There are a handful of Pokémon trainers in Pokémon Go who hunt often. They come for a small amount of time, always so often. Due to their frequency, trainers must act quickly to make sure they get the ones they want, especially the legendary Pokémon. If you are a coach who wants to get Regice and get its glossy version, you are lucky to know that the glossy version for Regice is around, and should return to the beginning of the discovery season on June 1st.
June 1 raids should have a shiny Regice available to all players. You have a chance to meet one in 20 whenever you complete a raid, which will give you a decent shot of a potential addition. Regice, along with Registeel and Regirock, have had their shiny versions in the game for some time. Given how long they’ve been in the game, you can expect glossy versions of these Pokémon to be available whenever they appear in raids.
Normally Niantic informs the community if the legendary Pokémon does not have a shiny version when it returns to raids. It happened when Genesect got to five-star raids as an option to Burn a Disc. It would be the same for Regice because of her history.
Make sure you try your luck and defeat him in the battle on June 1st. You have until June 17 to add to your collection before it disappears again.