It appears the leaks and rumors concerning an armored form of Mewtwo appearing in the Pokémon games were true. This is demonstrated by a video on the official YouTube channel for Pokémon that has revealed Armored Mewtwo is coming to Pokémon Go this month.
The version of Armored Mewtwo is the same as the one that has appeared in the trailers for the upcoming Pokémon: Mewtwo Strikes Back - Evolution movie. In the original version of the movie, Mewtwo is shown wearing a suit of robotic armor that is given to him by Giovanni of Team Rocket. The armor used by Mewtwo in the trailers for Pokémon: Mewtwo Strikes Back - Evolution is different and it's possible that he dons it himself during a later stage of the movie.
The new trailer for Pokémon Go has revealed that the version of Armored Mewtwo from the upcoming Pokémon movie will be appearing in Raid battles starting from July 10 and will last until the end of the month.
The reveal of an armored version of Mewtwo in Pokémon Go was leaked back in April through a datamine of the game. The fans had expected it to be related to the rumors of a new mechanic in Pokémon Sword & Shield known as Armored Evolutions, which supposedly allow certain Pokémon to take on new forms based on specific held-items. Pokémon Sword & Shield are due to be released in a few months and there has yet to be any official announcement made regarding Armored Evolutions, so it's possible that the rumors were never true.
The trailer for Armored Mewtwo in Pokémon Go ends with the player catching Armored Mewtwo, which suggests that it could be traded to different Pokémon games in the future. It's possible that Armored Mewtwo is classed as a unique form for Mewtwo and that it won't be part of a new kind of evolution. The success of Pokémon Go prompted Game Freak to introduce Meltan (and its evolution) in the game, rather than in an official mainline entry in the series, so there is a precedent for new concepts in the Pokémon series debuting in Pokémon Go. The fans won't have long to wait until they discover whether Armored Evolutions are real or not, as Pokémon Sword & Shield are due to be released in November.
Armored Mewtwo will appear in Pokémon Go from July 10 to July 31.