"The point is, it's only a matter of time until Dodo Head's plan crashes down around his ears. Which only makes it more dangerous from the perspective of Team Azula," Usani said. "You see, when the wheels fall off, the first casualty is going to be Sokka."
Butt Monkey: No one likes the Northern Water Tribe. Not even the Southern Water Tribe. Also, Doro Kim gets zero respect—even Long Feng thinks he's an idiot. Oh, and he has an in-universe detractor nickname (see above). Yeah.
Chekhov's Gun: A couple of the info dumps have turned out to have contained information useful to the story later. (Some planned, some not.)
Chekhov's Gunman: On a date with Sokka, Azula mentions that her father got banished from the Fire Nation for attempting a coup. Guess who shows up in the very next chapter?
Combat Pragmatist: Would Azula snipe airbenders with lightning before they've gotten close enough to counter-attack? Would Sokka hit Ozai in the temple with his boomerang while he was distracted giving a villainous speech to Azula? The answer to both questions is yes.
Daddy's Little Villain: Tsubasa, though it would be better to say Mommy's little villain. Also, to a lesser extent, Hahn.
The Dark Arts: There's a certain airbending discipline called voidbending and/or domination-airbending which is specifically called "a dark side to our art", but doesn't seem so bad...until later...
For Want of a Nail: Instead of wreaking Sozin's throneroom when he discovers the Earth Kingdom colony, Avatar Roku has a nice, civilized debate about it.
Good Is Not Nice: Aside from Azula being one of the good guys in this universe, there's Mai, and Tsubasa before she's revealed to be The Mole and after her Heel-Face Turn, not to mention Kasha and Usani.
Gambit Roulette: A running gag is someone pointing out how OC Doro Kim's plans could never possibly work
Heel Realization: Tsubasa, after realizing that her precious voidbending was forbidden for a reason.
Immortality: Ilmarinen is more-or-less type one, but it's temporary, lasting for "only" a thousand years, and then he dies for real...and it's been just about a thousand years. He's grooming Piandao to take his place.
Karma Houdini: Wakaun and later Kazane both escape being punished for their crimes, in spite of the fact that they were responsible for the kidnapping and attempted murder of Sokka and the Avatar, respectively.
Sliding Scale of Villain Threat: Wakaun wanted to kill Sokka (Doro Kim wanted to start a war, but whatever), Kazane wanted to kill the Avatar, Zhou wanted to become immortal (and, presumably, take over the world).
Unholy Holy Sword: Airbending, of all things! Well, to be more precise, certain airbenders can (temporarily) increase their power by sucking out a person or animal's soul! The truly scary thing is, they don't even know that they're doing it.
Worf Had The Flu: The freaking Avatar was the next best thing to useless in the biggest fight scene to date because she'd just been held captive and immobile for several days and could barely stand. And the reason Ozai was defeated by Sokka, of all people? A lucky-shot sucker blow to the temple with his boomerang while he was distracted giving a villain-like speech.
World Building: The whole point of the exercise is to explore the Avatar universe in greater detail... giving us things like airbender supremacists, slavers, criminal undergrounds, even Eldritch Abominations!
Yuri Fan: There's some evidence that author S-Michael is one of these.