List of Code Lyoko episodes

Milly and Tamiya are doing a report on the school prom. They try to interview Sissi, who was prom queen last year, but she turns them down and makes fun of them for their age. Milly tries to ask Ulrich out, and he turns her down because he's going to the dance with Yumi. Upset, Milly storms off. In her room, she tells Tamiya that she hates everyone, with X.A.N.A. listening from her computer. When Milly tells her teddy bear that she wishes she were bigger and leaves it in the garden shed, X.A.N.A. possesses it and uses it to attack those who make fun of her. It then increases the teddy bear's size to roughly two stories and sets it on the town. Since Ulrich is to protect the school and warn Yumi, it is up to Odd to go to Lyoko and help Aelita deactivate the tower and protect the rest of the town from the rampaging teddy bear. After a return to the past, Milly asks Ulrich to the dance again, and Ulrich complies, embarrassing Sissi.

• This takes place several weeks after "X.A.N.A. Awakens, Part 2"

After Jeremy makes another failed attempt to materialize Aelita, a student named Taelia arrives at school that looks exactly like her. Jeremy is convinced that it must be her, but she seems to have no memory of her experiences with the group. The others are not quite as convinced, but Jeremy insists that the materialization process must have caused her to lose her memory, but the others were right. Aelita is still on Lyoko and captured by a Guardian. Meanwhile, X.A.N.A. possesses the samurai armor that Yumi brought to school and uses it to chase Yumi. Jeremy brings Taelia with him to the factory. Odd and Ulrich must free Aelita and deactivate the tower before Yumi is defeated by the possessed samurai armor and Jeremy is taken away by the police.

Taking a different approach to his research, Jeremy materializes a single hair of Aelita's. Unfortunately, the follow-up test goes awry, and Jeremy has to find out why. Meanwhile, different parts of the school begin to crumble apart. Jeremy learns that his first test damaged Aelita's program, and she'll be deleted if she tries to deactivate a tower. On top of that, they learn that X.A.N.A. is responsible for the damage being caused to the school by using ultrasonic sound waves, which continues to get worse. Jeremy has to fix the damage he caused in time to save Odd, who ends up trapped inside the school with Milly, Tamiya, and Kiwi. Unfortunately, after two tries, both ending in failure, Aelita, with the help of Yumi and Ulrich, has to deactivate the tower or else Odd, Milly, Tamiya, and Kiwi will be killed. After the return to the past, Yumi remembers that Jeremy said that the hair contained Aelita's entire computer code. Jeremy places the hair in the scanner, virtualizes it to Lyoko, and Aelita is inside the tower she deactivated.

This episode takes place one month after the events of the first season. After discovering Aelita's link to the Supercomputer and the inability to shut off the Supercomputer that stems from it, Jeremy works hard to find new and better ways to fight X.A.N.A.. To that end, he develops new vehicles for the group. He also develops a new tower-scanning program that instantly detects activated towers, allowing Aelita to live on Earth. The group encounters a new monster in Lyoko, which Odd names a Tarantula. While adjusting to her new life, the class takes a trip to the nearby woods for a scientific field trip. Ulrich wants to partner up with Yumi, but she's already partnered up with someone named William. He comes from another school, having been expelled from it. During the field trip, Aelita and Jeremy partner up. Jeremy is forced to retrieve his laptop, leaving Aelita in the woods. With him gone, Aelita is frightened by visions of wolves, which lead her to a house known as the Hermitage. There, she has even more visions and is attacked by X.A.N.A.. Once the others arrive to find her, they learn that X.A.N.A. has possessed the house and uses everything in it to attack them. They find Aelita in a sauna in the basement. X.A.N.A. tries to trap them all inside and boil them, but only succeeds in catching Ulrich and Yumi. Aelita and Odd head to the factory to shut down the tower before they are boiled alive.

