This is a Wild Area event held by Sword and Shield. This event is an event tie in to M23: Secrets of the Jungle.
It features Pokémon that appears in the movie, and also give players a chance to encounter a shiny Cramorant! (2% guaranteed shiny at 5 star tier)
Besides that, there are also specific rewards for the amount of times Max Raid Battles against Cramorant were won:
500,000 battles won: players receive a Flame Orb, Toxic Orb, and Light Ball
1,000,000 battles won: players receive a Gold Bottle Cap, 3 Bottle Caps, and 3 Pearl Strings.
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 contains 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.
(details source: https://www.pokemon.co.jp/info/2021/01/210129_gm01.html)