Players of Pokémon Sword and Shield can catch Shellder in Max Raid Battles from May 20th, 2022 until May 22, 2022, at 4:59 p.m. PDT.

Catch Shellder in Max Raid Battles

Crack open your Pokémon Sword and Pokémon Shield game for some Bivalve Pokémon fun, and you might encounter a Shiny Shellder.

The latest Max Raid Battle event in Pokémon Sword and Pokémon Shield is just too exciting to clam up about. Until May 22, 2022, at 4:59 p.m. PDT, Shellder will appear more frequently in Pokémon Dens. Lucky Trainers might even encounter a Shiny Shellder!

For an opportunity to encounter this Pokémon in a Max Raid Battle, you'll need to connect your Nintendo Switch system to the internet through Y-Comm or by selecting Mystery Gift in the X menu, then selecting Get the Wild Area News. After that, whenever you see a pillar of light shining from a Pokémon Den, you can 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.

Source: https://www.pokemon.com/us/pokemon-news/catch-shellder-in-max-raid-battles/