Undertale, released in 2015, introduced Sans as a seemingly relaxed skeleton with a famously demanding optional battle. Last Breath is an unofficial fan interpretation that expands his confrontation through multiple escalating phases, with Phase 3 representing a later stage of the encounter. Music and gameplay clips from the project circulated through fan videos, animations, remixes, and challenge runs. The audio remains recognizable because phase transitions, revived opponents, and extreme difficulty are enduring themes within Undertale fan culture.