Pokémon have always had various ways of evolving into new beasties, and Pokémon Sword and Shield are no different. One of these curious contenders is the monochromatic Galarian Zigzagoon, which can be found all over the Wild Area, but you're better off looking on Routes 2 and 3. They're not hard to find, and in the Wild Area you may even find a Galarian Linoone as well.
Evolving Galarian Zigzagoon into Galarian Linoone is easy, you just need to get it to level 20, but getting a Galarian Linoone to become an Obstagoon isn't quite as straightforward.
You're going to need to get it to level 35 at the very least, but that may not make it evolve, because this thing can only evolve into an Obstagoon at night. Simply level it up using a Rare Candy or any other method once the sun is well and truly down, and you'll have yourself a beautiful black and white Obstagoon at your command.