Pokémon Scarlet and Violet will begin a new series of returning 7-star Tera Raid Battles featuring fully evolved powerhouse Pokémon with the Mightiest Mark, starting with Normal Tera Type Dragonite. The first event runs from Sept. 25 at 12 a.m. UTC through Oct. 1 at 11:59 p.m. UTC, with Dragonite appearing at black Tera Raid crystals in Paldea. Each featured Pokémon can be caught only once per save data, so players who previously caught the event Dragonite cannot catch another but can continue battling it for additional rewards. The returning Pokémon will be featured in succession as part of the event series, with players able to team up with up to three other Trainers to take on the powerful Tera Pokémon.
Source: Official Pokémon website