The crossbow has never been considered an elegant weapon and the Lords of the Understreets haven’t done anything to improve its reputation. In recent years, their adaptation of a basic tracking spell has made these projectile weapons much more lethal.
Being found in the possession of a crossbow and what is now commonly called “tracking bolts” carries a minimum two-year sentence in the Vasteel Dungeons.
After hitting a target with a Tracking Bolt, you can speak a command word to mark the location where the bolt hit. You gain Advantage on all subsequent Ranged Attack Rolls made against the marked target when using Tracking Bolts.
Additionally, other friendly creatures can use your mark to gain Advantage when firing their Tracking Bolts at the target and similarly you can use their marks. If more than one marked target is within 30 feet of another marked target, the advantage is lost.