- "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 a cosmic starfield 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.
- Paradoxes- Celestialsapiens are seemingly susceptible to paradoxes. This may or may not include life draining forces and magic.
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.