Kevin's Mutations

Kevin's mutations are caused by his Osmosian ability to absorb DNA and energy. By absorbing DNA and energy from Ben's aliens or the Omnitrix or Ultimatrix, the energy combined with the DNA will cause him to mutate into an amalgamation all of unlocked aliens.

Kevin 11
Shortly after trying to get revenge on a gang of bullies that had threatened him, Kevin was exposed to an Omnitrix feedback that he accidentally absorbed. The energy was sufficient enough so that Kevin could shapeshift between any of the original 10 aliens in the Omnitrix. However, during a fight with Four Arms on the Golden Gate Bridge, Four Arms put Kevin into submission and, at first, looked like he was going to kill him. Instead, he deliberately missed and walked away, stating that Kevin was never worth it. Kevin however, wanted to continue fighting and became enraged. His rage, combined with all of the energy and DNA he absorbed, caused his powers to spiral out of control, causing him to mutate him into a hulking chimerical behemoth fusion of the 10 original starter aliens of the Omnitrix, which Kevin dubbed Kevin 11 (due to having all of the powers of the 10 aliens from the Omnitrix plus his own powers). Vilgax called Kevin 11 "a misshapen chaotic amalgam of creatures... from the Omnitrix", his powers weren't as strong as Ben's and only had one-tenth of their original strength (however, in terms of physical strength, he was stronger than Four Arms). However, he is capable of mixing the abilities to create a powerful result, such as using Heatblast's flames and Stinkfly's goo to form an explosive attack, or using XLR8's speed, Four Arms's strength, and Diamondhead's fist for, as he put it, "one mean punch". Kevin 11 also proved strong enough to hold his own against the Megacruiser robots, Technorg, and even Vilgax in a one-on-one fight.

After approximately 5 years in the Null Void, his human DNA overwrote the alien DNA, causing Kevin to lose this form in the Alien Force timeline.

In ...Nor Iron Bars a Cage, it is revealed how Kevin changed back to normal from Kevin 11. When he becomes a Null Void prisoner, he met another prisoner named Kwarrel, who Kevin 11 soon came to help for. Kwarrel taught Kevin 11 how to control his anger and powers. Soon enough, Kevin 11 becomes sane again, and returns to his human form.

Ben 10: Alien Force
{C In Vengeance of Vilgax, while Ben was trying to hack the Omnitrix, the Omnitrix overloaded. Kevin tried to help Ben by trying to override the system, but instead he got blasted by the feedback that the Omnitrix created. The blast rewrote his Osmosian DNA, causing him to mutate into a segmented, living colossus composed of the various matter aliens in the Codon Stream are made of. During his time in this form, Kevin learned that he can shapeshift his limbs into various tools, weapons, and forms and had limited regenerative abilities. In addition, his enhanced strength and durability were further increased.

In Trade-Off, Kevin teamed up with Darkstar to turn back to normal. He succeeds but lost his powers, making him useless in battle to the team. Gwen finds out what he did and goes after Darkstar. Darkstar then absorbs all of her power, and Kevin realizes the only way to save her is to stop Darkstar. After stopping Darkstar, he got his mutation back (so did Darkstar), and Gwen was saved.

In Time Heals, Gwen tried to turn him back to normal by going back in time and stopping the disaster, but later learned that it had to happen after Charmcaster imprisoned Ben and made Kevin a rock slave.

Kevin turned back to normal in The Final Battle: Part 2 when the Omnitrix is destroyed. According to Max, it must have been the Omnitrix's energy what had kept him in that form, meaning that, unlike his first mutation, his DNA would not have restored itself so long as the Omnitrix was functioning.

Appearance

 * Kevin's frame and briefs.
 * Taedenite: Left half of his face.
 * Concrete: Right half of his face, left half of his chest and back, upper right half of his chest and back, and left arm.
 * Metal: Lower right half of his chest, upper right half of his back, lower back, stomach, and right arm.
 * Wood: Legs.

