A new Pokémon Go update has brought Team Rocket to your neighbourhood, alongside two new Pokémon types: Shadow and Purified.
Some PokéStops are now blackened and guarded by a Team Rocket grunt who players can fight. Win, and they’ll leave behind their Shadow Pokémon. These sad creatures are a corrupted type, made after ordinary Pokémon are forced into doing bad things that eventually close off their souls.
Thankfully, once you’ve beaten three of a grunt’s Pokémon in PVE combat, you can capture their Shadow Pokémon. To do this you’ll need to use a Premier Ball (like in a raid) and “purify” the creature back to normality afterwards using Stardust or Candy. You could also keep them in their Shadow state, if you’re the sort of person that pulls legs off flies.
Source: IGN.com Team Rocket Join Pokémon Go and Introduce Two New Types