Retcons

Throughout the Ben 10 franchise, various changes in the continuity (otherwise known as retcons) have been made. Below are most of the retcons made in the Classic Continuity, a lot of which were off-screen information subject to revision.

According to Matt Wayne, they take what they want and ignore what they don't like.

Ben 10: Alien Force

 * The Plumbers are now an intergalactic police force, when it was established in the original series that they were a secret government organization comprised of humans only , several of which had a racist attitude towards aliens.
 * Gwen is revealed to be part alien, which explains her proficiency in magic.
 * The origin behind Kevin's powers has been altered for the series. Primarily, he is now an alien hybrid with the ability to absorb a shell of material around his body instead of a mutant that has the ability of absorbing, storing, and redirecting energy. He inherited his powers from his father, Devin Levin, instead of getting them as a result of a mutation.

Crew Statements' Retcons

 * Vilgax was originally stated to be 15 feet tall. However, Humungousaur at his base height of 12 feet is shown to be the same size as him.

Pop-up Retcons

 * In the original series, the Forever Knights were like "Anti-Plumbers", exploiting unusual threats instead of fighting them. In Alien Force, the Forever Knights are revealed to be highly xenophobic.
 * Originally, Null Guardians were the only indigenous lifeforms in the Null Void. This is retconned with the introduction of the Null Void Settlers.
 * Originally, the Omnitrix only held thousands of DNA samples. This was retconned in Alien Force, as firstly, the Omnitrix was revealed to be a wireless receiver for the Codon Stream, instead of containing DNA, and secondly, the Codon Stream contained over one million DNA samples.
 * The Chimera Sui Generi have been changed from what was established in the original series:
 * All female Chimera Sui Generi had a dark "beauty mark" somewhere on their center face tentacle, but none of the females seen in Alien Force have them.
 * Most Chimera Sui Generi were trained from birth for combat and craved any chance for it, but in this series, Vilgax states that most of them are innocent people.

Ben 10: Ultimate Alien
Retcons from previous series explained:
 * It is revealed that Kevin's stepfather is actually a good person and that Kevin wasn't kicked out, but he went insane with power, destroyed the house, and ran away.
 * The Nanochip queen featured in Ben 10: Alien Swarm is revealed to be a decoy created by the real queen to avert suspicion towards her.
 * Events of Ben 10: Race Against Time are retconned into an alternate timeline. As such, Eon's backstory has been changed (including his species). Furthermore, Chronians and the planet Chronia no longer exist in the Prime Timeline.
 * The retcons made to the Forever Knights in Alien Force are explained and/or fixed. The Forever Knights were divided into many separate factions, thus explaining the different goals and appearances, before being unified for the purpose of riding Earth of alien life following the return of the organization's founder.

Ben 10: Destroy All Aliens

 * Gwen performs a tracking spell in the movie even though she in Ben 10 Returns: Part 1 that it was her first time doing so.

Ben 10: Omniverse

 * In Alien Force and Ultimate Alien, two out of Alien X's three personalities needed to agree in order to perform an action. In Omniverse, all three have to agree.
 * Although it was established in Alien Force that Ben last saw Vilgax when he was 10, a flashback showed that he had an encounter with Vilgax was when he was 11.
 * The Plumbers' Helpers now have different origins; they are shown to be humans whose appearances and DNA were altered when Kevin used his powers on them and their alien donors.
 * According to the Azmuth's Father, the pyramids were built by Tetramands. This was proven wrong in Omniverse, where an ancient stone tablet shows that the pyramids were in fact built by humans with the "help" of Blukic and Driba.
 * Echo Echo's object duplication and flight were glitch powers.
 * Way Big's enhanced speed in The Widening Gyre was a glitch power.

Retcons From Previous Series Explained

 * The retcons made to the Plumbers in Alien Force are explained and/or fixed. The original Earth Plumbers were a separate group until they joined the intergalactic Plumbers at some point between the events of the original series and Omniverse flashbacks. This also introduced alien Plumbers working at Earth bases.
 * The retcons made to Kevin in Alien Force are reversed. While Kevin is still considered an Osmosian, the term actually refers to a subspecies of human with a unique genetic component that gives them powers rather than a different species. Also, neither Devin Levin, the planet Osmos V, nor the sun Osmos exist because they were all fake memories implanted by Servantis.

Crew Statements' Retcons

 * Originally, the citizens of Vilgaxia had their own opinions whether Vilgax is a hero or otherwise. However, nobody voiced their thoughts publicly for sure. This is slightly retconned when Milleous claims that capturing Vilgax would demoralize the people of Vilgaxia enough to make them surrender, and when the news is out that Vilgax succeeded in escaping, the Chimerans put up such a fight that the Incurseans are forced to retreat.

Pop-up Retcons

 * Originally, XLR8 was the only Kineceleran on Earth because the slow rotation of Earth made other Kinecelerans sick after a few days. This is retconned, as several Kinecelerans reside in Undertown.
 * Originally, the Anur System had an anti-matter sun. However, this is no longer true, considering the massive cobweb structures lining the system.
 * In the original series, it was stated that all Loboan cubs had green eyes, whereas adults had red and pale orange eyes. This is retconned, as the Loboans seen on Anur Transyl have eyes of varying colors.
 * Hex's skull facepaint was the same as that worn by the warriors of Bezel. This is retconned, as Hex's facepaint is revealed to be a tattoo and Bezel is revealed to be a person, not a civilization.
 * The Charms of Bezel were not magic. Instead, they were advanced Bezelian technology that seemed magic to Earth. This is retconned, as Bezel is revealed to be a person.

Merchandise Information Retcons

 * Instead of being brought to life by an environmental disaster, the Galvanic Mechamorphs were brought to life after one of Azmuth's projects went awry.
 * Encephalonus IV was a gray, cloud-covered planet with lightning bolts constantly ripping through the sky in an unending electrical storm of spectacular cumulonimbus activity unrivaled by any in the universe. This is retconned, as it is shown that the planet has relatively normal weather.
 * The Necrofriggians used to be the only living beings on Kylmyys. This is retconned with the introduction of the Psycholeopterrans.
 * Originally, nothing actually lived on Anur Transyl. This is retconned, as Anur Transyl is shown to be inhabited by many species native to the Anur System.