Lich dust

ingested (mixture) - 400 gp
MixtureThis black syrup with a slight taste of ashes can neutralize its victim in a few seconds. It is usually added to the food of the victim and a few drops are enough, which explains its low price for a mixture.
A creature subjected to this poison must make a DC 14 Constitution saving throw, taking 10 (4d4) poison damage on a failed save, or half as much damage on a successful one.
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  1. DnD 5e Poisons › Lich dust