Potion of Poison
Property [Consumable]: As an action, you drink the potion. At the start of your next turn after you drink the potion, you take 3d6 poison damage. At the end of each of your turns in which you took damage from the potion, you make a DC 12 Constitution saving throw. On a successful save, the poison damage you take on your subsequent turns decreases by 1d6. If the poison damage is reduced to 0, the effect ends. A dispel magic spell or a greater restoration spell immediately ends the effect.
This potion appears to be another sort of potion, and it tastes and smells just like that potion. Sampling produces a sensation that mimics that of the other potion. A character who drinks the potion is racked with pain, as though from a dagger in the gut.