Bidou (微動, fine movement) refers to a control scheme used exclusively for Super Smash Bros. for Wii U. By moving a controller's right control stick while holding down corresponding button inputs, it is possible to register a left control stick input for only one frame. This makes many advanced techniques that would otherwise require frame perfect or precise inputs to be performed easily.
There are three known right stick configurations that allow for Bidou, all of which require a button and the right stick to be set to the same input.
Because Bidou involves the use of both control sticks at the same time, it is common to set the shoulder buttons to Shield, Attack, and Special Move, and either turn on Tap Jump, or assign Jump to a fourth shoulder button if it is available. Therefore, it has varying levels of compatibility with controllers:
With Bidou, the player essentially gets access to two smash directional inputs, which makes frame perfect inputs possible and makes full use of techniques such as perfect pivoting, extended dash-dancing, and reverse aerial rush. With perfect pivoting, it becomes much easier to crouch during one with Bidou, due to the right stick supplying the pivot input, allowing the crouch to be done with a simple quarter-circle motion downwards with the left stick, rather than the precise inputs required by default. Perfect pivot crouches allow a character to space with more precision (similar to wavedashing), sidestep during a perfect pivot (if Shield and then down are inputted after the perfect pivot), and safely approach at lower percents, since crouch cancelling still exists to a lesser degree in Smash 4. Extended-dash dancing and reverse aerial rushes can be pushed to the limit with Bidou, as alternating the sticks at the same time for extended-dash dancing tightens the character's oscillation (even for characters who would normally gain little benefit from extended-dash dancing with just the left stick over alternating fox-trots, such as Luigi or Sheik), and reverse aerial rushes can be done simply by holding the left stick forwards, flicking the right stick in the opposite direction, and immediately jumping and attacking, leaving less room for lag in-between the inputs. Some character specific techniques are opened up with Bidou; instant ledge wall jumps allow for safer ledge trump edgeguards, as they do not use up the midair jump, but can only be done on a few stages, particularly on stages with a wall under the ledge, such as Duck Hunt. Fast fall ledge trumps involving item drops are still complicated but are nevertheless easier to do with the right stick, as the right stick input down can be used as the fast fall input.
Other frame perfect techniques that are made easier include slow runs (which would otherwise require precise control with the left stick), dashes out of walking animation (which would otherwise leave a few frames of lag, like reverse aerial rushes), pivot and attack out of interruptibility frames (which might otherwise cause the character to do a dash attack the other way instead of the attack desired, such as a down tilt), dash attack near the ledge (which might cause the character to careen off the ledge and aerial instead), and instant forward roll out of a character's running animation. The last technique in particular is only possible with Bidou, as unlike a forward roll after an initial dash, only one of two things can happen; either the shield will appear before the roll, or the character enters the skidding animation from stopping the run and can only jump out of the animation.
Bidou takes advantage of the way inputs are handled in Smash 4. Normally, a right stick input is treated as a 1-frame simultaneous input of a directional input of the appropriate strength and either Attack or Special Move, depending on what the right stick is set to. If the corresponding button input is held down, however, the additional Attack or Special Move right stick input is ignored, and only the 1-frame directional input is handled by the game. By holding down the buttons when they will not result in an action, the right stick can then be used as a special directional stick that registers 1-frame inputs only.
Bidou was brought into the spotlight by My Smash Corner from a video previously uploaded by a Japanese smasher. My Smash Corner claimed that Bidou had the potential to affect the metagame, assuming players could master its capabilities. Bidou is a unique method of playing Smash, since it requires a dedicated control scheme, and involves holding down buttons for extended periods of time, an input that is otherwise unheard of in Smash. It is currently unpopular in terms of usage among most players attending tournaments, due to the difficulty and dedication in having to adapt to the unique control scheme, particularly for Smash veterans who have played with relatively unchanged controls for years. Nevertheless, it has gained some attention, due to hosting a variety of unique advantages compared to regular control schemes, and a number of players have been known to use Bidou in tournaments, such as ESAM when he plays Pikachu.
Practically, the difficulty of consistently executing Bidou-specific techniques does not make up for its advantages, and no major tournament has ever been won by a player using Bidou.
Officially, Bidou is not banned, and all tournaments allow players to customise their controls before a set starts. Bidou, however, derives most of its benefits from use of either the Wii U Pro Controller, the Wii U GamePad, or the Classic Controller, and all three controllers are generally banned in large tournaments for a number of reasons; the Wii U GamePad's inability to be transferred from console to console prevents two players who prefer the GamePad from playing, and both the Wii U Pro Controller and Classic Controller require syncing and unsyncing from the Wii U console, potentially leading to time constraints and other logistic issues at large tournaments.