D&D 5.5e Dungeon Master's Guide
Poison
Varies Arcane, Divine, Transmutation
A creature that ingests Midnight Tears suffers no effect until the stroke of midnight. Any effect that ends the Poisoned condition neutralizes this poison. If the poison hasn’t been neutralized before midnight, the creature makes a DC 17 Constitution saving throw, taking 31 (9d6) Poison damage on a failed save or half as much damage on a successful one.
An enigmatic origin for this deadly and magic poison can be traced back to followers of The Secret Keeper. It's jet black ink like appearance turns clear as water when it's ampoule is opened. Most who have ingested midnight tears have not lived to tell others of it.
Cost: 1,500 gp
Weight: .2 lbs.