Sidestepping (also known as "sidestep dodging", "spot dodging", "ground dodging", or simply "dodging") is a maneuver in Melee and Brawl that renders the character invincible for a short period of time (a slightly different amount for each character), performed by pressing down while holding a shield button. It can be employed to evade any and all attacks of short duration. Its main use is to avoid attacks with long cooldown lag, in order to stay close and counterattack.
Sidestepping is the shortest and fastest of the three dodges (rolling, side, and air). In Melee, it's also the only one that doesn't affect character movement.
Though the sidestep animation has the character leaning into the background or foreground, the invincibility frames gained dodge all attacks, including those that come from the foreground or background, such as the lava wave in Norfair.
Spot dodge frame list in Brawl
2-20 / 22 Link 2-20 / 22 Pikachu 2-20 / 22 Falco 2-20 / 22 Yoshi 2-20 / 22 Toon Link 2-20 / 24 Marth
2-20 / 25 Mario 2-20 / 25 Samus 2-20 / 25 Zero Suit Samus 2-20 / 25 Kirby 2-20 / 25 Fox 2-20 / 25 Mr. Game & Watch 2-20 / 25 Luigi 2-20 / 25 Diddy 2-20 / 25 Zelda 2-20 / 25 Sheik 2-20 / 25 Pit 2-20 / 25 Metaknight 2-20 / 25 Squirtle 2-20 / 25 Ivysaur 2-20 / 25 Charizard 2-20 / 25 Ike 2-20 / 25 Snake 2-20 / 25 Peach 2-20 / 25 Ganondorf 2-20 / 25 Ice Climbers 2-20 / 25 Wolf 2-20 / 25 Lucario 2-20 / 25 Ness 2-20 / 25 Sonic 2-20 / 25 Wario 2-20 / 25 R.O.B 2-20 / 25 Captain Falcon 2-20 / 25 Lucas
3-20 / 25 Olimar 3-16 / 25 Jigglypuff 2-20 / 27 King Dedede 2-23 / 30 Donkey Kong 3-24 / 32 Bowser