This is Blitzle. It was left out of Pokémon Sword and Shield despite also being left out of Gen 7 unless you transferred, a fate it shares with a number of other Pokémon such as Stantler, Furret and plenty of others. Meanwhile some Pokémon like Hawlucha and Vanillish have remained obtainable in-game throughout the last few gens. Say something nasty to Masuda for not understanding the concept of variety in what he chooses to make available in each game.