If you’re looking to get more Max Raid Battles happening Pokémon Sword and Shield, you’ll need to acquire a Wishing Piece. It’s a useful item you can get from the Watts vendor, which costs 3,000 Watts to purchase. The most iconic location for the Watts vendor is at the entrance to Motostoke, at the bottom of the stairs in the black-and-white outfit. When you get it, you can find it in the “Other Items” section of your bag.
You can use the Wishing Piece in the Wild Area of the Galar region. You need to approach an already vacated den, which should look grey. You cannot use it on glowing dens, or if it has a bright red light coming out from the middle.
When you locate a vacated den, typically, you cannot interact with it further. But if you have a Wishing Piece, you have the option to lure a Dynamax Pokémon to this location. When you throw your Wishing Piece in, you receive a notification to save your game. Now, you should see a distinct, dark light shooting out from the den. You can approach it and treat it like every other battle with a Dynamax Pokémon, where you can choose to invite other players or not.
Usually, when you approach a den with a Dynamax Pokémon in it, you receive Watts from the energy. However, because you lured the Pokémon there, you won’t get any Watts when you approach the den. Regardless, you have the opportunity to fight a Dynamax Pokémon and receive some great experience points for finishing the encounter.
Using the Wishing Piece consumes it, and you’ll have to get more to use in the future.