For more information on the Pokemon Sword and Shield Max Raid Battle event, see the following link.
Pokemon Sword and Shield are now on hold for the second Max Raid Battle event, which featured Shellder and Shiny Shellder until May 22 at 4:59 p.m. PT.
For an opportunity to encounter these Pokemon in a Max Raid Battle, you must connect your Nintendo Switch system to the internet by selecting Y-Comm or by selectingMystery Giftin the X menu, then selectingGet the Wild Area News. After that, whenever you see a pillar of light shining from a Pokemon Den, you may walk up to the Pokemon Den and interact with it to start a Max Raid Battle with a Dynamax Pokemon. This event does not affect the Pokemon encountered within Dynamax Adventures.