Ben 10/Generator Rex: Heroes United is an hour-long crossover special that originally premiered on Cartoon Network on November 25, 2011. It features a team-up between Ben Tennyson from Ben 10: Ultimate Alien and Rex Salazar from Generator Rex. Plot Summary

However, the true fan service came during the climactic battle. When the threat of Alpha became too great, the creators pulled out the ultimate trump card: Alien X. At the time, Alien X was considered Ben’s most powerful form—virtually a god—but was unusable due to the arguing personalities within the suit.

"Ben 10: Heroes United" received generally positive reviews from fans and critics. The movie was praised for its action sequences, character interactions, and nostalgic value.

More than a decade later, the 45-minute special remains a masterclass in how to blend two distinct creative visions into a cohesive, high-octane thrill ride.