In Mario Golf, Metal Mario appeared as a playable character. His strength was more than any character's in the game, including Bowser's amazing strength. He was added, though, in the North American version of the game and cannot be found in Japanese versions.
Dr. Mario 64
Super Smash Bros.
In Super Smash Bros., Metal Mario was a boss in classic mode. He had his own stage that could only be accessed by hacking.
Super Smash Bros. Melee
In Super Smash Bros. Melee, if a player was Mario and he used the Metal Box item he could become Metal Mario. Also, when Metal Mario is fought, Metal Luigi also sometimes fights with him to make the match more challenging.
Mario Kart 7
Metal Mario reappears in Mario Kart 7 as an unlockable playable character in which he is listed as a heavy-weight driver.
Mario Tennis Open
Metal Mario reappears in Mario Tennis Open as an unlockable character in QR Code.
Mario Kart 8
Metal Mario returns to the Mario Kart series with Mario Kart 8. He now has a bit of personality with a distorted Mario voice and a mischievous tone.