Alien X

Alien X is the Omnitrix's DNA sample of a Celestialsapien from the Forge of Creation.

Backstory
Ben acknowledges Alien X as his most powerful alien; however, he cannot afford the cost that comes with becoming the alien.

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. All three speak in unison when Alien X speaks.

As Serena and Bellicus have been arguing for eternity and before they had no tiebreaker, getting them to focus on any present task is difficult at best, leaving Alien X's body trapped in place.

However, in Omniverse, Ben uses Alien X successfully to create a near exact copy of the universe when it gets destroyed by the Anihilaarg.

Appearance
Alien X is a humanoid alien that has white hands. He is all black excluding his hands, which are white. He has tiny white star-like spots all over his body. His eyes are green with no pupils. On his head are 3 horns like Ultimate Way Big.

Unlike most of Ben's aliens, Alien X has five fingers.

In Omniverse, Alien X retains his original appearance, but his chin is now bigger like Diamondhead. He is more muscular and his horns are smaller.

Alien X wears the Omnitrix/Ultimatrix symbol on his chest.

Powers and Abilities
Alien X is omnipotent, being able to warp reality, time, and space to any level he wishes.

Alien X's reality warping is so powerful, that even his mere thoughts can become real.

Alien X can create an entire universe at will, as seen in So Long, And Thanks For All The Smoothies.

Weaknesses
In order for Alien X to perform any action, including simple movement and transforming back, at least two of his personalities must agree to do so. This has proven to be a major weakness, as Serena and Bellicus weren't interested in dealing with present affairs and wanted to finish past ones that weren't possible to deal with without Ben.

In Ben 10,000 Returns, the said weakness was referenced by Paradox, where he revealed that there is an alternate timeline where Albedo transformed into Negative Alien X and was stuck motionless for nearly a year.

Alien X is vulnerable to having his powers absorbed, as Ben and Azmuth have implied that Darkstar and Osmosians can absorb his omnipotent powers.

Alien Force

 * Alien X first appears in X = Ben + 2, where Alien X stops a flood caused by a broken dam. After much fruitless argument, Ben convinces Serena and Bellicus to transform him into another alien (mostly by insulting them). He swears that he won't use Alien X again, as it is not worth the price.

Ultimate Alien

 * Alien X returned to Ultimate Alien in The Forge of Creation, Ben half heartedly used Alien X in hopes of locating the Forge of Creation in his last-ditch effort to stop Ultimate Aggregor from obtaining the universe's greatest power. It was revealed that Ben and Kevin hacked the Ultimatrix offscreen and devised a special lock system to prevent bad guys, like Albedo, from transforming to Alien X. With this, using Alien X now requires two keys to be inserted to unlock Alien X. While Alien X is being hidden from the playlist, the keys that which unlocks him are being kept by Gwen and Kevin, who both own one of the keys. After transforming, Bellicus and Serena start debating about other things as usual. Suddenly Paradox appears, telling Ben that he would not be able to convince Bellicus and Serena to help him out today. Also, Paradox puts himself in danger by going into the presence of Bellicus and Serena who almost voted to destroy him, and changes Ben and himself back into his human form before they could come to a vote.
 * In The Ultimate Enemy: Part 2, Alien X appeared in the flashback.

Omniverse

 * Alien X returns to Omniverse in So Long, And Thanks For All The Smoothies. Alien X successfully recreates the universe.

Ben 10: Alien Force

 * X = Ben + 2 (first appearance)

Ben 10: Ultimate Alien

 * The Forge of Creation (first re-appearance)
 * The Ultimate Enemy: Part 2 (flashback)

Ben 10: Omniverse

 * So Long, And Thanks For All The Smoothies (first re-appearance)

Video Games

 * Ben 10 Alien Force: Vilgax Attacks (alternate timeline)

Ben 10: Alien Force

 * 4" Alien X
 * Alien X (Planetary Powder)
 * Alien X (Alien Creatures set)
 * 10 cm Alien X (DNA Alien)
 * Alien X with Goop (Black version) (Creation Transporter)
 * Alien X (Defender) with Alien Bust
 * Alien X (Alien Creation Launchers)
 * Omnitrix Hero Collection with Alien X hologram
 * Alien X (Alien Rocks)
 * Alien X (Keychain)
 * Alien X (Deluxe)

Ben 10: Ultimate Alien

 * Alien Creation Alien X and Ben
 * Alien X Defender and Vulkanus (DVD and 4 inch action figures)
 * Classic Wildmutt, Nanomech, Spidermonkey Defender and Alien X (Combo pack)

Ben 10 Alien Force: Vilgax Attacks

 * Alien X appeared in the game (only in the CGI movies/clips for Xbox 360, Wii, PS2 and PSP). He is not a playable alien, being replaced by Cannonbolt/Murk Upchuck.

Online Games

 * Ben 10 Alien Force: Alien Attack
 * Fusion Fall (Nano)

Trivia

 * Before Alien X appeared, the opening of Ben 10: Alien Force showed only a silhouette of him, after he did, it showed his full profile.
 * Alien X is a Nano and a former NPC in the game Fusion Fall.
 * The X in Alien X is actually refering to the Roman numeral of 10. Alien X is named like this because he is the 10th alien in the Omnitrix.
 * In Project Exonaut, Alien X is a level 10 suit.
 * In Andreas' Fault, a devoted fan of Ben refers to the Alien X smoothie as a disappointment as well as calling it "filler." This is a reference to Alien X's standing in the series.
 * Ironically, in many promotional images of him, Alien X is posing dramatically (like in the openings to Alien Force and Ultimate Alien), while in the actual series, most of the time, he is frozen in a standing-up position.
 * In A Jolt from the Past, Rook speaks of Alien X, but believes it is just a rumor. Ben tries to convince him that Alien X is real, but Rook doesn't believe him and asks Ben to transform and show him. He later shows Rook that Alien X is real.
 * So far, Alien X has made only one appearance by Ben in Alien Force, Ultimate Alien, and Omniverse. This is because he only uses him in dire situations.