->''"I don't need luck though, I don't want it. I've always had to struggle and fight and that's made me strong. It's made me who I am."''

The SeasonFinale. Zuko struggles to find shelter in the freezing temperatures of the North Pole, while Sokka, Katara and Yue search for him and Aang. At the Northern Water Tribe, firebenders and Fire Nation tanks manage to infiltrate the city. Admiral Zhao slays the moon spirit, Tui, and the waterbenders lose their ability to waterbend. In anger, Aang, who along with Zuko was rescued by Sokka, Katara and Yue, goes into the Avatar State and, in joining with the Ocean Spirit La, destroys the entire Fire Nation armada and army, with the exceptions of Iroh and Zuko. Yue, who was imbued with some of the energy of the Moon Spirit when she was a baby, sacrifices her life to revive it, and becomes the Moon Spirit. Zhao is pulled underwater by the Ocean Spirit in retaliation for slaying the Moon Spirit, refusing to accept Zuko's help when he attempts to save him; Zhao is never seen again. At the end of the episode, Ozai assigns Azula a mission: to hunt down her traitor uncle and brother.
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!!Tropes:

* AscendToAHigherPlaneOfExistence: Yue's connection with the moon allows her to become the moon spirit when the original dies.
* AwakeningTheSleepingGiant: The Ocean and Moon Spirits seemed content to simply swim around in their pond and not actively assist the Water Tribe or oppose the Fire Nation. Iroh warns Zhao about the disastrous consequences of messing with the spirits but Zhao kills the Moon Spirit. The Ocean proceeds to merge with Aang and go on a RoaringRampageOfRevenge against the Fire Nation.
* BadassBoast: What Zhao does to the Moon spirit, Iroh will return tenfold. He doesn't succeed... but only because Zhao ran.
* BerserkButton: Harm to the spirits is one for Iroh.
** Swallowing his pride and accepting his mistakes is a big, fatal one for Zhao - twice. When told not to kill Tui, he lets his anger take control and kills the fish anyway. Later, when he's on the brink of death, his only means of survival is to grasp Zuko's hand - the hand of the kid he hates to the core. Instead of sucking it up, he lets his pride call the shots and lead him straight to a frigid, cold, watery grave.
* BittersweetEnding: The Fire Nation has been repelled and the day is won, but at the cost of Yue's life to Sokka's dismay. Meanwhile, Zuko and Iroh are unaware they've been branded traitors by their nation and a [[HeroKiller much worse threat]] than Zhao is on the horizon.
* BloodlessCarnage: The invasion itself. After Koizilla wipes out the fleet, we never see any dead bodies; considering Zhao's fate, that hints at a rather horrifying possibility for why they're all missing.
** More remarkable is how the enraged Water Spirit is capable of wiping out ''only'' the Fire Nation's troops: the nearby Water tribesmen who bowed down in supplication were spared. We actually see the water pass over them harmlessly.
* CallBack: Hei Bai, the forest spirit in "Winter Solstice: Part 1", returns to aid Aang in the Spirit World.
* CasualDangerDialogue: While Iroh and Zhao are discussing their strategy on their ship, Hahn interrupts, charging at Zhao, who ''casually tosses him overboard'' and resumes the conversation with, "As I was saying..."
** A more frightening variant: Aang talks flatly and casually in front of Koh the entire time he's speaking to him - should he show even a speck of emotion, Koh would steal his face. When Aang suddenly has an epiphany about the koi fish behind Koh's back, it's enough of a realization to make him drop his facade and get a cheerful reaction out of him - and Koh wheels around at the speed of light ready to pounce at Aang's slip-up... only to find Aang has regathered himself and gone dull and emotionless again. To top it all off, Koh taunts him out of spite as he walks away.
* ChekhovsGunman: That girl who appeared in the flashback in "[[Recap/AvatarTheLastAirbenderTheStorm The Storm]]" as well in the opening turns out to be the Firelord's daughter and Zuko's sister. At the end, the firelord sends her to replace Zhao. We still have yet to learn her name, though.
* CityOfCanals: The Northern Water Tribe's city.
* ClaimedByTheSupernatural: Yue's white hair can be a considered a benign example.
* CurbStompBattle: Aang combines with the Ocean Spirit and utterly destroys the Fire Nation fleet. The same goes for Zhao and the Moon Spirit - he's doomed the moment it picks him up in its clutches.
** Also Katara's rematch against Zuko, though she even points out the [[WorfHadtheFlu inequality of the matchup]].
* DeliberatelyMonochrome: While Zhao has the Moon Spirit captive and after he kills it. During the Moonless sequence, the only color comes from firebending and Yue's irises -- in other words, supernatural sources. This tips off Iroh to Yue's true nature.
* DidntThinkThisThrough: Two examples: Zuko's plan was, apparently, "Grab the Avatar and run off into the frozen tundra" (Iroh later calls him on it). Zhao, meanwhile, seems never to have considered any possible consequences to ''destroying the Moon'' apart from "no water bending."
