Few NES games are shrouded in mystery as much as Punch-Out!! is. So many rumors as to the reason that Mike Tyson was originally tapped, then replaced and so on and so forth.
Originally an arcade game that eventually came out for the home console, it was at one point a vehicle for Mike Tyson and his budding (at the time) career.
Originally titled "Mike Tyson's Punch-Out!!" the game later did not include Tyson, as he ran into legal troubles.
It featured plenty of in-jokes, such as Donkey Kong as one of the spectators, and the producers of the game made no qualms about the fact that they were simply re-using characters, just rendering them different colors.
When Tyson's contract was not renewed, he was replaced with "Mr. Dream." The game didn't drop off in quality because of the change, but the game lost it's cache and became harder and harder to find.
It was an entertaining game, one that has recently been remade for the Wii. If only they could find a way to get Iron Mike back in the game, it would really take it to another level.