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This article is about the crossover. You might have been looking for the online game of the same name.

Ben 10/Generator Rex: Heroes United is a crossover episode animated in Generator Rex's art style with an appearance by Ben Tennyson. It constitutes the tenth and eleventh episodes of the third season of Generator Rex, and the fiftieth and fifty-first episodes overall.[MH 1]


When a mysterious rift appears over Manhattan, Rex is on the scene to see if there is trouble coming. However when Humungousaur comes from the clouds, Rex gets a bit more than he bargained for! Rex begins battling it out with the Vaxasaurian in Central Park, not realizing that Humungousaur is actually Ben Tennyson. Ben soon discovers he's in an alternate dimension and that he and Rex must team up to overcome their combined foes.[note 1]


The story begins with a mysterious rift opening in the skies above New York City, attracting the attention of Providence. Meanwhile, Rex is sparring against Agent Six, while musing about his need for a "theme song" (and briefly performing a take on the original Ben 10 theme song) before getting the alert about the rift. Providence, at the same time, is unable to do anything before Rex arrives with Six and Bobo. Rex attempts to touch the rift to see if it has something to do with nanites when Holiday gets a scan that shows something is coming through the rift, and Rex finds himself face to face with Humungousaur, who knocks Rex back into the park beneath them. During their skirmish, a strange metallic creature also appears and heads into the city, with Bobo and Six on its trail while Rex continues to battle Humungousaur. Just when Rex thinks he has the upper hand on the monster, Humugousaur transforms in a flash of light into Diamondhead. Rex attempts to cure Diamondhead but to no avail, which surprises Rex.

Meanwhile, Six engages the creature and manages to cut a piece of it off, and when Holiday's scans give insufficient data, the piece is given to Rex's older brother, Caesar. Diamondhead and Rex's battle then winds up on the Brooklyn Bridge after Rex lands a well-placed punch. Diamondhead gets up and transforms into Lodestar, attempting to counter his opponent's metal-based abilities. However, Rex quickly adapts and blasts Lodestar with his Slam Cannon into a billboard. It breaks free of its binding, which forces the two to stop fighting. Lodestar transforms into Rath to save the news reporter, Diane Farrah while Rex saves the other civilians. During Rath's discussion with Dianne, Rex does a surprise drop on Rath and once again attempts to cure him, only for it not to work again. After attempting to explain himself, Rath decides to transform back into his true form, Ben Tennyson. Ben is shocked to learn that no one knows about him. Just then, Six appears with the mechanical creature from before, which self-destructs and renders him comatose, and Rex mortified and angered.

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Diamondhead fighting Alpha

In the Providence defect group's infirmary, Holiday explains that the creature was nanite in origin, but somehow completely different from any EVO they have ever encountered. White Knight points out that part of it got away and that they were now searching for it. Ben says that they are probably dealing with a parallel universe issue. Holiday doubts his assumption, stating that parallel universes are just a theory to which Ben replies that he has traveled to many of them. Ben says that they need to go out and search for it. Rex remarks that there is no way Ben can escape, but Ben transforms into Big Chill, phases out of his containment unit, and flies off with Rex in hot pursuit. Big Chill visits the area where Bellwood should be and transforms back into Ben, and finding that himself, Gwen, Max, and Kevin do not exist in this world, nor does Mr. Smoothy (instead it is Bob's Biscuit Barn), Ben finally comes to grasp that he must be in an alternate universe and both finally come to a truce. Caesar appears and seemingly prepares to attack the two with a ray gun, which was actually intended for the energy ball, which is revealed to be the Alpha Nanite, the first nanite and a creation of Caesar's. The Alpha Nanite begs Caesar to help him stabilize a new body to which Caesar refuses. Ben as Diamondhead knocks Alpha away from Caesar and manages to force Alpha to leave.

After escaping the creature, Caesar explains that he created Alpha as a means of controlling the nanites during the Nanite project, but its form is unsustainable and every body it builds burns out in short amount of time. When Alpha attempted to take organic bodies, this forced Caesar to banish it to another empty dimension. Ben surmises it must have been the Null Void where it wound up, and that Alpha must have possessed alien life to sustain itself. Caesar explains that the damaged ray gun was to stop Alpha, who then attacks and destroys his research pod. Caesar escapes via the escape pod, leaving behind the two heroes. Ben transforms into Cannonbolt and saves Rex, to which the latter complains of the smell.

Alpha attacks Providence in order to absorb the EVOs inside for their nanites. When Ben and Rex arrive, they fight the Alpha where it attempts to absorb Rex's Omega-1 Nanite but fails. Ben and Rex eventually manage to drive Alpha off, and slowly bond after sharing their origins during a small game of hoops.

