The Pokémon Go Fest 2020 event will operate differently from previous years, as it is a virtual event that anyone in the world can participate in, rather than in a physical location. This is happening to help prevent the spread of COVID-19, ensuring everyone stays safe inside their homes. Because the event is virtual, everyone in the world can attend it during the weekend of July 25 and 26. In the last few weeks leading up to the event, members of Team Rocket stirred up trouble and developed a new ball system. to capture Pokémon and battle trainers. Team Rocket will no doubt be present at the Pokémon Go Fest 2020 event. Dataminers have discovered that Giovanni will show up with a Shadow Mewtwo that you could probably attempt to capture.
The Pokeminers shared their findings on their twitter and Reddit page, where they first showed Shadow Mewtwo the assets. They have now confirmed that the Shadow Mewtwo will be part of the Pokémon Go Event Fest 2020 where trainers will have to fight it. While we don't know of his first two Pokémon, we do know that he will have a Shadow Mewtwo, which can give Trainers enough advantage to knock him down during the event.
Mewtwo is purely a Psychic-type Pokémon, which makes it weak to Bug, Ghost, and Dark-type attacks. You mainly want to focus on using Pokémon, such as Chandelure, Gengar, Darkrai, Tyranitar, Absol, Pinsir, or another Mewtwo who knows the Shadow Ball. Mewtwo is a strong foe, so it's best to try and find a Pokémon that is resistant to psychic-type attacks. If Giovanni uses two Pokémon before Shadow Mewtwo, try forcing him to use his shields on those two before reaching Mewtwo to make it harder to block any powerful attacks against him.
We'll update this guide closer to the event when we learn details about Giovanni's makeup if he has any additional Pokémon beyond Shadow Mewtwo. Hopefully it comes with a range similar to the one it used in July 2020.