Metal Mario

From Smash Bros - Wiki on Neoseeker

Metal Mario appeared in Super Smash Bros. in the 9th level of the 1 player mode. He was just a much heavier, faster falling and slower Mario who Kirby could not copy. Although he was never able to be used as a playable character without a cheating device, Super Smash Bros. Melee brought in an item that would make it possible. The Metal Box made your character metal, which in turn made Metal Mario playable when just using Mario in any mode. Metal Mario is also fought in Adventure Mode in Super Smash Bros. Melee, before fighting 15 Wire Frames and Bowser. If the player has unlocked Luigi, Metal Luigi is fought along with Metal Mario.