Experience new encounters on the night of the new moon! New Moon Day will begin near the end of May 2025! Details for other events will release at a later date, so keep your eyes out for more soon!

YouTube Clip - New Moon Day Event | Pokémon Sleep

Source: https://www.youtube.com/watch?v=C6EhYf9b1Vo

New Moon Day

The darkness of a new moon lets new encounters shine! Beginning around the end of May 2025, we’ll hold an event themed around the new moon—New Moon Day! During this event, Pokémon won’t get full easily during snack time. You may even meet the Mythical Pokémon Darkrai! More details about the event are coming in a later update. We hope you’re looking forward to this!

Source: https://www.pokemonsleep.net/en/news/323630323035333235363632303237373737/