The phrase describes a type of fancy dress intended for celebratory events occurring on or around October 31st, wherein the wearer embodies the character of the famed plumber Mario, seemingly mounted upon the back of his dinosaur companion, Yoshi. This apparel typically involves a combination of visual elements to create the illusion of Mario actively riding Yoshi.
This specific costume design benefits from the immediate recognizability of the characters involved. The playful and interactive nature of the getup appeals to a wide audience, spanning children and adults alike. Historically, themed dress has served as a key component of this annual celebration, with depictions of popular culture icons gaining significant traction over time.