When Ulrich tries to tell Yumi how he really feels after some prodding by the rest of the group, he finds her talking to William, who is doing the same thing Ulrich had planned to. Yumi turns him down, but Ulrich leaves before hearing it. Meanwhile, X.A.N.A. activates a tower and materializes a Krab. At school, a driving class has been set up to teach the kids road safety. William turns out to be a good driver and Ulrich a rather poor one, which William makes fun of him for. The two then get into a fistfight, much to Yumi's annoyance. William and Ulrich both get detention because of the fight. Jeremy learns of the activated tower shortly after and the group heads to the factory without Ulrich.

In a prequel to "Teddygozilla", twelve-year-old Jeremy discovers a quantum supercomputer in an abandoned factory. Within, he finds that the computer runs a world parallel to Earth, a virtual world called Lyoko, along with an artificial intelligence Jeremy decides to name Maya. Jeremy tries to help Maya as much as he can with understanding what she is doing on Lyoko. With the Supercomputer active, strange events begin to plague Jeremy. He finds new friends he reveals the computer to. Additionally, Ulrich meets the mysterious but beautiful Yumi who beats him in a duel; much to his shock.

• Chronologically, this is the show's two-part 44/46-minute long premiere set a few days before "Teddygozilla"

After another three-week vacation, the group is still looking for a way to fight X.A.N.A.. X.A.N.A., meanwhile, is trying to destroy Lyoko, preventing them from doing just that. He does so by targeting the core, which contains the code that maintains the virtual world. In a side story, Odd blackmails Jim into asking Principal Delmas to make Odd have the same classes as his friends. Additionally, Yumi decides against having a relationship with Ulrich and decides it would be better if they were just friends. While defending the core, Aelita is suddenly devirtualized by the enemy. However, she still ends up back in the scanners and Jeremy realizes that this is because Aelita is fully human, just like the rest of the group, so she does not need Code: Earth anymore to be materialized on Earth.

• Aelita obtains a "weapon" of her own: Deep pink orbs of electrical energy called "energy fields". And along with that newly acquired ability, she can also create a deep pink shield.

In order to compensate for William, who is still under X.A.N.A.'s control, Jeremy sets to work designing brand-new virtual attire and digital "enhanced" weaponry and abilities for his friends and recreating the rest of Lyoko. In order to buy himself time to do this, he activates a tower and uses it to create a clone of his own to attend class in his place. Meanwhile, William's absence is drawing attention, from both the principal and his father. While Jeremy's clone is impressing Jim outside, William appears on Lyoko and tries to put the tower under his master's control. In order to maintain his clone, Jeremy draws more virtual strength from Sector 5 to maintain the activated tower. He eventually runs out of digital energy and the tower is put back under X.A.N.A.'s control. While Odd holds the Jeremy clone off, Aelita, Yumi, and Ulrich go to Lyoko with new outfits and somewhat much stronger abilities and slight improvements of their old weapons. They eventually deactivate the tower. William threatens to push Yumi into the Digital Sea, but before doing so he comes back to his senses. Yumi is saved from the fall by Odd at the last second. Jeremy then initiates a return to the past and creates a William clone to prevent any suspicion about his absence.

• This is the last time Ulrich used his triplicate ability.

Jim's nephew, Chris, the drummer of the Subdigitals, pays a visit to Kadic to look for an opening act for the band's next concert. Everybody tries out, and Aelita turns out to be the one Chris is looking for. However, circumstances make sure that Chris does not realize who Aelita is, and X.A.N.A.'s clone of him only complicates matters, kidnapping Aelita and sending her to Lyoko.

The new virtual, submersible "submarine" (as Jeremy calls it) is almost complete, the last step being a secondary program that needs to be run by 4 PM the next day. However, when Aelita and Jeremy stay up late to set the program up, they are caught and given detention.

The gang manages to convince Jeremy to let them test out the Skid. During this test, the navigation system bugs up, leaving the gang stranded in the digital sea. Jeremy runs to his room to fetch the backup programs, but forgets that it's Fire Safety Day and runs into several teachers, eventually having to scale the roof to get to his room.

