The underground theme comes from the original Super Mario Bros., released by Nintendo for the NES in 1985, with music composed by Koji Kondo. It became one of the most recognisable pieces of game music from the 8-bit era and spread far beyond the game through remixes, memes and retro gaming videos. Creators still use it because a few seconds instantly suggest caves, secret areas, side quests and classic platformer nostalgia, even for viewers who have never played the full game.