L button

The L button refers to the left shoulder button on the Nintendo 64 controller, GameCube controller, and the Nintendo 3DS, as well as one of two left shoulder buttons on the Classic Controller, Wii U GamePad, Wii U Pro Controller, New Nintendo 3DS, left Joy-Con and Nintendo Switch Pro Controller.

Overview
The functionality of the L button has changed throughout the series. On the N64 controller, it is used for taunts. On the GameCube, Classic, Wii U Pro controller and Wii U GamePad, it is used for shielding, rolling, air dodging, and spot dodging (which are actions shared with the R button) while on the 3DS, Switch Pro and dual Joy-Cons, it is used to grab. Outside of gameplay, the L button is used to navigate some menus like tips and move lists.

When using a single Joy-Con in Ultimate, the L or R button (depending on which Joy-Con is used) is not set to any action by default. Instead, the SL button is used in its place and is used for grabbing. In this configuration, the L, R, ZL and ZR buttons cannot be set to grab.

In Super Smash Bros. Brawl,, , and Super Smash Bros. Ultimate, the L button can be customized in the controls menu to perform other functions. It should be noted that the 3DS version has the ZR button perform the same functions as the L button due to the game releasing before the New Nintendo 3DS introduced a ZR button to the system. Prior to version 1.0.5 of the game, these buttons' functions were reversed, so ZL would trigger the same actions as L, though their functions outside of battle (such as in menus) were the same as in current versions. 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 L button can be used in Ultimate.

Trivia

 * Masahiro Sakurai had proposed the L and R buttons on the GameCube controller be replaced with a scroll wheel, as he believes that would be the ideal method of menu navigation.