Filler episodes tend to get a bad rep because they do nothing but, well, literally fill up a series' runtime. But Avatar: The Last Airbender uses its filler episodes extraordinarily well. With the pressure on Aang to master all four elements and the fate of the world resting on his shoulders, it's overwhelming for our protagonist but can also be overwhelming for the audience. The show's filler episodes provide a nice break from all of the action and plot-heavy episodes.
Though usually used for purely comedic or entertainment purposes, The Last Airbender's filler episodes still integrate character development or important context to the overall plot that make the viewing experience all the more enriching.
A Seldom Heard Voice
Appa is one of the most lovable creatures in the series (aside from maybe Momo). We also know how much the Gaang relies on him -- especially Aang, who thinks of the sky bison as his best friend and part of his family. That’s why, when Appa gets captured by the sandbenders and Aang enters the Avatar mode from rage, it’s a moment that we can wholeheartedly empathize with.
This makes “Appa’s Lost Days” one of the most heartbreaking episodes in Book Two; revealing what Appa endured during his time away from Aang. After Appa gets captured by the sandbenders, he gets traded to a Fire Nation circus where he’s subjected to mistreatment and humiliation. Even after his escape, his suffering doesn’t stop: he gets attacked by a Boarcupine and then by Azula.
The show doesn't normally focus on characters who aren’t a protagonist, so to have the series dedicate one episode to a character who isn’t even human gives us a unique perspective on the world of Avatar. This episode even won a Humane Society Genesis Award for its depiction of animal cruelty.
Everyone's Day Off
The Gaang separate and have a day all to themselves in "Tales of Ba Sing Se." Katara and Toph bond on a girl's day out; Aang helps with a neglected zoo; Sokka ends up in a poetry class and Zuko tastes the life he could have if he kept his true identity under wraps and lived in Ba Sing Se as a refugee.
The most touching and memorable tale, however, is Iroh's. Up until this point, Iroh's portrayed as the kind, comical uncle who provides sage advice. True to form, he helps some villagers get out of sticky situations in this episode. But it's here that we also catch a glimpse of Iroh's hidden pain as he sings "Leaves from the Vine" to his son's grave on his birthday. The song is especially sad when you realize it's about a soldier returning home, which Iroh's son never got the chance to.
Parody and Propaganda
Just before our heroes face-off against Fire Lord Ozai in what promises to be an epic battle, we get a little refresher in the form of a play, called "The Boy in the Iceberg." Featured in “The Ember Island Players” episode, this origin story for Aang has some key differences to what we and the Gang know to be true. For instance, Aang’s played by a girl and Toph is played by an enormous, muscular man (that she’s completely happy with).
The play pokes fun at some of the characters’ key traits, like Katara’s tendency for rambling speeches about hope, Zuko’s obsession with getting his honor back and Sokka’s love of food. The show also uses it to comment on its own failures, like when Sokka remarks that Jet’s death was unclear.
But more than just a hilariously inaccurate summary of what has happened since Book One, “The Ember Island Players” is fraught with Fire Nation propaganda. It ends with the audience celebrating Fire Lord Ozai defeating the Avatar even though it hasn't even happened yet, a chilling reminder of the real threat still looming large.
Being Vulnerable
"The Beach" is the first time that we see Zuko, Azula, Ty Lee and Mai, who have been forced to grow up fast due to the war, are finally able to act like teenagers -- vacationing on a beach and later crashing (and destroying) a party. It's also the first and only time that we see the four Fire Nation characters bond.
As well as slipping into their bathing suits, they all seem to shed their emotional armor, too. Ty Lee fears losing her identity and becoming part of a matching set; Mai had to suppress her emotions to please her parents and, in a rare show of vulnerability, Azula confesses that her mother thought she was a monster and admits it hurt to hear it. Most importantly, Zuko explodes in frustration and anger because he's confused about his purpose in life, forcing him to confront his previous ideas of right and wrong.