The official Pokémon website has announced that players of Pokémon Sword and Shield can encounter Grimmsnarl more often in Max Raid Battles.

Encounter Grimmsnarl in Pokémon Sword and Pokémon Shield Max Raid Battles

Gather your courage to take on this hair-raising Dark- and Fairy-type Pokémon, and you might encounter a Shiny one.

Just in case summertime in the Galar region was feeling too bright, Pokémon Sword and Pokémon Shield’s Pokémon Dens are about to get a whole lot grimmer. Until August 21, 2022, at 4:59 p.m. PDT, Grimmsnarl will appear more often in Max Raid Battles—lucky Trainers might even encounter a Shiny one!

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/encounter-grimmsnarl-in-pokemon-sword-and-pokemon-shield-max-raid-battles