Great quiz! Besides Than and Ying, there were a few other tricky ones like Bosco and Bato (I didn't realize he was in so many episodes!). I was thinking of Teo but couldn't remember his name.
Also, I'm going to be making an Avatar-themed quiz in a few weeks, so if you enjoyed this, please check out my page in the future!
Surprising that Ursa (Zuko and Azula's mother) isn't in more episodes. The flashbacks make such a strong impression that I thought there were more. She only appears in Zuko Alone, The Earth King (briefly in Zuko's dream), and in Sozin's Comet pt. 3 (in Azula's mirror hallucination).
I am also making a quiz, please search "Aang and Korra: 101 Characters." Thank you! I hope to be the first 10-year-old in Jetpunk to have 1,000,000 plays.
Zuko Alone (Zuko considers stealing from them but decides against it when he sees Ying is pregnant.)
Serpent's Pass
The Drill (Team Avatar transport the couple inside the walls before dealing with the drill)
City of Walls and Secrets (Iroh sits next to Ying on the train into the city)
The Awakening
(The couple is seen during the invasion)
Also, apparently Than is in "Tales of Ba Sing Se," though I can't remember when.
Also, I'm going to be making an Avatar-themed quiz in a few weeks, so if you enjoyed this, please check out my page in the future!