The official Pokémon website has announced that Galarian Rapidash, Galarian Darumaka, Mandibuzz, Sirfetch’d, and more version-exclusive Pokémon might appear in Max Raid Battles from Wednesday, March 18th, 2020, at 5:00 p.m. PDT until Wednesday, March 25th, 2020, at 4:59 p.m. PDT in Pokémon Sword and Pokémon Shield.

Galarian Rapidash, Galarian Darumaka, Mandibuzz, Sirfetch’d, and more version-exclusive Pokémon might appear in Max Raid Battles

Take this opportunity to catch Pokémon that don’t normally appear in the wild in your game version, as well as other Pokémon that may be hard to find.

From Wednesday, March 18, 2020, at 5:00 p.m. PDT until Wednesday, March 25, 2020, at 4:59 p.m. PDT, Pokémon Sword and Pokémon Shield players may encounter some Pokémon that may be hard to find in Max Raid Battles. All players may encounter Dynamax Escavalier, Accelgor, and Pincurchin more frequently in Max Raid Battles. Plus, Pokémon Sword players might encounter Dynamax Galarian Rapidash, Galarian Corsola, Mandibuzz, Oranguru, and female Indeedee. While Pokémon Shield players might encounter Dynamax Galarian Darumaka, Braviary, Passimian, Sirfetch'd, and male Indeedee instead. These Pokémon normally do not appear in these game versions, so it's a great opportunity to work toward completing your Galar Pokédex.

To challenge these Pokémon in a Max Raid Battle, 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, you can walk up to the Pokémon Den and interact with it to start a Max Raid Battle with a Dynamax Pokémon. In extremely rare cases, a Gigantamax Pokémon can appear instead of a Dynamax Pokémon.

Source: https://www.pokemon.com/us/pokemon-news/galarian-rapidash-galarian-darumaka-mandibuzz-sirfetchd-and-more-version-exclusive-pokemon-might-appear-in-max-raid-battles/