|[List of appearances]|
Krux was one of the two Elemental Masters of Time that had the ability to reverse and pause the flow of time. He and his twin Acronix helped the fight against the Serpentine in the Serpentine Wars. After the war was won, Krux and his twin believed they held the most powerful element and thought they deserved to rule. They turned against the Elemental Alliance and together managed to overpower them. In a last effort, Wu recruited Ray and Maya to forge blades made of Chronosteel, which have the ability to absorb elemental energy. After a lengthy battle, Wu and Garmadon successfully strip Acronix and Krux of their powers and store them in the blades. Wu and Garmadon knew the blades were too powerful so they created a time vortex and threw them into it, so they would be lost to the ages. However, Krux and Acronix refused to admit defeat and jumped in after them. Acronix flew through the vortex to land in Ninjago 40 years later. Krux, however, decided to jump out of the vortex and formulate a plan. Unbeknownst to him, the Reversal Time Blade fell out with him. Until his brother returned from the vortex, he disguised himself as a museum curator named Dr. Sander Saunders. Under this guise, he was able to hide from Wu and develop a plan to one day rule Ninjago when his brother returns.
He started working with eggs from the Great Devourer in order to harness the mighty snake's offspring; the Vermillion. In forming his plan, he knew he needed blacksmiths. He made efforts to befriend Ray and Maya, the very blacksmiths that forged the blades that defeated him and his brother. After some time, he revealed himself to the Blacksmiths as one of the Time Twins and threatened to harm their children, Kai and Nya, if they didn't come with him to help him with his plan. He set them up in a Blacksmith Forge in a swamp not far off the outskirts of the city. There they forged armour and the shell of a time machine known as the Iron Doom.
Under his guise of Dr. Saunders, he gave museum tours for school groups, which Cole rather enjoyed as a child, and setting up exhibits. On one Day of the Departed, forty years later, he opened an exhibit called the Hall of Villainy, which contained mannequins of the villains of the past that have taken on the ninja. As a result of Yang tricking Cole, the ghosts of said villains returned from the Departed Realm and possessed their respective statues. The ghosts took their mannequins to take on the ninja that put them in the Departed Realm. The ninja were successful in defeating the ghosts, but the result was many damaged statues from the Hall. As a sign of apology, the ninja agreed to help Dr. Saunders put them back together and clean up the museum. While cleaning, Cole discovers a large mural depicting a battle that none of the ninja are familiar with. Saunders tells them it was a made up story about Wu and Garmadon taking on two twins that had the power to manipulate time. At the same time, Acronix has returned from the Time Vortex and Wu has met him to finish the battle he started forty years ago. After the ninja go to the Monastery to fight Acronix, they believe he perished in the wildfire that ensues. Unbeknownst to them, he had escaped to the museum to meet up with his brother who finally takes off his disguise.
Krux informs Acronix of what he has been working on for the last forty years. Acronix becomes distracted by all of the modern technology he missed out on, Krux reveals he detests modern living, believing everyone to be distracted like infants. Krux shows Acronix the Vermillion he had been breeding and uses them to kidnap Cyrus Borg for the purpose of building a time machine to go into the Iron Doom shell.
In moving forward with the plan, Acronix grows concerned about the success of the plan, wondering how they will control all the Vermillion warriors. Krux assures him he had 40 years to think of this plan and introduces him to Commander Machia, Commander Blunck and Commander Raggmunk, whom are bred to be tactical leaders and to be able to control the Vermillion via a hive mind. When Kai arrives to the museum to ask Dr. Saunders about the Vermillion helmet, Acronix is keen to destroy him, but Krux doesn't want to draw that kind of attention in a public place. Krux goes out in his Dr. Saunders disguise, trying to coax Kai out of the museum. Krux's identity is revealed to Kai after he trips and his disguise is pulled off. A fight ensues which Acronix soon joins, but Nya arrives to assist her brother against the Time Twins. Acronix concedes that they are good, but Krux assures that they are better. When Krux is locked in a sarcophagus, Acronix uses the Forward Time Blade to escape with his brother and Cyrus Borg.
