|"We'll have to attack in a swarm to try to keep you guys safe in the hummingbird suits. It looks like they're our only hope."|
|— Korra to Team Avatar.|
"Day of the Colossus" is the twelfth and penultimate episode of Book Four: Balance of The Legend of Korra and the 51st of the overall series. It was released along with "The Last Stand" on Nick.com and through the Nick app on December 19, 2014, and aired on Nicktoons the same night.
Team Avatar escapes from the rubble of the Future Industries factory and devises a plan to take down Kuvira's giant mecha suit. The benders try to slow the suit down, but its power overwhelms them. Varrick tries to use an electromagnetic pulse to short-circuit the giant mecha but fails, only disabling a battalion of much smaller mecha suits instead. Hiroshi Sato is temporarily released from prison to aid Asami, Varrick, and Zhu Li in re-purposing the hummingbird suits for combat use. While working on the suits, Hiroshi and Asami bury the hatchet, and Varrick successfully proposes to Zhu Li. Baatar Jr. reveals a way to disable the giant mecha, and the team uses it to create a plan aimed at infiltrating the suit itself. Using a plasma saw rigged to the hummingbird suit, Hiroshi and Asami successfully cut a hole in a leg of Kuvira's mecha suit. Seconds before Kuvira crushes their suit, Hiroshi ejects Asami from it, saving her life and sacrificing his own to finish cutting the hole, and Korra, Mako, Bolin, Lin, and Suyin manage to enter the mecha through the hole.
Kuvira's attempt to kill Team Avatar, their allies, and Baatar Jr. by destroying the Future Industries warehouse in which they were sheltering is foiled by Bolin, who has earthbent a heavy wall on top of all of them, protecting them from the collapsing building. After the dust clears, he raises it long enough for the entire group to escape. Tenzin flies to a rooftop and sees that Kuvira's giant mecha suit is crossing a bridge toward their position, along with a platoon of smaller ones; he quickly flies back to inform the group. Bolin, telling the group that they lack the strength to match Kuvira, suggests allowing Kuvira to conquer the city for now, which would give the team time to develop a strategy for defeating her. Mako counters that other citizens have yet to be evacuated, and that, if Kuvira sees Wu among them, she might fire her spirit energy cannon at him, wiping out large numbers of civilians. Korra refuses to abandon the city, upset that she could not stop Kuvira from taking Zaofu and unwilling to allow it to happen again; she insists that Kuvira is a threat to the entire world, a statement supported by Lin, who promptly arrives on the scene. They decide to confront Kuvira head-on; although Varrick grimly points out that all the hummingbird mecha suits have been destroyed, Asami notes that a few of the prototypes are at her office, and capable of offering air support. Korra tells Suyin to take the wounded to Asami's office while she, Team Avatar, the Air Nation, Lin, Wei, and Wing try again to take down Kuvira's mecha.
At Central City Station, Pema encourages an unnerved crowd to remain calm, assuring them that new trains will be on their way. However, a conductor arrives and informs everyone that the tracks have been dismantled by Kuvira's forces, while Tu tells everyone that Kuvira's army is coming closer. The people start to panic, but Wu manages to ease the tension; he informs them that he has a strategy in mind and takes Tu with him to find help, asking Pema to preside over the unruly crowd in the meantime.
On the streets of Republic City, Team Avatar is racing to meet the giant mecha when Meelo, noticing a paint store, invents a strategy for stopping the machine using paint and balloons. Acting upon the idea, the airbenders, each armed with several paint-filled balloons, fly toward the mecha suit as it marches through the city. Kuvira promptly targets and fires her spirit weapon at them; however, most of the airbenders avoid the blast and continue their advance, save for Kai and Ryu, the former helping the latter recover from the blast. The remaining airbenders fly around the giant's head; Kuvira attempts to swat them with the mecha suit's arms as Meelo and the others throw the paint balloons at the mecha suit's target crosshairs and the windows of its control room, obstructing Kuvira's view. While Kuvira activates the machine's water jets to clear the paint, Lin tries to metalbend one of the mecha suit's feet and fails, discovering that the joints are also made of platinum. Bolin lavabends the earth beneath the foot, while Wei and Wing entangle the legs with two spools of metal cable. With the mecha becoming unbalanced, Korra and the airbenders attempt to topple the giant using a combined airbending attack, but Kuvira fires a blast at them, injuring several airbenders in the process and forcing Team Avatar to retreat and Lin to seek aid.
