The official Pokémon website has announced that from June 4th, 2021 until June 6th, 2021, lucky trainers in Pokémon Sword and Shield may come across a Gigantamax Venusaur or a Shiny Politoed in Max Raid Battles.

Battle Gigantamax Venusaur and More in Max Raid Battles

You might even encounter a Shiny Politoed during this rainy Pokémon Sword and Pokémon Shield event.

The rainy season has arrived in the Galar region! Until June 6, 2021, at 4:59 p.m. PDT, you'll find all sorts of Pokémon that enjoy the rain in Pokémon Sword and Pokémon Shield's Max Raid Battles. Be on the lookout for a torrent of Pokémon appearing in Pokémon Dens, including Venusaur, Politoed, Croagunk, and Seismitoad. Lucky Trainers may even come across a Gigantamax Venusaur or a Shiny Politoed.

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. Usually, there'll be an extremely small possibility a Gigantamax Pokémon will appear instead of a Dynamax Pokémon, but during an event, certain Gigantamax Pokémon are more likely to appear. This event does not affect the Pokémon encountered within Dynamax Adventures.

Be sure to read our Pokémon Sword and Pokémon Shield Max Raid Battle Tips article for advice on how to topple these opponents. Don't wait, though—you don't want to miss out on the chance to add these Pokémon to your team!

Source: https://www.pokemon.com/us/pokemon-news/battle-gigantamax-venusaur-and-more-in-max-raid-battles/