Perrserker Pokémon GO is one of the new Galarian Pokémon introduced as part of the Throwback Challenge Champion event.
Perrserker Pokémon GO: How to Catch
Perrserker is the evolved form of Galarian Meowth. Not to be confused with the Alolan Meowth, the Galarian Meowth is round scruffy Steel type variant of the classic Meowth. Instead of evolving into Persian like its other regional counterparts, Galarian Meowth evolves into a different species, Perrserker. Meowth is unique in that it is the only Pokémon to have three regional forms.
Galarian Meowth can be caught as a reward for the Throwback Challenge Champion special research. You'll be able to find them in the wild and can also hatch one from 7km eggs during the event.
Once you've obtained a Galarian Meowth, you evolve it into Perrserker with 50 candy, much like the other Meowth versions.
Perrserker itself is rather unique: it's a pure Steel type Pokémon with a varied move set. It's best moves aren't even Steel type, so it doesn't get any bonuses for them. It does allow Perrserker to cover a variety of threats, and the bulkiness from the Steel typing gives it it's own niche to fill.
Perserrker works well in the Great League before it's outclassed by other Steel types like Metagross in the higher CP brackets.