Mike Inglehart, one of the directors of the Wii game, is the voice of Super Macho Man.
Matt Hardy and Scott MacFayden, the game's sound crew, provide the voices of Little Mac and King Hippo respectively. (Although the voice is of course heavily distorted in MacFayden's case)
Development Gag: The gaming studio that developed the Wii version is located in Salmon Arm, British Columbia in Canada. Which is where they decided to have Bear Hugger—and even named one of his moves—from.note He's actually from Saskatoon, Saskatchewan, at least according to the Super NES game.
Great Tiger in Title Defense mode makes several illusions of himself between rounds. They hang out on the ropes talking like they're on break.
Doc Louis and Mr. Sandman are both voiced by Riley Inge. These two characters are also the only ones that refer to Little Mac as "Mac baby".
Unintentional Period Piece: The NES game, with Mac's pink track suit, Popinski being from the USSR, Great Tiger's hometown being named "Bombay", and Mike Tyson being champ definitely set it in the '80s. If Mac's able to beat Super Macho Man, the player will see a paper that gives the date as April 1, 1987.
Mac in the SNES Super Punch Out is blonde and tan for unknown reasons but beta footage shows him looking far different.
Bear Hugger was originally going to appear in Mike Tyson's Punch Out, but was replaced with King Hippo.
Mario's cameo was going to be kept in Wii, but they couldn't make him fit in with the game's art style. Instead, they opted for a generic referee.
The original game was originally called "Knock-Out!!", which was the name used for most of development and when the game was shown at trade shows in America during 1983, but it was renamed before release. Takeda was also experimenting with the use of a glove-based controller for the game, but Miyamoto didn't like ambiguous interfaces, so the joystick and buttons were implemented instead.
When the arcade Super Punch Out was being conceptualized, the team had the idea of giving the boxers weapons, but eventually settled on the use of illegal moves.
In an interesting coincidence, the initial barrage of punches Mike Tyson hammers you for in the NES version lasts 91 seconds, the amount of time it took Tyson to knock out contender Michael Spinks in 1988.
Likewise, in real life, Mike Tyson's first loss to Buster Douglas in 1990 occurred by way of knockout, with Mike Tyson toppling backwards and collapsing next to the ropes with his arms flailing to his side in a manner reminiscent◊ of the way he goes down in the game◊.
The only boxers to appear in all three console versions of the game are Bald Bull, Super Macho Man, and Mr. Sandman. Due to Arcade Super Punch-Out being a Mission-Pack Sequel, no boxer has appeared in all games.
In the NES version, a camera held by an audience member at the top-right corner of the screen will flash when Bald Bull's bull charge can be countered.
In the same vein, an audience member who looks like they're wearing shades will frown with their mouth open right before Super Macho Man throws his sudden clothesline punch, making the attack easier to dodge.
Little Mac (or someone that looked like him) was going to be the player character in the SNES Super Punch-Out!! before being replaced by the blond boxer for unknown reasons. Nintendo has flip-flopped over whether this character is Mac with a makeover (as they said he was when he guest starred in the Gamecube version of Fight Night Round 2) or an entirely new boxer for several years.