How to Complete Lethean Draught

This quest becomes available after you have completed the game and after you have completed The Last Duelhorn.

The objective is to protect Maquis and defeat all foes. The foes are Dreamhares, and they can inflict Charm, so equip some protection against that if possible, and throw Knots of Rust at Charmed units to remove the Charm status without causing too much damage.