From June 21st, 2018 until July 19th, 2018, players of Pokémon GO will be able to battle Regice in Raid Battles. Regirock and Registeel will be available later in the summer.

The Legendary Pokémon Regice Is Ready for Bone-Chilling Raid Battles!

Trainers, Pokémon’s legendary year continues with three Legendary Pokémon originally discovered in the Hoenn region harnessing their power to take over Raid Battles in Pokémon GO, starting with Regice on June 21!

Regice, the Iceberg Pokémon, has awakened from its slumber and will be the first to appear in Raid Battles across the world until July 19. This Ice-type Legendary Pokémon has a strong defense, but is weak to Fire-, Fighting-, Rock-, and Steel-type attacks.

The presence of this defensive powerhouse kicks off a summer of earth-shattering events, as Regirock and Registeel will also roar into Gyms worldwide!

Don’t miss this chance to catch this Legendary Pokémon before it returns to another long slumber! Stay safe, and happy exploring!

Source: https://pokemongo.nianticlabs.com/en/post/legendary-regice/