Powers and Abilities

 * Enhanced strength and durability, regenerative abilities, weapon manifestation

Ben 10: Ultimate Alien
In The Forge of Creation, in order to stop Aggregor from absorbing the powers of a newborn Celestialsapien, Kevin had no choice but to absorb the Ultimatrix's powers and turn into, as Vilgax would call it, a misshapen chaotic amalgam form of the creatures of the Ultimatrix. This form, dubbed Ultimate Kevin, is very powerful and very quickly and easily defeated Ultimate Aggregor and drained his powers. However, Kevin's personality has become even worse than it was in the original series.

Throughout ...Nor Iron Bars a Cage, The Enemy of My Enemy, and Absolute Power, Ultimate Kevin goes rampant on attacking people who either owed him or he wanted revenge on. Fortunately, Kevin still seems to have some control his sanity, as he spared an opposing Gwen. Either way, Kevin is too powerful for anyone to beat and Ben thinks "putting him down" is the best option.

In Absolute Power, Kevin's self-control is almost entirely overtaken by his insanity. His Osmosian instincts have caused him to develop an insatiable hunger for energy and begins draining the life force of anyone unfortunate enough to cross his path, regardless of whether or not they had powers. Ben still thinks that eliminating Kevin once and for all would be the best choice.

Gwen, however, sees that the power is controlling Kevin's mind. Gwen puts her own life at stake and tries to help Kevin by talking. He reveals to her that he still had a single shred of his humanity that let him stay away from Gwen, knowing that his remaining willpower would be overwhelmed by his insanity and that he would end up draining her if he got the chance. Ultimately, despite his love for Gwen, Kevin is overwhelmed by his hunger and he ends up partially draining her of her life force and powers, nearly killing her. He then becomes obsessed with her overwhelming amount of energy and ends up tracking her over the rest of both episodes (though his feelings for her prior to his mutation become mixed with his insanity, as seen when he commenting that he thinks she's deliberately avoiding him and how he shows anger when Cooper tries to stop him from killing her and tries to kill him as well).

Ultimate Kevin was cured in Absolute Power: Part 2, thanks to the efforts of Ben, Gwen, Cooper, and Darkstar. However, Darkstar becomes Ultimate Darkstar by absorbing the powers from the Dominus Librium which had absorbed Kevin's powers. Fortunately, Ben anticipated this from the beginning and presses a button which not only strips Morningstar's new powers, but returns the abilities to their rightful owners as well as reviving the five Andromeda Aliens.

Kevin 11,000
In Ken 10, which takes place in an alternate timeline, Kevin escapes the Null Void with the help of his son, Devlin, and says that during his time there, he absorbed the power of other aliens trapped with him, 11,000 at least, becoming Kevin 11,000.

Trivia

 * Kevin's mutations are an Osmosian trait (which he inherited from his father) as the full Osmosian villain Aggregor is shown to be capable of absorbing and assimilating alien DNA which allows him to gain their abilities and causes a slight mutation (though nowhere as extreme as Kevin's). Kevin's mutations are a result of this ability, though he is unable to control his mutations and has trouble keeping a stable mental state due to inexperience (as Kevin 11,000 is able to keep a stable mental state and has shown the ability to retain certain alien abilities he has absorb while in human form, such as XLR8's super speed).
 * Kevin's alien mutations all have the frame of Four Arms (red, bulky, and two sets of arms).
 * During his third mutation, Kevin's wings seemed to have shape-shifting abilities as whenever the hood unfolded it seemed to be thinner than when folded up and the wings seemed to lose and gain certain aspects/parts when unfolding and would "fuse" together to form the cape when folded up.
 * Each of Kevin's mutations have a unique trait to them before/after being cured for example:
 * After being cured from his first mutation, his clothes are completely intact even though the initial transformation completely destroyed his clothes (except his cargo shorts).
 * His second mutation destroys his clothes completely (except his briefs). This isn't undone upon being cured unlike the first mutation. His second mutation is the only one in which he retains his original body frame and does not lose his sanity. That was because it was not an alien mutation like the first, but it rewrote his Osmosian DNA and he did not absorb the feedback. When Ben hacked the Omnitrix and damaged it during Alien Force, it sent out a wave of energy that rewrote Kevin's Osmosian DNA, only possible due to his Osmosian abilities.
 * Ultimate Kevin, unlike the first, doesn't restore his clothes, with only his pants intact.