All five of the Team Star Bases work in a similar way, so here’s a bit of an explanation of what to expect when taking them on.
First of all, you’ll usually have to challenge someone near the gate of a Team Star Base before you’ll gain entry, so prepare yourself for a Trainer Battle. This usually gives you an idea of what sort of Pokémon to expect within.
The next phase is the Star Barrage phase, where the first three Pokémon in your party will need to auto-battle against a bunch of the Team Star Grunt’s Pokémon, all at once. Before taking on the Team Star Base (but after fighting the Trainer at the gate), make sure you position the three Pokémon you think will do best against the respective type at the front of your party! These will be the only three Pokémon you’ll be able to send out during this phase.
You’ll have 10 minutes to defeat a total of 30 Pokémon using the auto-battle mode—the Let’s Go! mode. Unlike normal auto-battle, where you can only send out your lead Pokémon, during the Star Barrage, you can send out three Pokémon at a time, although they get sent out one at a time by pressing the R button and, while one of them is sent out, it will then choose the next one in your party of three to send out afterwards.
For instance, if you have an Azumarill, a Klawf, and a Krokorok while taking on the Fire-type Team Star Base, you’ll first send out the Azumarill by pressing the R button and it will attack nearby Pokémon—make sure you face the Pokémon you want to use Azumarill (or whatever your Pokémon is) against and target them first so it will actually fight them! Then, while Azumarill is fighting, you can keep moving forward and find another batch of Pokémon to fight and press R to send out the next in line, Klawf.
Keep moving forward, sending out your Pokémon to fight against the Star Barrage, and eventually you’ll take down the 30 Pokémon necessary. If your Pokémon get weakened, they won’t be able to fight, so you can heal your Pokémon at any vending machine, although it will take a little bit of time to do this.
As far as strategies go, chances are, if you have a balanced team, you’re not going to have coverage with all three of your Pokémon. You might have one or maybe two that are super effective, but another might not be, and that’s fine, just try to have the less effective ones sent out against Pokémon that are weaker or have a secondary type that’s weak to one of their types or move types, for instance using a Fighting-type Pokémon in the Fire-type Star Barrage and using it to fight against Houndour, which is part-Dark-type.
The Boss and the Starmobile
After you’ve cleared the Star Barrage, the Team Star Boss will appear in a flashy entrance and will formally accept your challenge. Whichever Pokémon was in the front of your party at the start of the Star Barrage is what you’ll send out against them, so keep that in mind.
They’ll use a few Pokémon on their team, usually with a strategy that helps them counter potential counters to their weaknesses, so watch out if you’re expecting a super effective Pokémon to do well, because it may face some unexpected resistance.
The last Pokémon the Team Star Boss will use is a Revavroom, but it isn’t any ordinary old Revavroom (although, watch out, because one Team Star Boss does use a regular old Revavroom)—instead it’s the Starmobile for that Team. This is effectively a special type of boss, as it isn’t really a Revavroom and has a much larger HP bar.
These Starmobiles have unique moves, different types and Abilities, and interesting strategies, so watch out! It’s important to remember that the Starmobiles are always of the same type as the Team Star Base, so even though you may see it as a Revavroom, it is not a Steel/Poison-type like Revavroom is.