After boarding the boat from the Underdark beach, a boat captained by Corsair Greymon sails up alongside the party's boat. Greymon comes aboard, and the player character has to pass a check to convince him to let the party through to Grymforge. If failing the check, or choosing violence, Greymon attacks and Jerris joins the battle on his side.
Your attack summons thorny vines that possibly Ensnare your target.
Ensnared creatures cannot move and take 1d6Piercing damage at the start of each turn. An ally can use their Help action to try and tear away the vines.