Kevin Levin (Classic)/Omniverse flashbacks

While he was trapped in the Null Void, Kevin was found by the Rooters, who conducted experiments with his Osmosian powers on Alan Albright, Helen Wheels, Manny Armstrong and Pierce Wheels, transforming them into the Amalgam Kids, making them do nasty things. After that, Kevin fled, only with Servantis controlling his memories, convincing him that he had "alien blood". 
As shown in a flashback in Weapon XI: Part 2, Kevin first met Argit when he gave a caged Argit a leaf to eat. Kevin then said that he was going back to Earth and save it and intended to take down Ben. On Earth, Kevin discovered Argit had stowed away and threatened him to start running. He and the Amalgam Kids confronted Ben, Gwen, and Max. Ben managed to avoid a shot from Kevin and transformed into Eye Guy. Eye Guy pinned Kevin down. However, Kevin did this to get Ben to come closer so he could touch the Omnitrix, causing Kevin to mutate again. Kevin, like Ben stated, started to go insane again and even attacked his allies, the Amalgam Kids. Kevin was eventually stopped by Argit who used his quills. Kevin and the Amalgam Kids were sent back to the Null Void, but an enraged Servantis wiped out their memories and sent them away. Servantis then abandoned the plan to destroy Ben after Ben stopped wearing the Omnitrix.
Sometime later, in the Null Void, Kevin and Argit moved some objects around and they both talked about how difficult it was to bring the objects together. A robot named Otto arrived and said that he was going to use the objects to help them get out of the Null Void. Otto tricked Kevin and Argit into turning on the device and escaped without them, leaving the now-dismayed Kevin and Argit trapped in the Null Void. 
At some point later, Kevin was brought out of the Null Void by Thaddeus J. Collins, who was being possessed by Zs'Skayr and tied to the Null Void portal using Plumber technology. Collins asked Kevin to use his absorbing powers to mine Hedorium underground. Kevin was mining for Hedorium in a dark cave when he encountered Ben (who was accompanied by Gwen and Lucy and his friends Cooper and Jonesy). After Cooper examined the technology as Kevin asked him to disconnect him from the portal, Ben disagreed with Kevin's request as he had done a lot of bad deeds. Kevin then told Ben that the Earth would be in danger. Ben took Lucy and Jonesy to find out about the problem as Gwen and Cooper dealt with Kevin. 
While Ben as Eye Guy, Lucy and Jonesy fought Max holding a weapon, Kevin teased Cooper about being Gwen's boyfriend but both of them stated they were just friends. As Eye Guy, Lucy, and Jonesy defeated Max, Cooper tried to pull the connection but failed. He then reprogrammed Kevin's connection to let him pull the portal like a kite. Gwen blasted at the portal to separate the ionic bonds as they headed to join Ben, Lucy and Jonesy. Ben laughed at Kevin because he was still connected to the portal, Kevin said it was better than being stuck to one spot. As the group walked further into the caves, they saw a portal which things came out off. They headed up only to see Collins, who was revealed to the children to be possessed by Zs'Skayr, and that the Transmat Portal was for the Ectonurites to come in from their homeworld. Due to the collective efforts of all the kids, everyone was saved when suddenly the Null Void portal started to pull Kevin. Ben, Gwen, Lucy, Jonesy and Cooper helped to pull Kevin in order to prevent him from being pulled into the Null Void portal, but they failed to do so when Ben lost his grip on Kevin's hand.
Kevin and Argit eventually managed to secretly escape from the Null Void at the same time and Kevin resumed his life. Two years after breaking away from Servantis, Kevin began working on his car. Not satisfied with a simple standard model, he began outfitting it with alien tech, and to this end, traveled to Khoros to acquire a Tetramand engine block for it. Since the tech couldn't be given to an outsider, he wooed the then teenage Princess Looma Red Wind and successfully defeated her combat earning the right to marry her in three years thereby making him a part of the family and was given the engine as a gift.
Kevin visited home at least once between his escape from the Null Void and prior to Alien Force.