Mario being the referee was added at the last minute. While Nintendo owned Punch-Out and there was no legal issue, apparently the creators forgot to ask their bosses permission to put the plumber in the game.
Ten thousand Japanese fans who submitted high scores to a golf game were given gold colored cartridges with Punch-Out. Though Super Macho Man was the final boss, not Mike Tyson.
In later versions of Punch-Out on NES, Mike Tyson is cosmetically replaced by a boxer named Mr. Dream. Most assumed it was Nintendo distancing themselves from his criminal history, but it was because he lost his championship title.
Many found it odd that Solid Snake fights a super computer instead of a Metal Gear in the NES version of the original game. The reason was mainly technical, as programmers couldn’t fit the nuclear tank properly with the limitations of the hardware.
Hideo Kojima was not pleased with the NES version of Metal Gear. They made combat more the focus rather than stealth, and he was definitely unhappy that the Metal Gear boss fight was replaced by a super computer.