Ball warping is an advanced technique in super Smash Bros. Ultimate exclusive to Wii Fit Trainer. If the player uses Header directly under the lip of a stage, the ball will warp up through the stage and land on the ground harmlessly, hence the name. This technique essentially serves as another form of Header canceling, as it sets up the ball to be hit by the player once they get back onstage. After ball warping, an edge attack is the primary followup, sending the ball at a quick diagonal trajectory. This tech will only work on stages with slanted undersides, such as Battlefield. Ball warping was patched out of Ultimate in update 3.0.0.
A more drastic form of ball warping is a tech known as ball passing, so named because the player passes the ball directly through the stage.
How to perform
To perform the tech, the player must use Header while Wii Fit Trainer is pressed against the underside of a slanted stage, too low down for ball warping to occur. This will clip the ball inside the stage and keep it there. With this accomplished, the player must then use Super Hoop to hit the ball while it is still inside the stage's collision, consequently sending it up through the stage with an active hitbox. The ball can be hit in either direction depending on which way the player is moving with Super Hoop. When the ball is clipped inside the stage, Super Hoop is the only move that can be used to hit it, since getting into position for the tech requires the use of a double jump and Wii Fit Trainer falls too quickly to hit the ball with an aerial while it's still inside the stage. Ball passing was patched out of Ultimate in update 3.0.0 alongside ball warping. Ball passing is technically possible to perform in Smash 4, but the trajectory at which Super Hoop sends the ball is completely useless.