Metal Gear Solid: The Twin Snakes
March 09, 2004
A Mario and a Yoshi doll can be found in Otacon's lab. Shooting Mario makes the writing "1UP" appear while making the 1-Up sound. Shooting Yoshi causes him to say "Yoshi!"
Additionally, Psycho Mantis may mention Super Mario Sunshine during his battle if the player has a save file for that game in the memory card in slot 1.
Metal Gear Solid: The Twin Snakes was licensed by Nintendo to be released on the GameCube, so Konami was able to include references to Nintendo series, including Mario.