Starting Dec. 4, you can catch Gigantamax Snorlax in Pokémon Sword and Shield. Gigantamax Snorlax will be on the Max Raid Battles rare encounters schedule, giving you a chance to catch him whenever you take part in a Max Raid Battle. These potential encounters will last until early January, so you have about a month to find him.
Max Raid Battles involve a team of Trainers taking on a mighty Pokémon. You can take part in them as soon as you arrive in the Wild Area, but they are challenging at that stage in the game. Look for glowing red rock formations with a beam of light coming from them to join a Max Raid Battle. While it is possible to take part in these Battles with AI teammates if you are offline, you will only be able to get Gigantamax Snorlax by taking part in online battles.
When you are taking on Gigantamax Snorlax, you need to watch out for his special G-Max Replenish move. This powerful move deals damage and restores berries that the Snorlax and his allies have eaten during the battle. When you beat the Snorlax in a Max Raid Battle, you have the opportunity to catch it.
There is no guarantee that any Max Raid Battle you take part in will feature a Gigantamax Snorlax, there will be an increased chance of encountering it over other types of Pokémon during the event. Some methods allow you to get Gigantamax Meowth, Eevee, and Pikachu under particular conditions. Meowth is available as an early purchase bonus, while Eevee and Pikachu are only available to people with a relevant Let’s Go save file on their Switch.