Never heard of Shinobi III? Or Super Shinobi II? Or even the fact that there are prototype versions of this installment in the Shinobi series are available? Check here first as this introduction page complete with a built in FAQ will hopefully answer any questions you have and bring you up to speed.
The first prototype version of the game, which is the most interesting of the two available as this has vastly different levels, bosses, enemies and more compared to the final version that was released. Sadly most of the levels are incomplete (but can be finished) and the bosses don't work at all, but there is still a walkthrough if you want to see what the levels looked like along with many other features.
The original version of the game was never actually released, but it was sent out to various gaming magazines of the time for them to preview and even review in some cases. This version of the game is something that hasn't been found yet, but from the images collected from these magazines there is much to learn about it, including brand new levels and enemies that never made it to the final game.
The other beta version is much closer to the final product, seemingly almost identical at first -but the further you get into it the more noticeable it gets to how many changes were made, including completely different level layouts in certain stages, several glitches and unfinished areas. Again, there is a complete walkthrough to this beta along with sections on cheats for it and more.
Shinobi III: Return of the Ninja Master was finally released in 1993, and whilst an excellent game there were so many features cut out from previous prototype versions that it could have been even better if SEGA had kept some of them in. Anyway, this section of the site has a walkthrough to the game along with the usual extra stuff.