The Original Sin (Poison) comes from a portal in the bottom of the lead bucket with Primordial writing. The portal leads to the interior of the Folding Halls, into the poison pool chamber.
A primordial liquid magically summoned to a lead container within Depthsong Tavern. Upon consumption, the user makes a DC 20 Con save or takes 10d10 poison damage. Upon a success, they take half damage. If one fails the check by 10 or more, the user instantly dies.
The Vaakbonds use this for a number of activities, primarily as a dare between Duergar and as initiation into the family. Despite their poison resistance, its is still potent enough to kill, and those who consume Original Sin (Poison) and die get their illusory picture up on the wall of Depthsong Tavern.