Not all Pokemon rush grass Pokemon Sword and Shield. Some take time to locate and you should do everything possible to add them to your location. For example, if you want to add Barpau and its evolution Milobellus to your Pokédex, you need to spend a lot of time fishing.
You can find Barpau in Pokémon Sword and Shield, but you don't have the best chance. It spawns on Route 2 and you need to throw your fishing rod into the water along the route to reel it in and fight it. Unfortunately, you only have a 1 in XNUMX chance of capturing it on this route. There are ideal fishing spots on this road west of the professor's house. To reach them, you must use the Rotom Bicycle upgrade in order to cross water.
This percentage chance means you have to spend a lot of time at a watering hole along this route to find it. Since it has a low probability, it's between level 37 and 40, so it's a decent battle. Barpau is a pure water type, so avoid using Electric and Grass types to fight him, so you don't knock him out. Once you capture it, turning it into Milobellus takes some work.
Add Milobellus to your Pokédex. You have the option of finding a Prism Scale and keeping it for the Barpau. While it contains the item, trade it with one of your friends and it should evolve into the Milobellus. I hope your friend has the good faith to offer it to you. You should have it in no time and add it to your collection and roster.
You cannot locate Milobellus in the water. You need to swap it with the prism scale.
Given how long this process can take, locating a Prism Stone and trading it with a friend seems like the best way to add Milobellus to your Pokédex.
