Assassin’s Creed IV: Black Flag did a lot for the series. By expanding on the ocean combat of AC3 and making it central to the games’ premise, it reinvigorated a franchise that had become increasingly rote. On top of this, it also allowed for the introduction of the best collectibles of the series to date.
Most game collectibles take the form of random objects scattered around the world (diary entries, feathers, hidden packages), usually providing an experience bonus or easter egg once a certain amount have been collected. Others unlock concept art or expand on the games’ lore. The inclusion of these in any game can be a mixed bag, and Assassin’s Creed has fallen afoul of an excess of them in the past, drawing criticism for what could be deemed as unnecessary padding. Indeed, Black Flag had its share of extraneous collectibles of varying usefulness (I still haven’t collected the 200 animus fragments), but among these were the uniquely memorable sea shanties.