Sii

Sii is a shapeshifting alien from the twenty-third dimension. She appeared in the Back in Action: Alien Universe Shorts episode Infernosphere, where she was defeated by Ben and co (Julie, Gwen, Kevin, and Ship). Ben mentioned that the team had fought her before that time, where she was in the sphere form of Cannonbolt. She is apparently bent on bringing Ben back to her father in the twenty-third dimension so that she may take her place as Queen, and properly take the throne from her father.

Appearance
Sii's natural appearance is as a glowing blue and white cube. The blue represents her shapeshifting organs and biology, while the white represents her source of energy, personality, and memory. The cube cannot be in anyway penetrated. The cubes of Sii's species would be useful as armor, but when her species dies, the blue parts of the cube, which hold together the cube as well, melts like acid. The personality and memory can be used to sustain one of her species in a temporary body.

She has a beautiful, high-pitched voice in most of her forms.

Powers and Abilities
Sii's most notable power is that which allows her to shapeshift into anything, gaining whatever she's transformed to's powers. These powers are artificial, though. Unless Sii has full knowledge on how a device, alien, or object works, she cannot fully mimic something (such as the Omnitrix), only look like it and act somewhat like it.

When she uses her powers, her forms are much larger than the real thing. She normally ends up the size of most Earth skyscrapers (as Ben has noted). This has been because she's not able to concentrate enough to make her forms actual size. All of her forms also retain her blue and white glow. When one of her species grows older, they are able to add one layer of skin to hide the blue and white.

Known Transformations

 * Arburian Pelarota (in sphere form; after seeing Cannonbolt in battle)
 * Snake (with limited intelligence; after seeing Ssserpent on the streets of Bellwood)
 * Aerophibian (Jetray's species; after seeing Jetray almost defeat her)

Back in Action: Alien Universe
In Infernosphere (Shorts), she is defeated by Ben as Jetray after figuring out that Sii transforms into anything powerful that she sees. She used Snake and Aerophibian forms.