Directional influence (abbreviated DI) is the control that an attacked opponent has over his or her trajectory. It originated in the Super Smash Bros. series and can be performed in Super Smash Flash 2.
When an attack sends a character flying, directional influence can be used to alter the trajectory of the target. DI cannot reduce or negate the momentum of a move's knockback.
Much like in Super Smash Bros. Brawl, DI can be used to survive otherwise lethal attacks by adjusting the direction of the knockback towards the corner of the stage, instead of the closer edges. DI works by adjusting the direction of the knockback, not the speed; thus, when a character is sent flying vertically, pressing the down key will only make the character fly straighter vertically, reducing the distance they have to fly to reach the stage boundary. Likewise, pressing the side keys when a character is flying sideways makes the character fly straighter horizontally, again reducing the distance they have to fly until they reach the ledge.
When knocked vertically, pressing the left or right key will slant the trajectory of flight sideways, causing the character to fly diagonally. Similarly, pressing up or down when knocked horizontally will slant the trajectory of flight upwards or downwards, again towards a diagonal flight path. As the corners of a stage are further away than the sides of the stage, the momentum that would kill a character when sent flying straight up or straight sideways is survivable if directional influence is used to make the character fly towards the corners of the stage.
Smash directional influence
Smash directional influence (abbreviated SDI) is a mechanic that allows players to slightly alter their position during the freeze frames of being hit by an attack. To Smash DI, the player presses any direction of movement or the C-stick during the freeze frames to move the character slightly in which ever direction was input. SDI can be used to move into a wall or ceiling to tech, break out of combos, or move away from the blast line.
SDI is different from regular DI because the latter changes a characters trajectory in which he/she is launched in, while SDI changes a character's position before launch.