If you're looking to evolve Qwilfish into Overqwil in Pokemon Legends: Arceus, then you'll need to know exactly what to do to trigger those evolution criteria. Like some of the other critters found in the Pokemon Legends: Arceus Pokedex, it requires using a specific move a certain number of times.
It's one of the new evolutions for the game, and you'll only be able to get Overqwil by evolving a Qwilfish - there's no alternative route for this one. Plus, it's a crucial Pokemon for solving the Pokemon Legends: Arceus Sea's Legend mystery, so you'll need it too.
Here's how to evolve a Qwilfish into Overqwil so you can use it in battle.
1. Find a Qwilfish
Before you can start evolving, you're first going to need the base Pokemon - Qwilfish. This can be found at a few locations across Hisui - Ramanas Island in the Obsidian Fieldlands, and then Tranquility Cove, Lunker's Lair, and Islespy Shore in Cobalt Coastlands.
2. Make sure it has the move "Barb Barrage"
Once you've got your chosen Qwilfish - hopefully a powerful Alpha - you'll then need to make sure it has the move Barb Barrage. It's using this move that's going to allow you to evolve your Qwilfish into Overqwil.
Make your Qwilfish use Barb Barrage in Strong Style 20 times in order to make it capable of evolving.
If your Qwilfish doesn't have Barb Barrage and it's quite high level, it might be that it has already learned it but not added it to its rotation in the wild. To check, go to your Qwilfish in your party, press A, and then go to Change Moves. You may well find Barb Barrage in here and be able to switch it in.
3. Evolve your Qwilfish into Overqwil
Once you've unleashed 20 Strong Style moves of Barb Barrage, you'll be told your Qwilfish is ready to evolve into Overqwil. Congratulations!