Highlandlubber is the 44th episode of the finale season, alongside with "Who Let the Cats Out of the Old Bag's House?"
The episode begins with Captain K'nuckles being given a physical by Dr. Barber. Dr. Barber informs him that he's suffering from "old age". He continues to point out that K'nuckles's sleeping complications and hearing loss are definite signs of old age, then suggests that K'nuckles get the mole on his cheek removed. K'nuckles is downhearted as they leave the doctor's, but Flapjack cheerfully proclaims that they're going to be together forever. K'nuckles tells him that nothing lasts forever, then begins crying, claiming that he's "leaking dreams". In the Candy Barrel, Peppermint Larry gives K'nuckles prune juice, much to his irritation. Suddenly, a fancy-dressed adventurer named Ponce bursts into the Candy Barrel and asks for a flagon of their finest candy. After receiving his candy, he reveals that he's looking for an assistant adventurer.
Everyone immediately crowds around him, begging to be picked. Ponce chooses K'nuckles, claiming that the mole on his cheek is a mark of immortality. The two of them then run off to Ponce's ship to begin their adventure. K'nuckles immediately takes a nap, but his sleep is rudely interrupted when Ponce decides to awaken him by throwing him overboard. K'nuckles screams that he can't swim and is drowning, but Ponce just laughs and claims that immortals can't drown. Flapjack, who followed them, saves K'nuckles. That night, K'nuckles sits up on the crow's nest of the ship as Ponce asks him if he can "feel it" for the hundredth time. A storm rages and K'nuckles is struck by lightning twice. The ship heads straight for the Abyss of Dismal Peril, but Ponce isn't the least bit frightend. Instead, he laughs loudly as he steers the ship directly into the abyss. The ship ends up destroyed, but everyone on board survives.
Ponce offers this to K'nuckles as positive proof that he's immortal and the two head to Treasure Mountain. Meanwhile, Flapjack appears from a barrel with Ponce's pantaloons over his face. He quickly discovers that the pantaloons are from the Stormalong Insane Asylum -- learning this, Flapjack realizes that Ponce must be an escaped mental patient and (presumably) not immortal. At the base of the volcanic mountain, Ponce orders K'nuckles to jump in. When K'nuckles refuses, Ponce demands to know if he wants to be an immortal or not. Flapjack runs up to the volcano with the pantaloons, yelling that Ponce isn't immortal after all. To prove his immortality, Ponce jumps into the volcano. From the volcano, there are strangled cries and lots of coughing.
K'nuckles discovers that his immortality wart was actually just butterscotch. He is saddened, but Flapjack cheers him up by pointing out that they just went on the greatest adventure ever. From the volcano, they hear Ponce laugh and yell, "Can you feeeeel it?" The episode ends here.
Knuckles:But that's my buotey marks