Metal Luigi

Metal Luigi is the metal counterpart to Luigi who makes an appearance in Super Smash Bros. Melee, as a mid-boss, and Super Smash Bros. Brawl, as a playable character and a mid-boss. He appears with Metal Mario.

Super Smash Bros. Melee
In Super Smash Bros. Melee, Metal Luigi is one of the game's mid-bosses encountered before the final boss, Bowser. He appears in Adventure Mode, alongside Metal Mario. Once the player has unlocked Luigi, Metal Luigi makes the battle harder, because instead of battling one metal brother, the player has to battle the two metal brothers, who gang up on the player. Like Mario's metal counterpart, Metal Luigi is heavier than the regular Luigi and uses the same moves as his counterpart. Additionally, players can pick up the Metal Box item, turning themselves into metal forms, boasting the same attributes as Metal Luigi and Metal Mario.

KOing both the Metal brothers in Adventure Mode awards the player 8000 points.

Super Smash Bros. Brawl
Metal Luigi appears as a playable character, a mid-boss, and a power-up in Super Smash Bros. Brawl. He is playable in Metal Brawl, and playable when Luigi uses a Metal Box in any mode.

Super Smash Bros. for Nintendo 3DS/Wii U
In Super Smash Bros. for Nintendo 3DS / Wii U, Metal Luigi is also if, when playing Special Smash, the Metal setting is on, or temporarily when Luigi uses a Metal Box. Also, in the games' Classic Mode, sometimes a character that has either the Giant or Metal takes place of another character. A Metal Luigi might appear as one outcome, acting as a pseudo mini-boss.

Trivia

 * In New Super Mario Bros. 2, Luigi's body turns to silver when he collects a Gold Flower and transforms into Silver Luigi, making him look similar to his metal form.