Bonefiddle

You rub your middle finger across your thumb like a bow against a fiddle while humming a discordant tune under your breath.

You call up a ghostly fiddle bow in the air above a target creature in range.  This bow immediately descends into the target's body and begins to saw back and forth against its skeleton, creating a discordant melody.  The target has disadvantage on Dexterity (Stealth) and Wisdom (Perception) checks that rely on sound while the melody plays.  At the beginning of each of the creature's turns, it must make a Constitution saving throw.  It takes 2d6 thunder damage on a failed saving throw.  On a success, the target takes no damage and the bow emits a harsh plucking sound as if a violin string has broken.

After the target is reduced to 0 hit points or succeeds on its saving throw, you may choose a new target in range as a bonus action. You may not target a creature that you have already targeted with the spell previously.

Creatures that lack skeletons or exoskeletons are immune to this spell.