Mewtwo

Mewtwo is a Psychic-type Legendary Pokémon from the Kanto region. It doesn't evolve from or into any other Pokémon. It is only available for capture when defeated as a Raid Boss during an EX Raid Battle.

Trivia

 * Niantic has announced it will only be available in future exclusive events, such as EX Raids.
 * On August, 2017, one day before the Pokémon GO Stadium event, a shiny variant was added to the game files, along with stat changes. Mewtwo was confirmed as a Raid Boss the following day.
 * Trainers who defeated a Mewtwo Raid Boss at Pokémon GO Stadium received over 50 Premier Balls and an increased capture rate.
 * As a Raid Boss, Mewtwo's CP was 49,430.
 * Mewtwo's maximum capture CP in Bonus Challenge was 2,275.
 * CP of Mewtwo with perfect IVs at level 20 is 2,275 and at level 40 is 3,982.
 * That makes it the highest maximum CP Pokémon from Kanto region and one of the highest max CP Pokémon in game.
 * Mewtwo has the highest Attack statistic in the game.