This is a Wild Area event held by Sword and Shield. All the event slots are held by Pokémon that can Gigantamax.
This marks the first time the Gigantamax variants of Gengar, Lapras, and Appletun can be encountered on Pokémon Sword (without being hosted by a player that has Pokémon Shield).
This also marks the first time the Gigantamax variants of Machamp, Coalossal, and Flappe can be encountered on Pokémon Shield (without being hosted by a player that has Pokémon Sword).
This Wild Area event also sees the return of Gigantamax Snorlax and Gigantamax Toxtricity, which normally cannot be found in the base games without Wild Area events.
To import these files into your save, use PKHeX's block importing function. Our tutorial should guide you through it.
Our first post of this page would contain some data relevant to the importing stage.
There's info and some common questions regarding Wild Area Events here.
To see other Wild Area Events, here.