the postgame events is on the same Switch system following the update, it will be possible to obtain the Azure Flute item in the player's room. Provided the same progress requirements (beat Elite 4, obtain National Pokedex) are obtained in game, the Flute can be taken to the top of the Spear Pillar to fight Arceus.

Both items along with the Oak's Letter were in Pokemon Diamond / Pearl / Platinum, though the Azure Flute was never distributed previously with the only Arceus coming from a Mystery Gift event. Arceus by way of this event come at level 80, the second highest encounter of a static wild Pokemon in series history.