Original unmodified version of Shazzo's Metal Sonic. Originally made for never finished "Super Mugen Bros.", but erroneously called "SMBZ" characters (they have nothing common with the actual sprite animation itself, you guys better read the readme file). Like all of Shazzo's characters, this Metal Sonic is based on Actarus' "CvS" Axel Stone (or rather Shazzo's own Super Mugen Bros. Mario) but the moveset is different from his base so he's not exactly a spriteswap.
He was featured in "mugen mario bros. z mugen character pack" (sic), but Metal Sonic wasn't even featured in actual Super Mario Bros. Z at all (cameos and flashbacks notwithstanding), as we had Mecha Sonic there.