She sings half a phrase and leaves it hanging over the shingle, and then she lets you finish it for her. Hit her hard enough and it snaps; leave it alone and it lands, sweetly, in her favour.
She names the exact number out loud — roughly an eighth of her maximum hit points, climbing by one every round, so a party that wants to keep forcing the sour outcome has to keep hitting harder to do it.
4d6+6 sonic in 9m, deafness, and a Fortitude save against being stunned — but she gets nothing at all out of it.
Nothing touches the party. Instead she heals a sixth of her maximum, hastes herself for three rounds, and hands every ally within 12m attack and saves. Every other conditional in this bestiary keys off the boss's own state; this one keys off the party's output, and she tells them the rule before it matters.
CR10, level with Nabb and Ogruk, one notch above the coast's prior Barknuckle ceiling.
She is the bestiary's first Virtuoso — the bardic-music prestige class, which advances real Bard spellcasting, so Bard 5 / Virtuoso 5 casts as a 10th-level bard and gets a genuine 4th-level list (Dominate Person, Hold Monster) rather than a stub. Goblin Coast already had a divine caster and a druid; a Charisma-driven arcane singer is a third distinct shape rather than a fourth of the same one.
The threshold is derived from her live maximum hit points rather than hardcoded, so the dilemma stays legible whether she is met at level 8 or level 14.
No epic spell: a 10th-level bard casting progression is nowhere near caster level 21.