The official Pokémon website has announced that from October 29th, 2021 until October 31, 2021, at 4:59 p.m. PDT, players of Pokémon Sword and Shield will find spooky Pokémon like Sableye, Dusknoir, Zoroark, Corviknight, and Thievul more frequently in Max Raid Battles.

Halloween Max Raid Battles Bring Sableye, Dusknoir, Thievul, and More

Scare up some fun in Pokémon Sword and Pokémon Shield’s Pokémon Dens, and you might find Shiny Zoroark.

With Halloween just around the corner, it looks like even the Pokémon in the Galar region's Pokémon Dens are getting into the holiday spirit. Until October 31, 2021, at 4:59 p.m. PDT, you'll find spooky Pokémon like Sableye, Dusknoir, Zoroark, Corviknight, and Thievul more frequently in Pokémon Sword and Pokémon Shield's Max Raid Battles. You might even encounter a Shiny Zoroark!

For an opportunity to encounter these 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/halloween-max-raid-battles-bring-sableye-dusknoir-thievul-and-more/