Alex Kidd was not originally intended to be the star of the game, but in fact an original character called Shinobi Kid. Apart from a few sprite character changes and some graphical alterations to the first level, the games appear to be identical. but no Images or Sprites of Shinobi Kid remain in the Shinobi World ROM. The first boss, Kabuto, was originally going to be named Mari-Oh, as a parody of the Nintendo character Mario (“Oh” in Japanese meaning, “King”, King Mari). Despite the name not going through, Kabuto still shares many of his would-be counterpart’s qualities; his main attack is shooting fireballs, and he shrinks after taking a certain amount of damage.
Rumor has it that Sega also originally intended Alex to appear in several games parodying their own licenses in a bit to re-invent the character, with Golden Axe and Phantasy Star on the top of the name list. Unfortunately, Sega’s success on Sonic The Hedgehog put an end to this plan. – [info from Wikipedia]