- "I call him Alien X. He's my most powerful transformation. With just a thought, he can do pretty much anything."
- ―Ben Tennyson
Alien X is the Omnitrix's sample of a Celestialsapien from the Forge of Creation.
Alien X has a humanoid appearance with transparent skin that appears to have an active galaxy inside. He has two eyes, and three horns that are growths caused by the transdimensional knowledge he possesses.
Omnitrix placement is unknown.
- Reality Warping- Alien X can do whatever he wants to do. If he can think of it, he can do it.
- Meta-Teleportation- Alien X is the only version of this transformation that exists throughout time and space. All of the Bens through the timeline have access to this version of Alien X.
- Omnilock- The ability to exist outside of everything, including the Omniverse.
- "Guys, I'm not a god...It's not my place to alter reality at will just because I can. If I treat the universe like my own custom playground, what kind of world would I be saving? It wouldn't be genuine. It wouldn't be...life."
- ―Ben Tennyson
- Three-Way Agreement- In order for Alien X to perform any action, all three of his personalities (Ben, Bellicus, and Serena) must agree to do so, but Ben circumvented this drawback at age 16.
- However, Bellicus and Serena could refute Ben's unlimited access to Alien X at any time, should they ever wish to do so.
While Alien X has yet to make an appearance, he has been hinted at multiple times so far:
- In Chapter 5: Oversight, his hologram was shown on Ben's Omnitrix during a flashback.
- In Chapter 6: Weightless, Vlad taunted Ben into transforming into Alien X, but Ben resists it.
- In Chapter 7: Fold, Ben directly mentions Alien X, and explains why he refuses to use him in battle. During Ben's explanation, Alien X appears in a flashback.
- In Chapter 8: Risen, Kevin again tries to urge Ben to use Alien X.
- In Chapter 10: Again, Eon tells Vlad he will need to kill Ben while he is transformed as Alien X. Later on, Danny says Ben should have used Alien X earlier while he was in an angered state caused by his rapid Ghost form evolution.
- X comes from Latin numeral for 10.
- "But Hey, Alien X" has become a meme in Ben 10 and Debate communities, referring to Kuro's original controversial video on his channel that pinned Ben Tennyson against popular fictional heroes, like Goku and Superman.
- Alien X is Ben's most powerful transformation.