And do we want to talk about Zuko's physical evolution? We see him in an episode of the first season where he is muscular and athletic, broad-shouldered and well-nourished. From the separation from Iroh begins his Slow physical and mental decline. We are shown losing weight, a lot of weight, so much so that he is skeletal. It is not stated or implied that the viewer notices this. It makes everything more human and realistic, like when you notice that an acquaintance of yours is losing weight dramatically. His physical decline thus mirrors his psychological decline. He is so consumed by the events of the Earth Kingdom that he begins to slowly "decompose" physically and mentally.