When a comet passes near Earth, X.A.N.A. uses a laser-equipped military satellite to split it into chunks, simultaneously aiming the bulk of it directly at the factory. Aelita, Odd, and Ulrich are exploring the digital sea at the time, and X.A.N.A. traps them with a firewall to prevent them from stopping the attack.

Jeremy, Aelita, Ulrich, and Odd go with the rest of their science class on a field trip to an island in the middle of a nearby lake to study water-based plant life. Yumi, not part of the class, remains behind to sit through two important exams. Jeremy's fears about X.A.N.A. attacking at such an inopportune moment are realized when X.A.N.A. creates an electricity-blasting sludge that attacks anyone who approaches the shore. Yumi is forced to go to Lyoko alone. She fights William and during their fight is able to reach his true mind and personality. Though X.A.N.A. soon manages to regain control of William, Yumi is saved by Aelita, who escaped the island on Sissi's bike. Aelita is able to deactivate the tower and Yumi claims that one day they will bring William home. She initiates a return trip to the past and the class is saved from electrocution.

• This episode shows the strong feelings William has for Yumi, since various machines and programs made by Jeremy do not succeed in bringing William back to reality and Yumi's words do.
• The quintet are seen in their original attire for the camping trip.

Jeremy has finally perfected his "teleportation" process, allowing him to send his four best friends to the location of X.A.N.A.'s supercomputer in the real world to destroy it and leave no trace of their heroic activities. He uses it on Aelita and Odd first, sending them to the jungle laboratory containing the supercomputer. As they explore, they find that X.A.N.A. is constructing cybernetic spiders with the help of a team of possessed scientists. Before they can stop him, however, William manages to sever their connection to the real world, bringing them back to Lyoko in the middle of their mission. In a side story, Yumi is angry with Ulrich because he has forgot her fifteenth birthday, so Odd promises to get Yumi a present for him, since Ulrich has detention.

• For some reason, the theme song's scenes are from the first season

When Odd breaks a mirror, a little bad luck follows and jinxes him everywhere, even on Lyoko. A bug in his virtual avatar spreads to Yumi and Aelita, causing annoying pauses and random devirtualization in the Desert Replika. Meanwhile, at the site of the Replika's supercomputer, X.A.N.A. materializes Kankrelats in the real world to stop Ulrich and Yumi. Despite the bug, their mission to destroy X.A.N.A.'s next Replika ends in success, this time by Ulrich, and Odd's luck returns soon afterwards.

• This is the last time Yumi utilizes her one-and-only enhanced special ability of telekinesis in the series.

When Sissi's pen pal from Iceland, Brynja Heringsdötir, arrives at the school, all the boys swoon over her, making Sissi envious. When Brynja takes an interest in Odd, he ends up showing her the Supercomputer. While there, she messes with the computer despite Odd's pleas not to, creating a glitch in a program Jeremy is installing that causes every virtualization to happen in the wrong sector and prevents materialization. This becomes all the more problematic when William catches Aelita alone on Lyoko. When forced to choose between his friends and his new love interest, Odd initially stays with her, but decides that his friends are more important. After rescuing Aelita from William, they make up. As Brynja has not been told anything about the purpose of the Supercomputer, nor does it appear that she even cared in the first place, they have no need to perform a return trip to the past before she leaves.

• This is the last time Aelita utilized her "second sight" ability to detect X.A.N.A.'s pulsations, which she did frequently in the first season.

Jeremy's cousin, Patrick, comes to visit. Jeremy is not entirely happy about it, since Patrick is "super cool" compared to him. Discovering another Replika, Jeremy and his friends plan a mission to destroy it, leaving Sissi alone with Patrick. She is able to convince him to let Herve rummage through Jeremy's computer files. Herve discovers Aelita's forged documents and the program running the Skid, his efforts to decipher it inadvertently draining the Skid's power. To make matters worse, X.A.N.A. possesses both him and Sissi to cause even more damage. Jeremy, meanwhile, deduces that it's his computer back at school causing the damage, and works with Patrick to stop them. Once the attack has passed, Jeremy has Aelita run a return trip to the past to undo the damage caused. The second time around, Jeremy is a bit more appreciative of his cousin, since the two worked well together before. But, unfortunately Patrick goes back to his own school.

