Deltarune is the indie role-playing game by Toby Fox that began with its first chapter in 2018, following the world of Undertale. Early in the story, Kris and Susie fall through a school closet door into the Dark World, a colourful alternate realm where ordinary objects become characters and battles play out in turn-based encounters. Fans have lifted the short falling sound from that transition for edits and short videos, because it instantly signals a shift from the everyday world to somewhere stranger. It remains useful as a compact, recognisable cue for portals, drops and dimension changes.