Luigi Ladder is a technique in SSBM. 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.
The technique can still be performed to some degree in SSBB, but not the same way as in Melee. The sourspot of the Super Jump Punch produces hitstun in Brawl and as a result, will KO the other Luigi once they exceeded the upper blast line. As such, it can be used for recovery or even infinitely under a ceiling but it has lost its stalling capabilities since it can no longer be performed infinitely past the upper blast line. Two Luigis could waste some time by using the technique up to the upper blast line but this is impractical as both Luigis would be helpless which is made worse by Luigi's floaty falling speed and slow air speed, which easily sets up a powerful counterstrike from the opponent upon descent.