Eunice

The Unimatrix, self-nicknamed Eunice, is a prototype Omnitrix which can absorb and contain DNA of various different species. She is also one of Azmuth's creations.

Unitrix form
In her true form, Eunice is the Unitrix, a core similar to the Omnitrix and Ultimatrix.

Unlike future models, the Unitrix resembles a container instead of a watch, but does feature a control dial that, when pressed down, turns it to its mobile DNA form (in this case, Eunice).

Human form
Eunice's base mobile form is a teenage human girl. She has shoulder-length blonde hair with a single bang and bright green eyes.

When Ben's Team first found her, Eunice was completely naked, then she borrowed Ben's jacket so she wouldn't be seen naked. Afterwards, she borrowed a pink tank top, white shorts and brown flip-flops from Gwen. Since working for Azmuth on Primus, she now sports a white jumpsuit with black stripes.

There are green rectangular markings on the back of Eunice's neck. When they are pressed, Eunice turns back into the Unitrix.

In Omniverse, Eunice now wears a white dress with a black collar and one stripe in the middle. She wears black fingerless gloves and now wears black leggings. Her hair is now shorter and wears a black hairband, which resembles Gwen's season two look in Omniverse.

Ultimate Alien
Sunder was hired by Azmuth to find the Unitrix when Azmuth lost it.

The Unitrix's pod was discovered in the forest at the same time Ben's Team was driving for a camping trip. After encountering her, she stayed with them for the day, bonding with Ben (who had recently broken up with Julie), the two of them were soon attacked by Sunder, who shut Eunice down and attempted to get away before Kevin and Gwen stopped him as Kevin restarted the Unitrix again.

While the four of them scuffled with Sunder, Azmuth arrived and cleared things up. He stated that Eunice was the Unitrix, a prototype version of the Omnitrix created when Azmuth wanted to preserve alien DNA by placing genetic samples in individual Unitrixes that can animate themselves to take on the appearance, and use the abilities, of the DNA samples that were uploaded into them for protection. Azmuth states that when Gwen cut her hand, trying to open the pod containing the Unitrix, her DNA was sampled and randomized to make a human form for the Unitrix (explaining why Eunice has blond hair while Gwen has orange/red hair). Following a brief argument, Ben allowed Azmuth, under a compromise, to take on Eunice as one of his assistants on Primus.

In Simian Says, Eunice was tending to DNA in the Codon Stream, where she found the Arachnichimp DNA had some degradation. She went to Aranhaschimmia to get a fresh DNA sample, where she found the Xenocyte infestation and stayed to help. She was eventually thrown into a pool of Xenocytes and turned into a DNAlien. She fought Swampfire, but was cured. She eventually used Simian to revert all the Arachnichimp DNAliens to normal.

Eunice was seen in a flashback in The Ultimate Enemy: Part 2.

Omniverse
Eunice makes a cameo in The Most Dangerous Game Show.

Powers and Abilities
Eunice is capable of storing DNA of various different species. Unlike the Omnitrix and Ultimatrix, Eunice is not connected to the Codon Stream, and unlike the completed Omnitrix, she can only hold one DNA sample.

Eunice was shown to be able to copy powers and abilities of animals (a rabbit, a bear, and a snake) and then to manifest traits of these animals (enhanced jumping, strength and flexibility) without changing her form. According to Dwayne, whatever Eunice absorbs, she only has the abilities of it for ten or so minutes.

In addition, local wildlife seemed to be attracted to Eunice to the point where normally shy animals would gather around her, and more dangerous animals (like a bear or snake) would be tamed by her presence.

Prior to Simian Says, Eunice received an upgrade to have a one way subspace link to Primus for uploading DNA samples.

Weaknesses
If the markings on the back of her neck are pressed, Eunice will revert to the Unitrix.

Having her link to Primus active, Eunice can cause parallel signal interference which could cause the Ultimatrix to lose its connection to Primus if it is nearby. Eunice can shut it off to prevent this.

Eunice can be turned into a DNAlien. She can be cured by turning the Unitrix off and back on again.

Ben 10: Ultimate Alien

 * The Transmogrification of Eunice (first appearance)
 * Simian Says
 * The Ultimate Enemy: Part 2 (flashback; cameo)

Ben 10: Omniverse

 * The Most Dangerous Game Show (first re-appearance; cameo)

Trivia

 * According to Azmuth, Eunice is dangerous.
 * According to Derrick J. Wyatt, her Omniverse design is based on 60's go-go outfits.
 * Eunice's mark on the back of her neck resembles the brand of a Pulse l'cie from Final Fantasy XIII.
 * The reason why the Unitrix landed on Earth is because it was seeking an Omnitrix core like itself.
 * At the beginning, Eunice's origin was similar to Supergirl's arrival on Earth; she appeared in a space pod, she was fully naked, she had the DNA of Earth's heroes, and she didn't know what was happening.
 * Eunice's role in the series somewhat mirrors that of the character Nia from the series Tengen Toppa Gurren Lagann: both were/are artificial life-forms embedded in the human genome and both have a relationship with the protagonist (Eunice's relationship to Ben being a minor one). Coincidentally, Yuri Lowenthal voices both Ben and Simon, the main character of said anime.
 * Eunice being afraid of going back into storage is similar to Jessie from Toy Story 2 being afraid of being put into storage.