From the Super Mario Wiki
Metal Luigi is the metal counterpart to Luigi who currently only made his appearance in Super Smash Bros. Melee, where he is 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 themseles 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.
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