For a criminal organization, Team Rocket is very polite about keeping to a schedule. So polite, in fact, that they give Pokémon GO players a good idea of what to expect in battle. Every month the villains change their lead Pokémon, and players share the changes to help each other emerge victorious. The February switch happened (almost) on schedule, and players are already reporting what new Pokémon Cliff, Arlo, and Sierra have added to their lineups.
Thanks to several reports on Pokémon GO subreddit The Silph Road, we know that Arlo now leads with Mawile, Cliff leads with Pinsir, and Sierra leads with Beldum. We also know that there were some issues with the monthly team switch as of February 3. Make sure you update your game to the latest version if you want to take on these new Shadow Pokémon.
Beating Arlo
There seems to be a common theme to February's Rocket Leader changes – Niantic knows we're steamrolling the baddies with strong Fighting-types and they're putting a stop to it. Every one of the new lead Pokémon has some resistance to Fighting-type attacks. Arlo's new leader is the Fairy/Steel Mawile.
Fire-types have always been strong against Arlo since he favors the Steel type. Burning Mawile continues to be a solid strategy. However, Arlo can still pack a Charizard and a Salamence, both of which resist fire. So be sure to bring a Rock-type along to deal with them. As always, Tyranitar is a strong pick. Just don't lead with Tyranitar against Mawile.
Beating Sierra
Sierra now leads with Beldum. This should be the weakest of the trio since it's in its unevolved state. As for her other Pokémon, she's been reported having a Sharpedo and a Houndoom.
Sierra loves her Dark-types, which made her the easiest Team Rocket Leader to destroy with a good Machamp. This is still mostly the case, but you probably don't want to lead with Machamp against the Psychic-type Beldum. Instead, bring out good ol' Tyranitar. Just be sure to switch out Tyranitar as soon as Beldum goes down so it doesn't face Sharpedo's Water-type wrath.
Beating Cliff
Cliff now straight up counters your Fighting-type lead by starting with a Pinsir. The Bug-type also counters Dark-types, so Tyranitar might have some trouble as well.
Cliff can also have Electivire and Tyranitar. There's not much of a common theme here so you'll have to pack an equally varied team. A Rock-type is a great pick against Pinsir. Perhaps upcoming Community Day star Rhyhorn will be of assistance once it's evolved. A Ground-type could do some damage to Electivire and Tyranitar. A Swampert should be a good closer due to its decent bulk and Water/Ground combination.
Good luck! And don't forget, every one of these new Shadow Pokémon can be shiny!