At Asami's office, Varrick, Zhu Li, and Asami try to fix and test the hummingbird mecha suits, with no success. Daw warns them about Kuvira's advancing troops, and Varrick comes up with an idea of his own on how to stop Kuvira's mecha suit. He instructs Asami to disconnect anything electrical and asks Zhu Li to come with him.
At the factory's upper floor, Baatar Jr. wakes up, confused by his unfamiliar surroundings. Suyin, who is with him, suggests that he rest, and Baatar Jr., apologizing for betraying his family, asks her why Kuvira fired her weapon at him as he gave his life to her. All Suyin can say to him is that Kuvira is "a complicated person." Baatar Jr. worries that Wei, Wing, and Opal will never forgive him, but Suyin assures him that time will mend their relationship, saying they will work through it as a family.
At a metal tower on the factory's rooftop, Zhu Li asks Varrick if he is sure of his plan, and Varrick, working on some wires, responds that he is; he reasons that, since he stopped a number of mecha suits with an electromagnetic pulse before, he can use a "giant" one to stop a "giant" suit. After a short pause, Varrick switches gears, telling Zhu Li that he has been thinking about something; when Zhu Li tells him that he is always thinking, Varrick clarifies that he has been thinking about her specifically, and that, given their current, hazardous situation, he feels he needs to tell her some things. He then begins telling her about an ostrich horse named "Mrs. Beaks", which he had for a pet when he was a child; she is somewhat disappointed by the turn in the conversation, but he continues, saying that, while he loved Mrs. Beaks, he never truly valued the animal as he should have. Before he can go any further, Zhu Li, interrupting him, informs him that Kuvira's troops are in range and activates the pulse; the energy field causes the platoon of smaller mecha suits to be disabled, but Kuvira's giant continues to advance untouched. Panicked, Varrick tells her to "do the thing" again, but Zhu Li sadly expresses that "there are no more things to do".
In the cockpit of the mecha giant, Kuvira demands to know what happened to her first two mecha platoons, prompting one of her soldiers to inform her of the electromagnetic pulse. She is informed that while the suit is still capable of movement, the energy weapon is temporarily down. Presuming that Varrick is behind the attack, she orders the soldier to locate the source of the pulse and commands the remaining mecha platoons to continue their sweep of the city and capture anyone they find.
Back at Future Industries Tower, Bolin inquires why the small mecha suits, rather than the big one, were disabled by Varrick's electromagnetic pulse. Baatar Jr. explains that it is powered by spirit vine energy instead of regular electricity, and sadly concludes that it is unstoppable. Much to everyone's surprise, his statement is contradicted by Hiroshi, who has entered the room with Lin. Seeing everyone's shock, Lin explains that she freed the genius engineer from prison, enlisting his help to find a way to stop Kuvira. Hiroshi tells the group that he understands the animosity they feel toward him, but insists that he loves Republic City and is willing to risk everything to protect it. A skeptical Korra asks him if he knows how to defeat the enormous mecha, and Hiroshi draws a comparison to a virus, stating that they must breach the skin of the mecha and shut it down from the inside. When Korra wonders how such a feat is possible, he muses that they could use the plasma saws Future Industries uses to cut platinum; when Asami notes that the saws are too heavy and bulky to be carried by their small hummingbird suits, he adapts his plan, opting to add an electrical element to the suits' pre-existing welding torches and convert them into plasma saws. Varrick warns that being the equivalent of a metal mosquito carries a high risk of being swatted, prompting Korra to decide that they should attack Kuvira's suit as a group, drawing her attention away from the hummingbird mecha suits, who would use the distraction to cut a hole in the platinum armor unnoticed.
