Regice was initially made available around the world in Pokémon GO Raid Battles until July 19. The Legendary Ice-type Pokémon was replaced by Registeel until August 16 at 20:00 UTC, which means the third of the trio – Regirock – is now available worldwide until September 20 at 20:00 UTC.
These Legendary Pokémon can be caught only with the Premier Balls you earn from defeating it, so you’ll need your Pokémon to perform well in battle to maximize your chances. You can participate in Raid Battles even if you’re not high-level or if your Pokémon aren’t the strongest, but you’ll have an easier time if you prepare.
Trainers, don’t forget to catch Regirock before it repairs itself and travels away on September 20! pic.twitter.com/trE6QFsrKa
— Pokémon GO (@PokemonGoApp) September 9, 2018