Metal Luigi

Metal Luigi is the metal version of Luigi and brother or counter partner of Metal Mario. He has only appeared in the Super Smash Bros Series. Like other metal characters he is more powerful and takes less damage per hit. However he is heavier and slower causing him to fall off cliffs without comebacks more often. He can use the same attacks as Luigi as well.

Super Smash Bros Melee
In Super Smash Bros Melee metal Luigi appears in adventure mode along side Metal Mario. Before Luigi is unlocked you only fight Metal Mario. Metal Luigi and Metal Mario appear right before the boss battle with Bowser. The other way to see Metal Luigi is in battle if Luigi picks up a Metal Box he becomes Metal Luigi for a short time or you can set it to be natural from special match.

Super Smash Bros Brawl
In the Super Smash Bros Brawl Luigi must once again pick up a metal box to become Metal Luigi for a short time or set it to be natural in special brawl. He does not appear any other way in this game though.