Players of Pokémon Sword and Shield can encounter Milcery in Max Raid Battles from February 11th, 2021 until February 14th, 2021.

Face Milcery and Earn Sweets in Max Raid Battles

Use the Sweets you earn during this Pokémon Sword and Pokémon Shield Valentine’s Day event to evolve a Milcery into an Alcremie that can Gigantamax.

Pokémon Sword and Pokémon Shield players will have a particularly sweet Valentine's Day this year. Until February 14, 2021, at 3:59 p.m. PST, you'll be more like to encounter Milcery in Max Raid Battles. These Max Raid Battles will reward you with all sorts of Sweets—including Star Sweets and Ribbon Sweets, which are only available during special events. When Sweets are held by a Milcery, they allow the little Cream Pokémon to evolve into different forms of Alcremie.

Any Alcremie you evolve from the Milcery you catch during this event will be capable of Gigantamaxing, so you'll want to take advantage of all the Sweets you earn. Be sure to keep your eyes open as you take on Max Raid Battles, too, because you'll have a small chance to encounter a Shiny Milcery during this Valentine's Day event!

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/face-milcery-and-earn-sweets-in-max-raid-battles/