The phrase in question refers to attire designed to replicate the appearance of the characters Mario and Luigi from the Mario Bros. video game franchise, specifically intended for wear during Halloween celebrations. An example would be a set of overalls, a red or green long-sleeved shirt, a white pair of gloves, a character-specific cap, and a stick-on moustache intended to transform the wearer into one of these iconic video game protagonists.
The appeal of such outfits stems from the widespread recognition and nostalgia associated with the Mario Bros. franchise. They represent a popular and generally family-friendly choice for individuals and groups attending Halloween events. Their historical context is rooted in the enduring popularity of the video game characters since their initial release and subsequent cultural impact on popular culture.