At the train station, Pema sings an old airbender song in an attempt to amuse the evacuees, but she only manages to get them bored. As she suggests they play the button game, Wu and Tu arrive on the backs of two badgermoles; a stunned Pema asks them where they found the badgermoles, and Wu happily explains they are the zoo. He explains that they can use the large, digging animals to tunnel out of the city without Kuvira noticing, as they are powerful earthbenders and, unlike Mako, have always loved Wu's singing. One of the refugees is skeptical about the idea but quickly calls to follow the badgermoles after another building near the station is obliterated by the spirit cannon. As Wu begins to sing, the badgermoles earthbend a hole in the floor between the rails.
Inside the giant mecha, Kuvira orders the mecha platoons to report their findings; the third platoon answers that they have found no one, and the fourth platoon answers that they are nearing the train station. One of the cockpit operators informs Kuvira they have pinpointed Future Industries Tower as the source of the electromagnetic pulse, and she turns, piloting the mecha in the tower's direction. Meanwhile, in Asami's office, Daw alerts the others to Kuvira's advance, and Korra asks Asami how much more time finishing the plasma saws will take. After Asami assures her that they are almost done, Baatar Jr. advises Korra to find the mecha's engine room, and reveals a way to defeat the machine: simultaneously shutting off the room's two emergency shutoff levers. Korra thanks him and tells the others to follow her, planning to stall for time by impeding the mecha's progress.
They confront the mecha on the streets nearby; Kuvira unleashes a spirit beam on Korra, who avoids the attack in midair and assaults the machine with earthbending. Her attacks continue as Kuvira tries to fire the weapon again, but the airbenders push the its barrel downward, directing the beam into the street below; the blast throws the mecha off balance, leaning it against a building. Kuvira, staggered, watches from the cockpit as, among the airbenders flying around the giant, Meelo slams against a window, looking through the glass at her. Kuvira tries to squash him with an arm of the mecha, but Meelo flies away, resulting in the mecha suit hitting itself. Kuvira fires on Meelo as he flies; while he avoids the attack, the beam comes close to striking Jinora. Tenzin intercepts Jinora in midair, saving her from a direct impact, but the blast knocks both of them unconscious. Ikki and Meelo dive to catch them as they fall; Ikki catches Jinora, and Meelo, struggling to break the fall of the much heavier Tenzin, manages to airbend with his feet, softening the impact with the hard ground. Bolin, Lin and Suyin slice a building and throw it against the mecha in an attempt to pin it down, but the mecha rights itself again, renewing the team's despair.
In the tunnel created by the badgermoles, Wu, still singing, is on a song thanking Yin for her help and kindness; while she looks on in admiration, the other refugees sport expressions of confusion and disbelief, several of them even covering their ears in an attempt to block out the royal's singing. The song is interrupted, however, when three mecha suits suddenly ambush their group. The Earth Empire sergeant orders them to surrender, as they are now Earth Kingdom prisoners, and adds that Wu needs to stop singing. Wu, in turn, tells him not to harm the innocent civilians with him, asking them to take him to Kuvira, with whom he has business to discuss. Tu tries to change his mind, but Wu insists and begins singing a song to Kuvira's soldiers, relaying to them his trust in his badgermoles, which promptly disappear into the darkness. As the Earth Empire sergeant starts to mock him, claiming his badgermoles have deserted him due to his "terrible singing", the badgermoles reappear and crush their mecha suits; a delighted Wu sings them a song to thank them.
At Asami's office, as Hiroshi cuts a piece of platinum using a plasma saw, Asami tells him that, if they stop the mecha suit, it will be because of his efforts. Hiroshi reminds her that she designed the suits, and that he has enjoyed working with his daughter, and the two finally reconcile with each other. Meanwhile, as they prepare to climb into the suits, Varrick tells Zhu Li he needs to attach something before they go; removing a ring from his pocket, he asks her if she will "do the thing" for the rest of their lives, and Zhu Li, thrilled, answers with a wholehearted yes. An ecstatic Varrick kisses Zhu Li, declaring that the time has come to "attach [their] barely functional rust buckets to a giant killer smashing machine".
