I recently stumbled upon a note that early versions of the Sega Master System title Alex Kidd in Shinobi World featured a first-level boss named Mari-Oh. Intended to be a parody of Nintendo's Mario, much as Shinobi World is a parody of the popular Sega series Shinoboi, this boss was renamed "Kabuto" for the final release. However, the character retained some of Mario's qualities, namely fighting with fireballs and shrinking after taking damage.
Here are the only images of Mari-Oh I could find.
More than a passing resemblance, I think — especially to Mario's sprite in Super Mario Bros. 3.