Little Mac is pretty well a textbook example of an underdog. He’s 4′ 8” and wants to be a world champion boxer. So he finds a trainer and works his way up the ranks, routinely fighting folks over twice his size… or more. The game is a little less polished than the Super NES version, but the main thing that’s different is the, for lack of a better term, heart system. You start out with a set number of hearts, each one representing a punch you can throw. If you connect with the punch then the meter stays the same. If you miss, the punch is blocked, or get hit by your opponent’s punches you lose hearts. Lose all of them and you temporarily lose the ability to mount any kind of offense until the regenerate. That’s pretty inconvenient.
The game culminates with a ridiculously tough fight against Mike Tyson (Mr. Dream in later versions). He was actually the only fighter I could never beat. I was able to play the entire game and get to him without getting so much as knocked down and then would have my head handed to me soundly every time. I even resorted to putting in the ’secret’ code so many times that it’s indelibly etched into my brain (007-373-5963).
So I consider the game to end when you beat Super Machoman, and the Tyson fight an optional boss-fight. This also means that I’ve never actually seen the ending, but I understand that I’m not really missing that much.