Shake Smash

Shake Smash is a function in Super Smash Bros. Brawl that allows the player to shake the Wii Remote to do a Smash attack. It's an extra option and requires the user to make a name to customize controls in order to activate it (it's deactivated by default). It can be only used with the Wii Remote and Nunchuck combo control scheme.

How it works
The Shake Smash is a mapping of the A button (held) plus the direction the remote is swung. For example: A side shake will result in a Side smash, a vertical shake (to up or down) will result in an up smash and down smash, respectively. It works very well from 90 to 95%, but sometimes it needs an exact swing of the remote (in side smashes) from left-right or right-left to do the attack in the direction of the opponent.

As the Shake Smash function is only a mapped A button, it can be used for many things that require the A Button as well, such as throwing after grabbing an opponent, or throwing an item. These actions as well detect the direction the remote is shaken. Oddly, it also works in some Final Smashes that use either the "Attack" or "Special" (A or B usually) without distinction, to attack (For example, Konga Beat, or, in a stranger case, Grenade Launcher, which means that players can shoot grenades by shaking the remote).

Origins
The Wii Remote's motion sensitive functionality, while downplayed in Brawl, is actually one of the main selling points of the console. Many other games feature motion sensitivity in big ways.

Originally, Super Smash Bros. Brawl was not intended to use any motion controls, as Nintendo president Satoru Iwata put it, it would get in the way of the game, or otherwise, it would feature very minimal integration.

During development, designers tried to find ways to integrate the Wii Remote. One of the ways was using the Remote to perform Taunts but it was finally decided to use the motion sensitivity to perform Smash attacks.