To perform this glitch, go to the Stage Builder and build a stage consisting of a slope or two consisting of multiple slope blocks. Next, put the sideways elevators under each of the slope blocks like in the image. To go through the slopes, stand at an intersection between two slopes and perform a rolling dodge towards the elevator at the precise moment the elevator is under the slope and moving away. If done correctly, the character will roll through the slope and on to the elevator, possibly becoming stuck in the custom stage (depends on how it is built). In an alternative method, a character can be knocked through the slopes if hit by a strong enough attack (the attack doesn't need to be overpowering). This is most likely to happen in a V shape stage like in the images.
To escape, one would have to grab a warp star, obtain the three pieces of the Dragoon, hit someone or be hit with Ike's final smash, use Pikachu's final smash, Lucario's final smash, Snake's final smash, Olimar's final smash, or the Landmaster if you're one of the Star Fox Characters, or be sucked up by Kirby's final smash. An alternative method is to be hit through the slope's intersections to escape (it is much more difficult to get hit through the slope on the bottom side then it is through the top). This can backfire however, as seen in the Snake image below.