Luigi Ladder

From SmashWiki, the Super Smash Bros. wiki

Luigi Ladder is technique (sometimes referred to as a glitch) in SSBM and SSBB. It involves using 2 Luigis' Up Special Moves constantly against each other, with each Luigi using his Super Jump Punch after the other Luigi gets hit with the attack. They can constantly go up until they reach the blast line. This does not cause a KO because unless sweetspotted, the attack causes no knockback or hitstun.

The Luigi Ladder is banned in tournament play, though this, of course, is only significant in doubles. Since Friendly Fire is turned on in standard tournament rules, a team of two Luigis could execute the technique, creating an essentially unbeatable stalling technique.