Deltarune is Toby Fox's follow-up to Undertale, with its first chapter released in 2018 and later chapters expanding its story of Lightners and Dark Worlds. In the game, a dark fountain is a towering column of darkness that, once opened, transforms an ordinary room into a Dark World filled with new characters and rules. Clips of its distinctive sound spread through fan edits, gameplay videos, and meme compilations on video platforms, where it became shorthand for entering another world. It remains popular because the sound is instantly recognisable to players and adds instant drama to a reveal.