Punch-Out!! Game & Watch
September 03, 1984
The Game & Watch Punch-Out!! is actually an exact copy of Punch-Out!! only with its title changed on the console. Also the game's box shows an artwork of two boxers fighting, while the original box showed the game console.
Since the game itself is unchanged this is a type 1 link, because both versions feature the same characters, so we can say that characters originally from Boxing appeared in a Punch-Out!! game.
Notably, however, one of the characters on the box looks somewhat like Mr. Sandman, final boss of the original game, while the other might be a blonde version of the player's character or of Glass Joe. It's unknown if this was intentional, or if they were meant to be generic boxers, but either way they're assumed to be the same boxers as in Boxing.
Copyrights for both series are held by Nintendo.