To unlock it, you will have to defeat Scylla by building a Crossbow. All the Crossbow parts are available in Veil of the Forsaken and highlighted on the screen while the boss fight is active.

Defeating this enemy requires you to build a Crossbow using a Crossbow Arrow, Crossbow Base, and Crossbow Bow. All of these parts are found in the Veil of the Forsaken and are highlighted on the ...