Subject Name: Magnus Opal
Species: Evolved Human (physical boost, Enhanced senses, Increased resistance to disease and poison)
Species Mutation: Advanced Technopathy
Artificial Alteration: Galvan/Cerebrocrustacean based Brain enhancement
Unique Skills: Minor Mana Usage
Reality of Origin: UNUA-K01-B
The "clone" of Albedo and a Omnitrix wielder known to the universe only as Legion. Legion was far more willing to end enemies permanently than Ben in the Prime universe, leading to Albedo deciding to create clone bodies so that, in the event of his death, they would still continue to exist. Unfortunately, when a glitch in the second Ultimatrix turned them into a child, it caused the systems to register them as dead.
Due to the clone body being incomplete, it would take a while before it would awaken. In this time, the same Codon Stream energy that Albedo has imbued himself with caused the clone to gain memories from Legion, this universe's version of Kevin Levin, and the occasional arrival of Legion's future self (or child?), Legion X. The result of this was an individual very different than Albedo himself.
One of the other affects of this, unfortunately, was the breakdown of the clone's genetic code, leading them to kidnap Legion, Kevin, and the technopath Danielle Cooper. Using the Omnitrix and Legion's DNA to stabilize the Codon energy, and using Kevin's power to steal Danielle's technopathy abilities, the clone would also hook themselves up to a machine that would artificially evolve them by 100 generations, altering their appearance and increasing their physical abilities.
Dubbing themselves Magnus Opal (based off Magnum Opus), they would turn themselves into the Plumbers. Despite everything, they would only receive a light prison sentence, due to their near-death derived desperation at the time.
While Legion's memories granted them a better understanding of Azmuth's view of the Omnitrix's purpose, Magnus Opal still sought their own power, even if they were far more caring of other's lives. Thus they would create their own version of the Omnitrix, dubbed the Optimatrix. This would simulate the same 100-generation evolution they applied to their human form, increasing the overall power of the transformations, and reducing weaknesses and vulnerabilities (such as to disease or poison)
On top of this, they would use their Technopathy to get the intellect of their enhanced Galvan and Cerebrocrustacean transformations in their human form, which would then apply to every transformation.
When the pieces of the Potis Altiare began showing up on Earth, Magnus Opal would gather them and reverse engineer them, miniaturizing and applying it to the Optimatrix, further amplifying many of their TFs' power
With the knowledge of Legion X, they would be able to recreate and improve the function of the Biomnitrix, creating a pseudo-Ultimate form for each fusion that would result in a new species.
When last seen, Magnus Opal, on top of advancing technology throughout the galaxy, was found to take one day a week in the form of a Celestialsapien, telling anyone who asked that they wish to convince the alters, Opaia and Orion, to grant them immortality. Time will tell whether they succeeds or not.
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How powerful can an Omnitrix wielder become? Well, considering one of the show writers said the Ultimates could be further Ultimatized, it's hard to really say if there's a limit. And with all the different Trix Trends popping up since Canibal made up the Carnitrix, people have been showing their creative juices, including in making Ben OP, with the Cosmictrix and Omegatrix.
This is basically my idea, making a powerful Omnitrix, while not breaking the scales entirely. The Optimatrix is a tamer version of the Ultimatrix, focused on overall survival. This helps with combat, since stronger powers do help with surviving, but can also be seen with being more resistant to poisons and diseases. Of course, this is more focused on things that are harmful in the short-term - more long-term damage from stuff like sugar and caffeine can still affect them. Still, it prevents the mental affects the Utlimatrix had.
Getting the intelligence of smart aliens in human form comes from one of the Alien Force comics. In Benstorm, Cooper makes a machine to give Ben the same intelligence as Brainstorm, regardless of whether he is transformed into him or not. In the comic, this stops working when the machine is destroyed. Here, it is an indefinite effect.
For the Potis Altiare, while it is clearly a powerful device, it was created long before geniuses like Albedo and Azmuth were around. Combine that with a Cerebrocrustacean brain, and miniaturizing it seems pretty easy. This is different than Sombor, who has yet to reverse engineer his version, as raw intelligence doesn't beat the centuries, if not millenia, of experience that Albedo has, and consequently, so does M.O. Sombor also has to worry about his Potis Altiare burning out.
And since M.O. has the same drive to prove themselves better that Albedo had, they would of course try to do that by convincing their Celestialsapien alters to grant them full control without a court trial influencing the decision - though they only mention immortality to others. They have cheated a little though, as the 100-generation guided evolution has resulted in more cohesive alters than most Celestialsapiens have.
Also, I headcanon here that Albedo becoming a child was a glitch caused by Atomix's energy, because no, Azmuth being a complete dick is not funny. He's supposed to be the smartest being in five galaxies, he should not be doing anything that would justify Albedo's hatred of him.
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??: Whatever you do, don't give other magic users your real name, Toma. Just in case.
Magnus: You did, V.
??: HA! You think my parents named me Sombor Viraxis? They weren't emos!