Tormented Mandolin

Wondrous item, very rare (requires attunement by a bard)

This mandolin excels at bestowing overwhelming sadness and distress. Whenever you deal psychic damage while holding the mandolin, you can reroll any 1 or 2 you roll on the damage die; you must use the new result. A creature that attempts to play the instrument without being attuned to it must succeed on a DC 15 Wisdom saving throw or take 2d4 psychic damage.

Inspire Ruin. While holding the mandolin, you can use an action to expend a use of your Bardic Inspiration to cast the dissonant whispers or hideous laughter spell from it, using your spell save DC. When cast in this way, the target makes its saving throw against the spell with disadvantage.

Melody of Despair. While holding the mandolin, you can use an action to begin playing a sorrowful melody. You can continue playing until your concentration on it ends (as if concentrating on a spell), up to a maximum of 10 minutes, or until you're no longer holding the mandolin. For the duration, any hostile creature that enters a space within 30 feet of you for the first time on a turn or ends its turn there must succeed on a Charisma saving throw against your spell save DC; a creature automatically succeeds on the saving throw if it can't hear the melody. A creature can only make this save once per turn. On a failed save, the creature becomes wracked with despair: its speed is halved, it has vulnerability to psychic damage (unless it already has immunity to it), and it deals only half damage with weapon attacks that use Strength. An affected creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Once this property has been used, it can't be used again until the next dawn unless you also expend two uses of your Bardic Inspiration when beginning to play the melody.

The man in black strode to the tavern's stage with his mandolin in hand. A partial quiet came over the crowd, whose rowdy merrymakers couldn't be totally silenced.
With a few sullen strokes, the man surveyed the crowd with darkened eyes. His mouth barely moved, but everyone heard him say, "...Let's bring the mood down...by a lot."
Minutes later, the laughter and jeers turned to drunken sobs. The tavern keeper (who was also weeping) didn't mind, though: they sold just as many drinks, just for different reasons.