https://www.gamespot.com/articles/new-pokemon-go-move-discovered-in-games-code/1100-6461278/

Dataminers have discovered a new move in Pokemon Go, which could potentially hint at the star of a future Community Day event. Reportedly couched within the game's recent update are visual assets related to Meteor Mash (via Pokemon Go Hub and Comicbook.com), an attack that isn't currently available in the mobile game.

In the mainline series, Meteor Mash is the signature attack of Metagross, the powerful Steel/Psychic Pokemon first introduced in Pokemon Ruby and Sapphire versions. Its initial form, Beldum, arrived alongside other Hoenn-native Pokemon when Niantic began adding Gen 3 monsters to Go, but Meteor Mash has been absent from the mobile game up to this point.