After all the bloodshed, betrayals, and reversals of fortune in this season of Black Sails, the season two finale saves the best moments for last in “XVIII.” As the culmination of Captain Flint’s (Toby Stephens) doomed journey to fulfill his dreams nears, as well as the outcome of Captain Vane’s (Zach McGowan) dangerous rescue mission, “XVIII” provides closure to several major story lines while kicking the door open to new ones with some significant cliffhangers.