The hummingbird suits, one piloted by Varrick and Zhu Li and the other by Asami and Hiroshi, join the fray around the mecha as the Beifongs and the airbenders try in vain to slow it down. As the hummingbird suits approach, Kuvira fires the cannon at them, but they avoid its attack easily; Varrick and Zhu Li land on its back, thinking it to be the mecha's blind spot, but it swivels around and nearly smashes them. Korra intervenes, bending water from a nearby river to freeze the mecha suit's body and left hand; with its free hand, Kuvira fires a spirit beam against Varrick and Zhu Li's hummingbird suit, damaging one of its wings and forcing them to eject as it plummets downward. Korra freezes its right hand, immobilizing the cannon, which gives Asami and Hiroshi the chance to approach it. They attack the suit to the mecha, and Hiroshi starts to cut a hole with a plasma saw; Kuvira, yelling at her cockpit crew, demands that they increase the power output to the mecha suit in order to free it. Asami notices the mecha's hand slowly cracking the ice around it, but when she tries to tell Hiroshi they should leave, he refuses, insisting he is close to finishing. Kuvira quickly frees the suit's hand; she brings it down on the hummingbird suit with crushing force, killing Hiroshi, but not before he ejects Asami from the suit, telling his daughter he loves her. As Asami, dangling from her parachute, watches, the mangled remains of the suit fall away, revealing the result of Hiroshi's sacrifice: a perfect breach in the skin of the towering mecha.
Korra, Mako, Bolin, Lin, and Suyin immediately dash toward the breach. Kuvira tries to crush them as well, but Korra blocks the arm's swing with a massive block of ice. Kuvira's final, desperate attempt to defend against them crashes down onto the breach too late: Team Avatar has successfully infiltrated the mecha.
- Janet Varney - Korra
- David Faustino - Mako
- P.J. Byrne - Bolin
- Seychelle Gabriel - Asami
- J.K. Simmons - Tenzin
- Zelda Williams - Kuvira
- John Michael Higgins - Varrick
- Mindy Sterling - Beifong
- Logan Wells - Meelo
- Jeff Bennett - Radio broadcaster
- Stephanie Sheh - Zhu Li
- Anne Heche - Su
- Sunil Malhotra - Wu
- Todd Haberkorn - Baatar Jr
- Maria Bamford - Pema
- Greg Cipes - Tu
- Dee Bradley Baker
- Jim Meskimen
- Daniel Dae Kim - Hiroshi
- Main article: Transcript:Day of the Colossus
- Main article: Writing in the World of Avatar
- The Future Industries advertisement billboard was previously present as a magazine advertisement in "Reunion".
- Varrick recalls his use of an electromagnetic pulse to disable mecha suits in "Reunion".
- Badgermoles' love of music was last used to dig tunnels in "The Cave of Two Lovers".
- Hiroshi's suggestion of taking out Kuvira's enormous mecha suit from the inside is similar to Sokka's idea of taking out the Fire Nation drill from inside in "The Drill".
- Varrick was raised on a farm, where he had an ostrich horse named Mrs. Beaks.
- Varrick spent time with a circus.
- Zhu Li's last name is Moon.
- During the airbenders' assault on Kuvira's mecha suit, the view from inside the control room shows that all the front windows are completely covered in paint. In the next scene before the windows are cleared, they are covered in less paint, especially around the edges.
- After Kuvira forces the airbenders to stop their attack on her enormous mecha suit, Jinora is seen tending to her father, while Kai is checking up on Ikki in the background. When the shot changes from an overview to a back-view, it is suddenly Ikki who is standing next to Tenzin, and Kai and Jinora have disappeared. When the shot changes again to a side-view, Jinora is back tending to her father.
- The Air Acolyte woman is shown to be part of the group of evacuees at Central City Station, though she is not seen again when the group moves underground.
- When the badgermoles crush the three mecha suits, their tails are covered with brown fur like the rest of their bodies, whereas they are normally fur-less and a soft pink color.
- This episode, along with "The Last Stand", make up the only two episodes in Book Four to be released together as an hour long special.
- The building on which the airbenders perch to overbalance the mecha suit with their airbending bears similarities to the Flatiron Building in New York City.
- This is Meelo's last speaking role in the series.