While everyone in attendance at the Pokemon Go Stadium event was able to catch Mewtwo on the first try, it won't be as easy for the rest of us.
Now, however, the four Legendaries that players have come to know will be making their way back to the game until #August 31. The Exclusive Raid Battle is different from your typical Raid Battle in that you have to be invited to join in an Exclusive Raid Battle. Some players have managed to locate him in the exclusive raid battle and have shared screenshot of his character model in Pokemon GO as well as his CP during the fight. We assume the unused Legendary Raid Pass asset will be used for this.
Pokemon GO has slowly started to add Legendary Pokemon in the game. However, Mewtwo will only be available through Exclusive #Raid Battles. One player who attended the Pokemon GO event in Japan has already caught a maxed out Mewtwo with a flawless move set, likely the first in the world. In a post on the Pokemon Go Live's website, Niantic said that "In the coming weeks, you, too, will have the opportunity to battle and catch Mewtwo with the new Exclusive Raid Battle feature". But you'll need to be a pretty dedicated player to even have a shot of finding one. When the super rare creature arrives in the invite only Battle Raids, Pokemon GO players who have secured an invitation will want to make sure they have a strong roster ready for battle. Basically, a player will get a successful catch if the RNG is within a certain range, which is expanded based on the number of bonuses a player has.