|[List of appearances]|
Acronix was one of the Elemental Masters of Time, the other being Krux, his twin. Acronix had the power to fast-forward and slow down time. The two masters aided the Elemental Alliance in their effort in the Serpentine Wars. Once the war was over, the two Time Twins thought they held the most powerful element and turned against the alliance in an effort to rule Ninjago. The Time Twins were right and the entire Alliance could not defeat the rogue Masters. Wu, Ray and Maya formulated a plan to forge four blades out of chronosteel; a metal that is special being able to absorb elemental energy. Wu and Garmadon fought the twins until using the blades on them and stripping them of their powers. The Time Twins were easily subdued by the other Elemental Masters and Wu and Garmadon created a temporal vortex with the blades so they would be lost to time. Acronix and Krux couldn't stand to lose, so they jumped into the vortex after them. However, Krux jumped out of the vortex, unbeknownst to him the Reversal Time Blade fell out with him.
Acronix exited the vortex 40 years after jumping in. However, having traveled through time, it only feels like seconds to him. To his surprise, Wu had seen something in the time vortex that hinted at when Acronix would return. Wu, now an old man, is waiting for him to finish the fight, to which Acronix agrees. His arrogance gets the better of him and, after a while, Wu has him hanging from the Monastery roof. Acronix reluctantly yields but just as Wu announces the time the battle finished, the Forward Time Blade arrives and sends all of Ninjago one minute forward. Acronix, now on equal ground to Wu, starts the battle again, now with the power to jump forward in time. The battle grows harder for Wu and he is eventually struck by the blade and greatly weakened. In one final attempt to defeat him Wu uses Spinjitzu against Acronix, but only ends up hanging precariously from the cliff side. The ninja arrive just in time to take on Acronix, however his Time Blade makes him a formidable foe for the team. However, rogue flames from Kai's power began to engulf the Monastery and the ninja believe Acronix fell victim to the fire. In actual fact, he had used the Time Blade to escape. He travels to the Museum to meet curator Dr. Saunders, who turns out to be his brother Krux.
Acronix regroups with Krux and is brought up to speed on what Krux had been working on for the last 40 years, which was breeding an army of snake warriors known as the Vermillion. Acronix is quick to take a fancy to all the technology that appeared in Ninjago in his absence, especially the BorgPad. Krux, however, despises everything about modern life and informs Acronix of his plan to retun Ninjago to its "pre-modern glory". The Twin Twins used the first Vermillion warriors to capture Cyrus Borg. In the process, Acronix uses his fast-forward abilities to knock Zane out of action.
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. When Krux's identity is revealed to Kai, 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. Using the Pause Blade, the Twins are 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.
- The 70626 Dawn of Iron Doom box incorrectly identifies Acronix's minifigure as "Krux".
- Acronix has an MP3 player on his belt.
- His minifigure also possess an earpiece, which isn't present on his show counterpart.