Pokémon Go Is Flipping the Big Shiny Switch

Let me quote what they said in the season page of the next on, Memory’s in motion

“Any evolved Pokémon in the wild can be Shiny if it has already had its Shiny debut in Pokémon GO!In addition, Trainers will have an increased chance of encountering Shiny Pokémon from Raid Battles and hatching them from Eggs compared to wild encounters.Any Pokémon rescued from Team GO Rocket that has made its Shiny debut can also be Shiny—if you’re lucky! Trainers will have an increased chance of rescuing Shiny Pokémon from Team GO Rocket leaders and Giovanni compared to Grunts.”