Union Circle codes are unique identifiers used in Pokémon Sword, Shield, Brilliant Diamond, and Shining Pearl on Nintendo Switch, connecting players for multiplayer experiences. Through the Union Circle hub, players can share Union Circle Codes, Link Codes, Trade Codes, Battle Codes, and Raid Codes to access various multiplayer modes. These include local and online trading, battling, and cooperative Max Raid Battles, where players team up to defeat powerful Pokémon. Players can find and connect with others through friends lists, the internet, or by sharing codes to build competitive Pokémon teams and engage in exciting multiplayer challenges.