Regirock is the new Raid boss. With Regice and Registeel finished, only one member of this trio of Legendary Pokémon remains. Regirock will be appearing in Raid Battles at Gyms in Pokémon GO until September 20, 2018.
You’ll only have a limited time to add this Pokémon to your Pokédex. Be sure to bring your friends along with you when you challenge Regirock—you may earn some extra Premier Balls thanks to a recent update.
Regirock 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.
Check out the Pokémon.com guide to training Pokémon in Pokémon GO to get your team up to speed, and then read on for some tips specific to eroding Regirock.