Cave Story's Secret Santa is set after Balrog recovers Christmas presents stolen by the Mimiga Chaba. The task of delivering them falls to Santa — a cowardly Mimiga who must now sneak into every home and return the missing packages without waking anyone. Santa tiptoes past sleeping residents and evades patrolling Gaudi through a series of stealthy infiltration levels, eating cookies left out by households along the way and placing gifts under trees where they belong.
The gameplay emphasizes quiet problem-solving: Santa can push or pull obstacles, flip light switches on and off, pry open ventilation shafts, and use the environment creatively to avoid detection. Making noise risks attracting attention and failing the mission.