This button leads to the multiplayer content of the game. There are two connection types available: Far Away and Nearby. Far Away allows you to play with other gamers from around the world, while Nearby restricts you to other Nintendo 3DS owners close to you. There are two multiplayer game types: Free for All and Light vs. Dark. Competing in multiplayer matches against other players or against the CPU can earn you hearts and special weapons.
The Gear button here works differently than it does in the Solo mode. Here, you can create up to 16 weapon/Power sets, allowing you to quickly switch between your favorite weapons and Powers between multiplayer matches.