• This is the last episode to air on Cartoon Network. The final 7 episodes of the original series were released online.

Aelita finds a photo of herself with Franz Hopper at the Hermitage, with a mathematical equation in the background. Jeremy discovers that the program works as a reset feature to Lyoko, something not too helpful, but useful nonetheless. Meanwhile, Odd, in an attempt to impress a girl in photography class, inadvertently sends the photo to Sissi, who in turn shows it to her father. He questions the group about it, with Jeremy pointing out that Aelita would obviously be 22 by now if she were the one in the photo.

When an embarrassing picture of Yumi is printed in the Kadic newspaper, she turns to Odd as the source. He manages to get Ulrich to take the blame, however, causing tension between him and Yumi. Putting that aside, Jeremy sets up a mission to the next Lyoko copy, an Ice Replika. Its supercomputer is located in Siberia, where X.A.N.A. is growing brains for an unknown purpose. Odd and Yumi are sent to the real world to destroy it, only to be confronted by William. When trying to shut down the tower, Aelita realizes that the data it is generating could be used to free William. After downloading the necessary data and disabling William, everything seems to be set for destroying the Replika. However, X.A.N.A. draws on the power of his many Replikas to create a new monster: the "Kolossus," a massive creature resembling a fire elemental with a sword for a hand.

In order to defeat X.A.N.A., whom they have vastly underestimated, Jeremy plans to design another multi-agent system to combat him. That, however, is still under development. In more immediate matters, Jeremy has figured out how to free William from X.A.N.A., but needs to run his program directly from the Ice Replika's supercomputer. Meanwhile, William's parents visit their son, and the strange behavior of his clone concerns them greatly. Back at the Replika, William and two Mantas come to try to sever the translation. However, the Mantas are quickly destroyed by Yumi and Ulrich. William then jumps into the Digital Void and comes back up with the Kolossus. Jeremy uses some new tricks to stop the Kolossus, allowing Aelita and Odd to reach the supercomputer without worry. However, an army of robotic drones now stationed at the facility complicates matters and they undo Odd's translation. With much effort, Aelita is able to run the program to free William before she is forced back onto Lyoko as well, but their victory comes at a cost: though William is saved, the Skid is destroyed by the Kolossus with Aelita in it. Fortunately, she is devirtualized before the Skidbladnir is totally destroyed. Back on Earth, William is able to take his clone's place, pacifying his concerned parents. Ulrich, meanwhile, has to deal with William's romantic affection for Yumi once more.

• Odd utilizes his purple "shield" ability for the first and final time as a specter on Earth and in the overall series.

With the Skid gone and X.A.N.A.'s replikas at unmanageable numbers, Jeremy continues work on his multi-agent system. Meanwhile, Aelita has nightmares about her father being killed by X.A.N.A.. As Jeremy works, he is contacted by Franz Hopper, who arranges a meeting on Lyoko. William wants to help, but all except Aelita are a little wary of trusting him again. William is left in the lab with Jeremy. After meeting up, Franz transmits the data necessary to finish Jeremy's multi-agent system. However, X.A.N.A. is not willing to give up without a fight, activating a tower to possess William once again while sending the Kolossus to deal with Franz. Yumi willingly devirtualizes herself and fights William while the others protect Franz.

With their mission completed, the group looks back on all their fond memories of Lyoko. Sissi, meanwhile, plants a tracking device on Ulrich in order to discover their secret. When it comes time to shut down the Supercomputer, all but Yumi are unwilling to go through with it: Aelita is still holding onto the hope that her father can somehow be saved, Jeremy does not want to take away the thing which made them friends, and Odd and Ulrich both liked being heroes.