Contributed by gamemaster1991
The game was originally a Japanese only Gold Cart game that was won in a "Golf U.S." Tournament, where players would send in their high scores to Nintendo in order to enter the contest. The main difference between this and later copies of the game was that the final boss was Super Macho Man, and not Mike Tyson/Mr. Dream.
Contributed by DoubleYooToo
There is a hidden circuit in Punch-Out!! called the "Another World Circuit", which can be accessed by inputting the code 135 762 4680 on the password entry screen, then pressing A, B and Select simultaneously. The fights (in order) are King Hippo, Great Tiger, Piston Honda (Second Fight), Soda Popinski, Bald Bull (Second Fight), Don Flamenco (Second Fight), Mr. Sandman, Super Macho Man, and finally, a title bout with Mike Tyson/Mr. Dream, strangely labelled as "ANOTHER MCHAMPIONN." There is no extra content in this mode, but it does serve as a way to get to the later fights more quickly.
Contributed by DidYouKnowGaming
The Russian fighter Soda Popinski was originally named Vodka Drunkenski. They changed his name to avoid controversy.