These are actually not Super Mario Bros Z characters, but rather Super Mugen Bros characters, as Shazzo said in readme file with this text string: "(character name) is one of the characters for Super Mugen Bros.". Also, Metal Sonic (not to be confused with Mecha Sonic) didn't appear in Super Mario Bros Z.
Unfortunately, all that we got from forgotten Super Mugen Bros game is all these characters (and Boo). All of these characters, as Shazzo stated are based on Actarus' (Not) CvS Axel Stone (which Shazzo confuses CvS Axel's author name with EasyChar). Also they look overpowered because of buf