Team GO Rocket won't stop causing mayhem with Shadow Pokémon in Pokémon GO. Look for new Shadow Pokémon, like Sandshrew, Sandslash, Bellsprout, Weepinbell, Magnemite, Magneton, Porygon, Wobbuffet, and Chimchar, to begin appearing in Team GO Rocket's discolored PokéStops.
It's up to you to drive those Team GO Rocket Grunts out of the PokéStops with a battle. You'll then have the chance to catch one of their abandoned Shadow Pokémon and, if you choose to, purify it. If you enjoy taking your Pokémon out on Pokémon GO Community Days, there's a good reason to purify them—if you have a Pokémon that's eligible to learn a new move during one of the monthly Community Days, it will be unable to do so if it's a Shadow Pokémon. Purified Pokémon, however, can learn these special event-exclusive moves.
It's up to you to save these Pokémon, Trainers. Good luck!