Just how powerful is Ben 10 (strongest fictional character he can beat)?

[Ultra_Sonic]

This is Ben Tennyson, at the end of the original timeline.. With his most powerful alien forms at play, who is the strongest character (strongest fictional characters across any and all media) that he can beat.

[Len Ikari145]

Given that Ben can freely access Alien-X by the end of the original series, you need someone on the level of a well-fed Galactus to be a threat to him.

[T-1000]

It all comes down to whether or not Ben can control Alien X. At the end of Omniverse, he can but this completely disregards the nature of this particular being. Alien X is a Celestial Sapien, meaning he possess god like reality warping power and can only ever use that power when his two personalities agree. Yes, Alien X has multiple personalities, one of them his rage and aggression and the other his compassion and gentleness. It's only ever when these two personalities agree on a course of action that Alien X can even move which is why most of the time, if Ben ever does end up transforming into this alien, he ends up being completely immobilized. Ironically his most powerful transformation is also his most useless one. He was shown once in Omniverse getting his two selves to let him have full control but this seemed like more of a one time thing. By the end of the series, he again transformed but this time no explanation was even given as to how he convinced them to agree. Essentially, Ben 10 Omniverse was a huge step backwards in terms of the writing in a lot of respects

Basically, flip a coin. If you subscribe to the notion that Ben has no problem anymore convincing Alien X to do whatever he wants, then Ben has godlike power and it would take a reality warper well beyond Silver Surfer/Doctor Strange to give him any kind of fight.

If you are skeptical as I am, then Ben still has an assortment of powerful aliens to choose from and is extremely formidable depending on how well he can change between his different transformations (something else that has not been consistently portrayed across the show) but would have a hard time putting down anyone in the Hulk's weight class.