The official Pokémon website has announced that to celebrate World Penguin Day on April 25th, 2021, Pokémon Sword and Shield Max Raid battles will feature Eiscue. The event will be active from April 23rd, 2021 until April 25th, 2021.

Celebrate World Penguin Day with Max Raid Battles Featuring Eiscue

Through April 25, the Penguin Pokémon Eiscue will be appearing more frequently in Max Raid Battles.

World Penguin Day is April 25, and there's no better way to celebrate the adorable flightless bird in Pokémon Sword and Pokémon Shield than with Max Raid battles featuring Eiscue, the Penguin Pokémon! Eiscue will be appearing more frequently in Max Raid Battles through April 25 at 4:59 p.m. PDT. Lucky Trainers might even encounter a Shiny one, which has a pastel pink ice cube on its head.

To encounter Eiscue in Max Raid Battles, you'll need to connect your Nintendo Switch system to the internet. Then, whenever you see a pillar of light shining from a Pokémon Den in the Wild Area or elsewhere, walk up to the Pokémon Den and interact with it to start a Max Raid Battle with a Dynamax Pokémon. This event does not affect the Pokémon encountered within Dynamax Adventures.

Happy World Penguin Day!

Source: https://www.pokemon.com/us/pokemon-news/celebrate-world-penguin-day-with-max-raid-battles-featuring-eiscue/