Two pretty fast ways to do this one. Have both players make characters with Start Dash A, B, or C (preferable A) and play SPECIAL Versus Player Match. Set Battle Time to 80 and Battle Count to 5. First way, have one player run forward and the other backward. Once at the edge of the level, switch roles then repeat. Second way, Have one person run to the center of the stage, then the other person pushes up or down on the left stick. Takes time but its pretty damn fast.