Hag's Bargain

Obtained by Vincenzo in the top floor of Old Bonegrinder, near the Tome of Strahd.
Described as a "Hag's Bargain" by Anya Avicenna at Avicenna's Augury in Vallaki. Hags collect bargains from those they encounter and store them in skull-shaped glass vials. They contain such esoteric things such as your joy, your happiness, your memory, your voice, etc.