After boarding the boat from the Underdark beach, a boat captained by Corsair Greymon will sail up alongside the party's boat. Greymon will come aboard, and the player character will have to pass a check or attack Greymon and his crew consisting of:
Passing a DC 15 Athleticscheck to push him into the water will kill Greymon, sinking his inventory to the bottom of the sea and making it permanently inaccessible, while initiating combat with the surviving Duergar; this will also garner approval from Lae'zel and Astarion. In a chest aboard Greymon's skiff is the Intransigent Warhammer. If pushed into the water during battle, he and his crew will wash up at the beach near the southern pier at the Decrepit Village.
If Greymon sails into the Grymforge with the party, he can later be found and traded with in the area where deep gnome slaves are digging out Nere. As a follower of the Absolute, he will side with Nere if the party chooses to fight him.