Alien X

Alien X is the Codon Stream's DNA sample of a Celestialsapien from The Forge of Creation.

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

Alien X has a black body filled with tiny white stars, white hands, green eyes and three horns protruding from his head.

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 together 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.

Powers and Abilities
Alien X has shown to be omnipotent, able to warp reality and time/space itself, becoming nearly invincible.

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

Because Alien X is Ben's most powerful alien or Ben thinks, as Dwayne states that Alien X is not the most powerful alien in the Codon Stream, but does carry the most risk.

Weaknesses
In order for Alien X to perform any action, including but not limited to, simple movement and transforming back, at least two of the three personalities must agree to do so. This reveals 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 (with a comical scene where Bellicus reopens a discussion on whether or not to save the dinosaurs from extinction).

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.

On another note, despite his omnipotence, 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 and Ultimate Alien

 * 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 off using Alien X afterward, as it is not worth the price even when there is immeasurably strong and powerful universal power that comes with the form.
 * In Darkstar Rising, Kevin suggests to use Alien X against Darkstar. Ben declines as there would be no stopping him if he had absorbed Alien X.
 * Alien X returned to Ultimate Alien in The Forge Of Creation, Ben halfheartedly 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.

Ben 10: Alien Force

 * X = Ben + 2 (first and only appearance in Alien Force)

Ben 10: Ultimate Alien

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

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 X-Box 360, Wii, PS2 and PSP). He is not a playable alien, being replaced by Cannonbolt/Upchuck.

Trivia

 * Before Alien X appeared, the opening showed only a silhouette of him, after he did it showed his full profile.
 * Alien X is a Nano and an NPC in the game Fusion Fall.
 * In Project Exonaut he is a level 10 suit.
 * In Andreas' Fault, a devoted fan of Ben's refers the Alien X smoothie is a disappointment as well as calling it "filler." This is a reference to Alien X's standing in the series.
 * Paradox has hinted that Ben will one day use Alien X successfully.
 * It is unknown how Ben's association with Paradox affects Ben's relationship with Bellicus and Serena, since Ben is the voice of reason in Alien X and Paradox is not supposed to be within 500 light years of any Celestialsapien.
 * Ironically, in many promotional images of him, Alien X is posing dynamically (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.