Roselia, the thorn Pokémon from Hoenn, can be found in the wild in Pokémon Go. Yes, Roselia can be shiny in Pokémon Go!
Roserade is actually a really good grass- and poison-type attacker, so it’s worth grabbing a powerful one if you can. If you already have a shiny Roselia (or any of its family members), it’s likely from a previous Roselia Community Day event that happened in February 2021.
What is the shiny rate for Roselia in Pokémon Go?
As per old research by the now-defunct website The Silph Road (via Wayback Machine), the shiny rate for Pokémon on a regular day is approximately one in 500. Roselia is not a confirmed Pokémon that gets a “permaboost” (meaning that it’s a rare spawn and thus gets a boosted shiny rate).
What can I do to attract more shiny Pokémon?
Not much, unfortunately. It appears to be random chance. Shiny Pokémon catch rates are set by developer Niantic, and they are typically only boosted during special events like Community Days or Safari Zones, or in Legendary Raids. There are no consumable items that boost shiny Pokémon rates.