How to perform
The player should get close to the ledge, and tap as fast as possible towards the ledge. One way to do it is to hit the control stick to the desired direction, while letting one's finger slide off so the control stick returns to its original position. The character will start a dash for one frame without falling off the edge of the platform.
If the player is using a GameCube controller or Classic Controller, they can use the C-stick or to perform a dash attack next to an edge. It is done by hitting the C-Stick any direction but upwards right after the control stick is tapped. The player doesn't have to let go of the control stick this time, they just have to make sure the C-stick comes right after the left control stick.
If the player tries to use the A button instead of the C-stick, they'll perform a f-smash. If the player is using the C-stick and the character performs a d-smash, then the C-stick was hit too soon.