The bed: pad, bass, arpeggio
Three layers follow you everywhere: a flute pad doubled by chime, a bass line, and a harp arpeggio whose density tracks your movement. Standing still gets you two notes a bar; sprinting gets running 16ths. Tempo comes from what your body is doing (72 BPM still, 63 sneaking, 96 walking, 126 sprinting, 140 on elytra, plus 14 in combat) and it is eased in gradually rather than switched.
Tip: /score solo arp hears one layer alone, /score clear puts the band back.
The threat orchestra
Every hostile mob within 24 blocks that has line of sight on you adds its leitmotif to the mix, played positionally from the mob itself rather than from the music. Three motifs can sound at once and the highest priority wins the slots, so the creeper and the warden always cut through. The warden is the exception that ignores line of sight entirely, because so does the warden.
Tip: This is the whole mod: the spatial mix is a threat radar you listen to instead of look at.
The creeper swell
The creeper's line is chromatic, not in the key: four pling notes climbing a semitone each across the bar, so it never resolves and never blends in. Its volume ramps up as it closes on you, and inside 30 percent of the scan radius four more notes join in between the first four. The bar gets busier as the thing gets nearer.
Keys are geography
Your biome picks the key and mode. Deserts and badlands are E phrygian dominant, dark forests A aeolian, caves D dorian, swamps D dorian, oceans and beaches G mixolydian, snow G lydian, jungles C pentatonic major, the Nether F locrian, the End B phrygian, the deep dark A locrian, and mushroom islands whole tone. Crossing a border does not lurch: the new key has to hold for eight seconds, then the modulation lands on a phrase boundary with the pad dropping out for the pickup bar. Night darkens bright modes to aeolian at the next phrase.
Tip: Roots are laid out so neighbouring biome families sit close on the circle of fifths.
Percussion is information
The kit is completely silent when you are calm and assembles piece by piece as danger rises, with a snare fill into every phrase turnaround once you are in combat. Danger is a single number built from how many hostiles are near, how close, and how dangerous each type is; the four bands are calm, uneasy, danger and combat. Hostiles you cannot see still count, at 35 percent weight.
Tip: If the drums are building and you cannot see anything, something can see you, or is about to.
Stingers
Events interrupt. Taking damage fires a dissonant three-note pling cluster immediately, deliberately off the grid, because pain does not wait for the next beat. Killing a threat resolves the fifth down to the root on a bell, played at the corpse. Dawn is a rising flute figure and dusk a descending chime with a bass note under it. The first time a mob gets line of sight on you it plays its announce phrase, plus the vanilla note block mob-head sound.
Tip: Sightings share a 2.5 second global cooldown so a mob farm cannot machine-gun you.
The music breathes
After roughly 24 bars of calm the band takes a rest of 6 to 12 bars, fading out over four beats and back in over two. Resting is only allowed while things are genuinely quiet. Danger wakes the whole ensemble instantly, mid-rest, which means the music starting again is itself a warning.
Everything musical is JSON
Three files appear in config/thescore on first run: engine.json owns volumes, tempos, swing and thresholds, biomes.json owns the biome-to-key rules, and motifs.json owns every mob's leitmotif note by note. Edit, then run /score reload in game. No restart and no rebuild. A broken file never silences the game; the mod falls back to defaults and tells you which file failed and why.
Tip: /score demo <motif> auditions any motif on a phantom mob six blocks ahead for 15 seconds.