After eluding Kai and Nya, the Time Twins set up in their new base located in a swamp. Krux orders Machia to torture Borg into building their time apparatus, so they can use the Time Blades' power to travel anywhere in time. Acronix takes a liking to her methods and Krux teases him for having a crush on Machia, just before the Slow-Mo Time Blade arrives and slows time in Ninjago. Acronix uses his BorgWatch to locate where it landed, much to Krux's disdain. Machia sees it has landed in the Eastern Sea of Sand and sends Blunck and Raggmunk to retrieve it. They are however unsuccessful and the Time Twins scold the snake generals for their failure and for using the Time Blade. Machia plans an attack on the Airjitzu Temple in order to take the blade back from the ninja. When all Machia's plans to retrieve the blade were foiled by the ninja, Krux and Acronix arrived at the temple to take on the ninja themselves. Despite Acronix being slowed by a rapidly aging Wu, and Krux being defeated by Lloyd, they are still able to retrieve the Time Blade and capture Wu, thanks to Machia. Acronix and Krux promote her to Supreme Commander for these actions.
With both Time Blades, their time apparatus nearing completion and Wu in their hands, the Time Twins have the upper hand. When the Pause Time Blade arrives, Krux, Acronix and Machia take Borg with them to retrieve it. Unbeknownst to them, the ninja are infiltrating their swamp base to find Wu, Borg and the citizens held captive, as well as whatever they are building. Kai and Nya, however, have found their parents, who have been held captive by Krux for many years. When Ray reveals that the Reversal Blade had been hidden in the Boiling Sea, a place only Masters of Fire and Water can access, Krux and Acronix enter demanding Kai and Nya retrieve it for them. They convince them by threatening their parents and telling them it's the only way to save Wu. Once the Blade was retrieved, Acronix revealed they were lying and fought the two for the Blade. In the fight, Acronix hits Ray with the same punch he hit Wu with at the Monastery. Krux fights Kai for the Reversal Blade, but he uses it against the Time Twin. Using the Pause Blade, the Twins are eventually successful in taking the final Time Blade and leaves the heroes behind. They plug the Time Blades into the apparatus, which is now connected to the Iron Doom mech. They create a Time Vortex to travel back to the moment they lost to the Elemental Masters 40 years prior with their Vermillion army. Little do Krux and Acronix know, Kai, Nya and Wu follow them through the time vortex aboard the Fusion Dragon.
Acronix and Krux arrive moments after they disappeared through the vortex and launch an attack on the Elemental Masters. Having no idea how to defeat the Vermillion soldiers, the Elemental Alliance is quickly overwhelmed. Kai and Nya, posing as their parents, assist them and manage to push the Vermillion back. Growing tired of waiting for victory, Acronix and Krux smash Machia , Blunck and Raggmunk back to their component snakes and take control of the army themselves, using Blunck and Raggmunk's helmets. They order all the snakes back to the Iron Doom to bring it to life and the Time Twins use it to destroy the Elemental Masters instead. They eventually force Wu from the past to yeild at the expense of the destruction of the Elemental Alliance. But Kai and Nya don't stop fighting back and use the Fusion Dragon to attack the mech while the Elemental Masters used their powers on it. Acronix complains that Ray and Maya are as troublesome as their children, before Krux realises they are their children and Kai and Nya followed them somehow. The Fusion Dragon is eventually successful in disarming the Iron Doom, which aggravates Krux, but Acronix reminds they can go anywhere in time and suggests travelling forward to a time where Kai and Nya won't exist. The Iron Doom creates another Vortex and disappears into Time, leaving Kai and Nya behind. But Nya had retrieved the Reversal Blade from the past that fell from the Vortex and healed Wu. The three used the Time Blade to reverse back to before the Iron Doom disappeared and manage to smuggle themselves aboard. Acronix explains to his brother that going forward into the future means no one will recognise them, until Kai, Nya and Wu make their presence known. A final battle ensues, but during the battle, Wu looks out into the Vortex and sees that Ray is rapidly aging. Thinking quick, he rips the Reversal Blade out of the Time Apparatus, sending the Iron Doom haywire. He gives the Blade to Kai and Nya, who he pushes from the Iron Doom and back into the present. Wu then confronts the twins, continuing the fight as the Iron Doom is lost in time.
- Though the 70626 Dawn of Iron Doom box incorrectly identifies Krux's minifigure as "Acronix".
- Krux's old minifigure has a double sided face, the other depicting Dr. Saunders.
Gallery of variants