A new update to Pokémon Go has Team Rocket grunts popping up at Pokéstops to battle trainers.

Team Rocket grunts will battle you at a Pokéstop, similarly to how you can battle team leaders. If you win, they’ll run off and leave their Shadow Pokémon behind. From there, you can catch the Pokémon with Premier Balls, as you do in a raid. These Shadow Pokémon need to be purified on their information screens using their respective candy and dust. The button to purify sits right above the button to power them up.

Shadow Pokémon have a dark aura around them. Their CP is heavily reduced when shadowed. Shadow Pokémon also learn Return, a normal-type attack, when purified, which makes them well worth the trouble. Some players are reporting right now that purified Pokémon also appear to require less candy to evolve and less dust to power up.

The mechanics for Shadow Pokémon seem to be inspired by Pokémon Colosseum and Pokémon XD: Gale of Darkness for the GameCube. Both the games focused on taking Shadow Pokémon away from trainers who received them from a suspicious organization. In those games, you would purify the Pokémon through battling with them or using a special chamber. We’ll keep tabs on the update to see if any more new features or mechanics are hidden inside.