The Library (book 2, episode 10): This adventure is a blast of fantasy, from the Borgesian desert library to the 'sandbenders' who move and dress like the Fremen of Dune. Even more than that incredible power sphere of elements, Aang's insistence on doing so is what finally makes him the Avatar. Sozin's Comet retains its power years later, especially at a time when Americans are openly thinking about what justice means: Should officers of the law have a license to kill in the line of duty? Is it humane to incarcerate people for years? May each of us, when we arrive at our moments of triumph, retain our humanity enough to question the consequences of our actions. Thanks to the long-awaited appearance of the wise Lion Turtle (the ultimate animal hybrid, whose existence was hinted throughout the series), Aang learns that he doesn't have to kill his enemy when a more righteous solution is available: Taking away the power that Ozai used to justify his imperialist slaughter. But only at the end, when he has mastered all four elements, does Aang think about what it would actually mean to 'defeat' the Firelord. For three seasons, Aang has been training to become more powerful than Firelord Ozai. One of the best series finales of all time (certainly in kids' media) wasn't afraid to flip your expectations. Sure, the series finale has a slight advantage in this ranking since it's the length of four separate episodes, but the primary reason Sozin's Comet gets the top spot on this list is because of how perfectly it resolves all the plotlines and character arcs that built up over three seasons.

The way in which the show effortlessly juggles this intense character study that deepens one of its 'villains' with a relatively realistic depiction of the global conflict's consequences is prime of example of how Avatar was more than just a kids' show. He started out the show as an antagonist and here he's forced to confront the consequences of his actions and how people perceive him as he's trying to figure out how he feels about himself. Up until this point, Avatar had done a good job of exploring the horrors of war, but this instance was particularly affecting because the Fire Nation weren't the villains of the story, indicating good and evil aren't as clear cut, and more importantly, we were seeing it through Zuko's eyes. After separating from his uncle, the wayward firebender finds himself in a poor Earth Kingdom village and decides to defend the innocent townspeople from the exploitative Earth Kingdom soldiers.

Avatar goes full Western with this standalone tale about Zuko.

Watch avatar the last airbender book 3 episode 11