Three scare levels, three different prompts
Halloween music splits cleanly into campy, creepy and kids. Campy is the party sound: surf guitar, a swinging organ, novelty cackles, lyrics about monsters doing the mash. Creepy is the haunted house sound: slow minor-key waltzes, theremin, detuned music boxes, tritones, whispered vocals and long silences. Kids' Halloween is bouncy and silly, with friendly ghosts, counting pumpkins and nothing that would frighten a five year old. Name the level in the first sentence of your prompt and the rest follows.
The musical shorthand for spooky is well established and the generator understands it: minor keys, 3/4 waltz time, pipe organ, harpsichord, theremin, tubular bells, pizzicato strings, a choir singing oohs, and a slow tempo between 70 and 100 BPM for dread or 120 to 140 for a monster dance party. Half-step melodies and a chromatic bass line add unease without any words.