Editing Smash directional influence

[[File:SDI_Snake_Brawl.gif|thumb|200px|{{SSBB|Snake}} using SDI against {{SSBB|Captain Falcon}}'s [[Knee]].]]

The mechanics of SDI operate by shifting the character by a vector determined by the control stick. SDI is applied on every frame a control stick vector of sufficient length is input, in a new direction on either horizontal or vertical axis. As a result, repeatedly tapping in one direction will move the character much farther than simply holding the stick in that direction. In addition, because diagonals have both horizontal and vertical components, changing from an orthogonal position to an adjacent diagonal one will generate a new SDI input, while changing from a diagonal position to an adjacent orthogonal one will not. This results in a technique called '''quarter-circle DI''', which involves quickly rotating the stick between two orthogonal positions for increased distance. Quarter-circle DI was introduced to the United States by Japanese smasher {{Sm|Captain Jack}} and was once known as Japanese DI.

In ''Brawl'', the C-stick can assist in SDI. So-called '''double-stick SDI''' utilizes the C-stick's ability to override the control stick by holding one of the sticks in one direction and utilizing quarter-stick DI with the other.

Whenever a character is hit on the ground by an attack that does not lift them off it, such as a weak [[meteor smash]] or move that launches at the [[Sakurai angle]], they can only leave ground horizontally, not vertically. This prevents them from SDIing upward and going airborne before getting launched by the attack, potentially allowing them to immediately land and cancel [[hitstun]]. When grounded, the horizontal component of a diagonal SDI vector still moves the character, only vertical component is negated. Consequently, quarter circle SDI and other methods to perform multiple SDI inputs still work. In ''Ultimate'' when hit with a move that will lift the victim off the ground, it is possible to SDI upwards only if the first SDI input is made on exactly frame 2 of hitlag, and it is in an upwards direction. Doing so lifts the opponent off the ground during hitlag, allowing for further upwards SDI inputs to be made. Notably, this allows opponents to jump out of fast hitting moves such as {{SSBU|Ryu}}'s down tilt which would otherwise force a landing during hitstun, before hitting the ground, as they will be launched from higher up, and thus the hitstun will end before they land. However, due to the frame perfect timing required, which also demands a correct prediction of what move will hit the victim and on what frame, this has little to no utility in realistic circumstances. The opponent can still SDI off the grounds when hit by an [[electric]] attack.

'''Automatic smash directional influence''' ('''ASDI''' for short) is a weaker variant of SDI. Once a character's hitlag is over, they shift slightly in whatever direction the control stick is currently held, by a shorter distance than an SDI input. If the C-stick is also being held in a direction, it will override the control stick's input, allowing the player to [[DI]] in another direction simultaneously. ASDI is significantly less useful than regular SDI and is generally ignored, as any stick position during this time is likely to be attempted at regular DI. In ''[[Super Smash Bros. Melee]]'', however, it is an important factor in [[crouch canceling]]. It is often used in place of crouch cancelling against moves that have the [[Sakurai Angle]], such as the weak hit of Marth's [[Dolphin Slash]], as at specific percents they are impossible to crouch cancel. The downward shift from ASDI down may allow a character to land on the ground immediately. If the character wasn't knocked down, the landing cancels hitstun, and thus allows them to retaliate against attacks much quicker than usual. It is additionally key in utilizing techniques like [[Tech#Rolling_tech|Amsah techs]] and [[Slideoff DI]], which use ASDI to create tech scenarios and escape combos respectively.

Because of the significant [[nerf]]s to SDI in ''Smash 4'', there are few attacks against which it is noticeably effective, such as {{SSB4|Ryu}}'s light [[up tilt]], and most infamously {{SSB4|Bayonetta}}'s [[After Burner Kick]] and [[Witch Twist]] beginning in update [[1.1.6]], due to their SDI multipliers of 2.5× and 2× (respectively), long hitlag, and ability to otherwise lead into guaranteed combos that can both rack up significant damage and KO. Despite the nerfs however, SDI can still be effective in escaping long combos, such as with the game's notorious [[ladder combo]]s, as even the decreased distance of SDI can be enough to push a character out of a followup move's reach, especially after SDIing several consecutive hits. ASDI and shield SDI have lost most of their practical usefulness due to their even shorter distance, especially the latter due to not being affected by SDI multipliers that could otherwise increase its distance, though again there are situations where they can still make a difference.

*ASDI has been removed almost entirely, only applicable on moves with an electric, [[paralyze]], or [[crumple]] effect, and a special attack effect only used for [[Kazuya (SSBU)|Kazuya's]] 10-hit combo, further limiting its application. Oddly enough, it now applies twice against moves with these effects. It also oddly still seems to apply for [[Final Edge]].

As a result, while SDI remains more limited in utility compared to the pre-''Smash 4'' games, it is generally more effective for escaping long sequences of multi-hit attacks than it was in ''Smash 4'', and the general greater prominence of long combos in ''Ultimate'' has also increased its utility compared to ''Smash 4''. Much like DI gaining a visual indicator in the form of a bright blue streak of light, SDI has gained a visual indicator manifesting itself in the form of a crescent shape angle reader when performed, allowing players to see which direction their opponent is going, though this is generally too quick for players to react to except for with moves that have extremely long hitlag, such as with {{SSBU|Samus}}' [[Samus (SSBU)/Neutral special|Charge Shot]].