* DreamingOfThingsToCome: Yue's father dreamed about her becoming the Moon spirit and knew that day would come.
* DressingAsTheEnemy: Hahn and his men disguise as Firebender mooks in order to get close to Zhao. It helps that the outfit includes [[FacelessGoons face-obscuring helmets]].
* DrivenToSuicide: Zhao commits suicide by letting the ocean spirit take him after failing to defeat Zuko.
* EveryoneHasStandards: Iroh makes it clear to Zhao that he doesn't believe in killing a spirit to ensure victory for the Fire Nation. Just when Zhao's about to kill it, Iroh sides with Aang on his claim that everyone needs the Moon.
* FaceStealer: Trope Namer. And my, is Koh creepy.
* AGodAmI: Zhao does this after capturing the Moon Spirit. Complete with a MilkingTheGiantCow gesture.
* GodInHumanForm: Zhao learned from a special library that the black and white koi fish in the oasis are actually the Moon and Ocean Spirits. He chose to use this knowledge to destroy the moon, which he believed would cripple the Water Tribe only.
* GodzillaThreshold: The defeat of Zhao's fleet is this to the Fire Nation, as the Fire Lord sends his daughter to drop the hammer.
* HeroicSacrifice: Yue makes one to save the Moon Spirit and her tribe.
* HesDeadJim: When Yue collapses into Sokka's arms, the latter diagnoses her dead after a second of feeling her pulse.
* {{Jerkass}}: The Strange Spirit first encounters in the Spirit World. Rather than help Aang, he tries to shoo him away so that he can meditate in peace. He even voices his relief once Aang leaves, which led to Hei Bai getting angry with him.
* KarmicDeath: Zhao is killed by the Ocean Spirit for (temporarily) slaying the Moon Spirit. Double whammy when you factor in he had a chance to be saved by Zuko and chose to die at La's hands, and so he was subjected to self-inflicted karmic death.
* LastKiss: Between Sokka and Yue before she AscendsToAHigherPlaneOfExistence.
* MeaningfulName: 'Yue' is Chinese for 'moon', which fits how the moon spirit gave energy to save her life as a baby. It becomes all the more fitting when she literally becomes the moon.
* NonchalantDodge: Again, Zhao avoiding Hahn's assassination attempt.
* OhCrap: The appearance of Zuko's sister is a clear sign that Team Avatar is in for trouble, BIGGER trouble.
* OneWingedAngel: [[FanNickname Koizilla]]
** A (more) heroic example: Princess Yue becoming the Moon Spirit.
* PoseOfSupplication: Members of the Waterbender tribe bow down to Kiozilla and are spared while the Firebender troops get washes away.
* RedSkyTakeWarning: While Zhao has the Moon Spirit captive, the moon's light turns red. It's definitely a bad omen.
* TheReveal: That girl from the flashback in "The Storm" who smirked devilishly at Zuko's scarring is none other than his sister. She was smiling out of cruel satisfaction.
* RiddleForTheAges: As far as we know that [[WesternAnimation/TheLegendOfKorra the next Avatar]] is related to the then-current Chief, who would be Chief Arnook's successor since his only child became the Moon?
* RoaringRampageOfRevenge: The Ocean Spirit fuses with Aang and lashes out at the Fire Nation after the Moon Spirit is killed. It does calm down after Yue gives her life to the moon.
* SaveTheVillain: To Sokka's annoyance, Aang won't let Zuko die in the cold. Zuko later attempts to save Zhao from the Ocean Spirit but fails.
* SplashOfColor: From firebending and Yue's irises after the switch to DeliberatelyMonochrome.
* TakeMyHand: Zuko yells this when the Ocean Spirit grabs Zhao. Zhao refuses his enemy's help and lets the spirit drag him underwater.
* TooDumbToLive: Hahn's 'ambush' on Zhao involves getting onto the ship and charging him, loudly declaring his intent to kill him as he runs forward, weapon ready to strike, when his opponent is a powerful bender, has ''another'' powerful bender next to him, and is currently on a ship full of soldiers. Obviously, it doesn't work.
* WhamEpisode: Admiral Zhao dies, Katara is officially a Waterbending master, and the last two minutes of the episode introduce a new and deadly playmate for the crew next season... one Zuko's ''sister''.
* WhamShot: Why hello there, '''Zuko's Sister'''.
* WhatHappenedToTheMouse:
** Hahn's fate after being chucked overboard Zhao's ship is left uncertain. For all we know, he's an ice cube chilling at the bottom of the ocean by now. But after being such a {{Jerkass}} as he is, [[AssholeVictim nobody really gives a rip]].
** Koh mentions that he and Aang will meet again but never comes back in the series. It actually happens in the online game ''VideoGame/EscapeFromTheSpiritWorld''.
* WillOTheWisp: After being transported to the spirit world, Aang runs through a swampy region chasing a mysterious small light sphere. When he climbed up a tree and grabbed it, it made the tree branch dissolve.