Plus button

The plus button (or + button) refers to the small button on the right side of the Wii Remote, Classic Controller, the button on the right side of the Wii U GamePad and Wii U Pro Controller, or the dark gray button on the right side of the Nintendo Switch Joy-Con and Pro Controller. On the Wii Remote, Classic Controller, Wii U GamePad, and Wii U Pro Controller, it matches the color of the controller shell

Overview
The + button is the equivalent of the Start button on other controllers, with the word "start" appearing below the button on some controllers. Its purpose in Super Smash Bros. Brawl,, and Super Smash Bros. Ultimate is to pause the game, start matches, and take snapshots for Brawl and For Wii U, as that feature was taken over by the Capture button in Ultimate. In the Subspace Emissary, the + button is used for Player 2 to space jump to Player 1.

Nintendo Switch hardware version 10.0.0 introduced the ability to map the functionality of any button to any other button from the console options menu, further diversifying how the + button can be used in Ultimate.