Vexation

The first time the party leave Coalition Camp, they'll be ambushed in a anti-magic zone to pit fight several mercenaries led by a Shadowy Figure hired by Jon Irenicus. Gorion's Ward may manage to kill one of these powerful figures and get Vexation, but against several of them, all are powerless, the party will be captured, as seen in the ending scene, then tortured, beginning the events of Shadows of Amn.

In-game description
"This blade appears smooth and whole at first glance, but on closer examination, its surface is made of thousands of tiny overlapping scales. When the sword is used to stab a target unawares, scales break off and lodge in the wound, irritating the victim and draining their strength."