Version differencesMario is Missing! was originally developed for PC as a point and click edutainment adventure, similar to Carmen Sandiego games, however the SNES does not lend itself well to that type of gameplay, so instead runs on the Super Mario World engine and allows similar action.
WeegeeMario is Missing! is very famous for its sprite for Luigi (although most people refer to him in this game as "Weegee"). Weegee is still used in video-game related jokes today. You can only see Weegee in the DOS version of the game.
Mario licenceMario is Missing! is the first title in which Nintendo allowed another company to use their characters on a machine not produced by Nintendo.
Information also contributed by Arejarn