Place it under the whole underground section, then add the Enemy Spotted cue just before a hidden enemy appears and a Pop after a coin or secret is found, so the music carries the scene while the short effects mark each discovery.
关于此声音
This short instrumental is the bright, bouncy cave theme from New Super Mario Bros U Deluxe, with a lively melody and steady chiptune rhythm that plays through Mario's rocky underground stages. It feels cheerful, adventurous and lightly mischievous, turning a dark cavern into a playful hidden level. The tune comes from the Switch version's underground levels, where it replaces the usual overworld music.