Alien X is the Omnitrix's DNA sample of a Celestialsapien from the Forge of Creation.
Alien X has three personalities: Serena, the 'voice of love and compassion', Bellicus, the 'voice of rage and aggression', and Ben, the 'voice of reason'. After his conflict with the Galactic Gladiator, his speech is made by only one voice at a time, as the key to Alien X was to give each of the personalities control over the body when it is most appropriate for them to do, with the other two limiting the one in control in order to not have full control over a Celestialsapien's power. After his victory, Alien X was also accepted to the halls of the Celestialsapiens on the Forge of Creation, being called upon the need for him to fight cosmic battles after he took the place from the Galactic Gladiator.
Alien X is a humanoid alien whose entire body is solid black, excluding his hands, which are white. He has tiny white star-like spots all over his body, giving him the appearance of a starry night sky. His eyes are green and lack pupils, and his forehead bears three horn-like protrusions.
He now wears a green and silver gladiator armor as well as a green and silver helmet, and sports "hair" similar to Ben. His horns now represent who is in command of Alien X: if the lateral horns are smaller than the middle one, Ben is in control. If they are angled but practically have the same size, it is Bellicus. If they are smooth and have the same size, it's Serena.
Serena and Bellicus also have minor changes, with Bellicus having a flat nose and a green beard, and Serena having eyeliners.
Powers and Abilities
Alien X is omnipotent, being able to warp reality, time, and space with ease and at any level he wishes. Even his thoughts can become real. In short, Alien X can do anything.
Alien X can create time waves to reverse events.
Alien X can create and recreate an entire universe at will.
Alien X is nearly invulnerable, as he was completely unharmed when the Anihilaarg destroyed the universe around him.
Alien X can self-duplicate, create galaxies to suck in other beings, and travel at high speeds. He also possesses superhuman strength and the ability to grow to a gigantic size. He is skilled at hand-to-hand combat.
Alien X possesses telekinesis and is capable of deflecting energy attacks.
Alien X can bond his power with other Celestialsapiens if they agreed.
Alien X is vulnerable to having his powers absorbed, as Ben and Azmuth have implied that Darkstar and Osmosians can absorb his omnipotent powers.
Other Celestialsapiens, like the Galactic Gladiator, can harm Alien X.
Alien X cannot survive on Anur Vladias.
Alien X's actions onto reality can be neutralized and reversed by the intervention of other Celestialsapiens.
Alien X would not survive omniversal or timeline destruction unless he combined his powers with a group of Celestialsapiens in advance.
As the three personalities don't have to agree anymore, the body is always put to the limit, which makes Ben extremely tired after using him, sometimes putting the Omnitrix on Recharge Mode just to avoid transforming for a few hours or maybe even days.