Ben Tennyson (Classic)/Omniverse flashbacks

One year after the Original Series, Ben, who (along with his cousin) was 11 years old, continued to live in Bellwood and used the Omnitrix to help people and defeat any of the terrestrial and extraterrestrial threats that his team encountered as well. He also went on weekend trips with them.
In A Jolt From the Past, Ben as Stinkfly fought a Nosedeenian. After reverting back to normal, he grabbed a Mr. Smoothy cup and trapped the Nosedeenian in it. However, the Nosedeenian escaped the cup and duplicated. Ben transformed into Feedback and absorbed the energy out of the Nosedeenians, which made them go to sleep.
In Trouble Helix, the Tennysons met Malware, an incomplete Galvanic Mechamorph accidentally created by Azmuth, who lost his patience and kidnapped Albedo, Azmuth's assistant, to complete himself. Eventually, he was turned into a more powerful form, only to be defeated by Diamondhead.
In The More Things Change: Part 1, Ben as Four Arms fought Malware. While at first, it appeared that Four Arms was winning, Malware managed to grab the Omnitrix and forced Four Arms to revert back into Ben. Malware confronted Ben and taunted him about his defeat, which allowed just enough time for the Omnitrix to activate again. Ben transformed into Feedback and quickly defeated Malware. During the fight (as revealed later in both Of Predators and Prey: Part 1 and Of Predators and Prey: Part 2), Malware had successfully created a blueprint by absorbing Omnitrix.
In It Was Them, Ben, along with Gwen, defeated Dr. Animo, in an unknown way.
In Malefactor, the team visited the Plumber base in Mt. Rushmore. There, they were attacked by Malware who was seemingly defeated by a Tachyon Cannon. However, this just transformed him into a more powerful version of himself. He was defeated, although he was just a distraction so that Khyber could sample a rare Psycholeopterran.
In Of Predators and Prey: Part 2, Ben battled Phil who was being used as a test subject for the Nemetrix.
At school in Arrested Development, Ben raised his hand to answer a question and was picked by the teacher but did not know the answer and slouched in his chair, making Billy Billions upset, who had his hand raised. In gym class, he fiddled with his Omnitrix and was picked by a female team leader. Ben was seen as Diamondhead who caught a criminal. Billy tried to zap him but ended up zapping himself to Dimension 12.
In Showdown: Part 1, Ben transformed into Feedback many times to defeat the Violet Offenders, somehow stop a fire, and practice his powers. Due to Ben's constant use of Feedback, Azmuth came to Earth to warn Ben that this was affecting his other transformations. Ignoring him, Ben transformed into Feedback again and prepared to fight Malware who had returned. This resulted in Feedback being destroyed and Malware being seemingly killed when he was overloaded by the Omnitrix's energy.
In Showdown: Part 2, Ben and Gwen exited the Rustbucket 2 when Max brought them back to Ben's house. Ben was depressed and upset about losing Feedback. Azmuth arrived and explained that Ben never learned anything from winning and that losing Feedback was hard for him. Ben said that Feedback was like a part of him, but Azmuth said that Ben could learn something from losing Feedback. Ben eventually forgave his future self, and this allowed 16-year-old Ben to regain Feedback.
thumb|Ben teaming up with his 16-year-old self
In Ben Again, while battling Eon, 11-year-old Ben's mind got switched with that of his 16-year-old self. As 16-year-old Ben, he found the clues laid down by the 16-year-old Ben who was inhabiting 11-year-old Ben's body. 11-year-old Ben managed to get his body back and defeat Eon.
In Special Delivery, Ben accidentally threw Mr. Baumann's truck into space as Way Big during a fight against Dr. Animo and his Mutant Mosquito.
In Evil's Encore, the team encountered and defeated Dr. Animo again during their visit to the Plumber base at Mt. Rushmore after he managed to take control of the base to use the Plumber satellite network in order to spread his mutation ray over Earth.
In Mud is Thicker Than Water, Ben tricked Gwen into disliking their cousin Lucy by putting sludge all over her comb.
In Bengeance is Mine, Ben was captured and tied upside down in ropes by Vilgax in his ship. Vilgax then threatened to feed Ben to his numerous Squid Monsters, but Ben broke free and transformed into XLR8. XLR8 tried to battle Vilgax, but he was grabbed by a Squid Monster. The flashback was cut short here, so it is unknown how Ben landed up in this situation or how he got out of it.
In The Vengers, Ben saved some people from an exploding building and captured Kangaroo Kommando as XLR8. With this, Ben made new enemies, in the forms of Captain Nemesis who saw him as a rival and Will Harangue who saw him as a vigilante.
In Weapon XI: Part 2, the team fought Kevin again, who was associated with the Amalgam Kids at the time. Kevin once again absorbed the Omnitrix's energy and underwent another mutation that caused him to transform into an alien hybrid that consisted of the other 10 aliens Ben unlocked in the Original Series. After Kevin trapped everyone in vines and planned to kill them, Argit managed to knock out Kevin. Afterward, Kevin, Argit, and the Amalgam Kids returned to the Null Void.
In The Ballad of Mr. Baumann, Ben encountered and defeated Vulkanus once again after he and Max entered Mr. Baumann's store.
In From Hedorium to Eternity, Ben, Gwen, Lucy, Cooper, and Jonesy met Kevin underground and together stopped Zs'Skayr and his Ectonurite minions from taking over the planet. Ben learned to trust Kevin, but he once again got stuck in the Null Void. Ben and Gwen did not encounter him again until four years later when they had developed into teenagers.
At some point later, for unknown reasons, Ben removed the Omnitrix and never wore it again for the next four years.