How to beat Sierra
Sierra is one of Giovanni's easier minions, although that doesn't mean she's easy to defeat. Here, a team of three Pokémon will be super charged, attacking with high level moves that are boosted by the character's extremely high CP. With the right meters, anything is possible. Just keep in mind that after the first Pokémon things get more hit and miss, with Sierra choosing from three potential options. Once set it stays the same, you might want to consider your first fight with her as an exploratory mission. In addition, his team may change with updates. This is up to date as of January 2020, so watch for updates.
Also, a little advice before diving into the counters themselves. Always swap your first character immediately after loading into battle. This causes a delay in incoming attacks, saving you precious seconds to prepare for a charge attack. Charge moves are your most powerful and are the key to victory alongside your own shields. Burn Sierra's shields as quickly as possible so that your attacks land in subsequent battles. Additionally, if your current character is low on health and isn't about to use a charge move, perhaps let them absorb an incoming charge attack to keep a shield for your remaining characters. Now on the counters.
Sierra will always start with Absol, which should set you up for the fights ahead. The solid counters for Absol with the ideal moveset in parentheses are Lucario (Counter and Power-Up Punch), Tyranitar (Smack Down and Crunch or Stone Edge) and Mackogneur (Counter and Cross Chop). Tyranitar is almost always a great choice as he's strong against most enemies. Watch for its repetition in the next two sections. The next step will be either Alakazam, Lokhlass or Cacturne. Here are counters for those.
Alakazam: Tyranocif (Smack Down and Crunch), Darkrai (Snarl and Dark Pulse) and Dimoret (Snarl and Foul Play)
Lokhlass: Mackogneur (Counter et Cross Chop ou Dynamic Punch), Magnézone (Spark et Wild Charge), Dialga (Dragon Breath et Iron Head ou Thunder), Altered Forme Giratina (Shadow Claw et Dragon Claw ou Ancient Power), Tartard (Mud Shot) ou Bubble + Power-Up Punch et Dynamic Punch), Melmetal (Thunder Shock et Rock Slide ou Thunderbolt)
Cacturne: Mackogneur (Counter and Cross Chop), Cizayox (Fury Cutter and X-Scissor), Lucario (Counter and Power-Up Punch), Mammochon (Powder Snow and Avalanche), Coatox (Counter and Dynamic Punch). Cizayox is your best bet if you don't need to use someone else for synergy with the other two fights.
For the final battle, Sierra will use Demolossus, Tengalice, or Gallame, preparing you for what could be an easy finish. Here are the counters.
Hunting dog: Tyranitar (Smack Down and Stone Edge), Mackogneur (Counter and Cross Chop), Kyogre (Waterfall and Surf), Laggron (Mud Shot and Hydro Cannon), Darkrai (Snarl and Focus Blast)
Tengalice: Mackogneur (Counter and Cross Chop), Cizayox (Fury Cutter and X-Scissor), Scarabrute (Fury Cutter and X-Scissor), Braségali (Counter and Blast Burn), Charizard (Fire Spin and Blast Burn), Heatran (Bug Bite and flamethrower)
Gallame: Lugia (Extrasensory and Sky Attack), Gardevoir (Charm and Shadow Ball), Togekiss (Charm and Aerial Ace), Métalosse (Bullet Punch and Meteor Mash), Corboss (Snarl and Sky Attack)
Assemble a strong team of high CP Pokémon, follow the first tip for changing quickly, and focus on fighting the characters she uses and how to beat Sierra in Pokemon GO.