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Rex and Ben accidentally wear each other's jackets

White Knight reveals that Alpha has gone to the Bug Jar, which is the largest concentration of active nanites on the planet after the Nanite Event. White Knight and the heroes arrive, only to find they are too late to stop Alpha from absorbing the nanites of all the EVOs that were in the Bug Jar to become a colossal monster that begins to attack the three of them. Alpha is unable to absorb Rex's Omega-1 Nanite, so he decides to hack Ben's Ultimatrix which gives him access to his own nanite corrupted version of it and three of Ben's aliens; Heatblast, Alpha-Arms, and Humungousaur. During the battle, Ben transforms into a new alien named Shocksquatch, which only lasts a few seconds but enough to stop Alpha momentarily. Using an odd form of teamwork, Rex is able to disable Alpha's imitation Ultimatrix powers, but is ensnared by his enemy and robbed of his Omega-1 Nanite, leading to Nanite Alpha to transform into a colossal crab-centaur-like being calling itself Alpha-Omega, the beginning and the end.

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Upgrade merged with Rex

As the now nearly unstoppable Alpha-Omega rampages through the Bug Jar, synthesizing the ruined structures in order to create new nanites for itself, Rex has doubts about himself now that his most powerful builds are gone. Ben, however, comes up with a plan, and transforms into Upgrade and merges with Rex, thus providing him with the upgraded versions of his original six builds. After a couple seconds, the duo then takes on the Alpha-Omega, to which they hold their own for a short while. At the last minute, Rex comes with a plan, and both do a final bout of teamwork. Rex locates the Omega-1 Nanite inside of Alpha-Omega and shoots Ben as Cannonbolt directly at the monster, using his Slam Cannon, which forces him into a large cloud-like entity. Rex then uses his abilities to begin to dense the nanite cloud into a small sphere. While this happens, Caesar appears and extracts the Omega-1 Nanite. Attempting to dispose of Alpha, Caesar then opens a rift for Ben, who transforms into Murk Upchuck and swallows the compacted Alpha as he departs to the Null Void and back to his own Earth, but not before weirding out Rex one last time.

In the epilogue, Rex is overjoyed that Six has recovered, and wonders if he'll ever see Ben again. Six suggests that they possibly will if fate had ordained for them to meet once already. Caesar appears and injects the Omega-1 Nanite into Rex. Rex doubts that Caesar could have accidentally brought the alpha Nanite, although Caesar assures him that there is a 99.998% chance that it is Omega-1.

In the final moments, in the depths of the Null Void, Alpha begins to stir within its prison of matter, causing it to glow and crack apart.

Noteworthy Events[]

Major Events[]

Ultimatrix Alien Debuts[]

Replica Ultimatrix Alien Debuts[]



Aliens Used[]

By Ben[]

Flashback Cameo Aliens[]

By Alpha[]


Rex: (singing to the theme of the Ben 10 theme song) It started when the nanites went ka-pow upon the scene. Transforming all the lifeforms like nothing you've ever seen. But there's one lucky hombre that can make them build machines: He's Gen Rex.

Rex: Have anything to say for yourself before I commence with the face-stomping?
Humungousaur: Yeah! You've just made a humungous mistake!

Humungousaur: You and your partners are gonna call it quits right now, and I'll keep the pounderizing to a minimum.
Rex: I was gonna say the same thing, only in Spanish.

Reporter: Thank you, Wh-- Who are you?
Rath: Seriously? I'm the cat who's all that! The Rath Attack! Eh, but I have heard of other things.

Ben: There's no Mr. Smoothy here. That's messed up.
Rex: My partner is in a coma. If you're stressing over a frozen drink, YOU ARE TOTALLY GETTING PUNK-BUSTED!!!

Rex: Feel like giving me a hand?
Ben: How about four? (Transforms into Four Arms)
Rex: I'm starting to like the way you think, Ben 10.

Ben: It started when the Omnitrix fell out of the sky; I was ten years old.
Rex: Six years ago, the Nanite Event changed everything!
Ben: And there's alien DNA in the Omnitrix!
Rex: And that's how I could build stuff with the micro machines in my body!
Ben: Now Kevin, Gwen, and I are the Plumbers!
Rex: Plumbers? And I thought Providence was a dumb name!
Both: HA HA HA!

Ben: If this is the Bug Jar - where are the bugs? (Large swirl of gray wind appears)
Diamondhead: Whoa, what do you call that?
White Knight: I call the entire nanite population of the Bug Jar.

White Knight: Don't let it get to Rex- if it drains his nanites... (talking about Alpha)
Diamondhead: Game over. Understood!
Rex: It already tried to eat me - that didn't work.
White Knight: That thing was made to control machines.

Rex: I could use an alien right now! (gets absorbed by Alpha Nanite)
Ben: Great idea, but a certain nanite monster busted my watch!

Rex: Do something - ANYTHING! (being absorbed by Alpha Nanite)
Ben: (Tries to throw a tiny rock at Alpha, but misses, and hits Rex)
Rex: Do something BETTER!
Ben: I could try calling it names!
Ben: (to Alpha Humungousaur) Hey Jerkasaur! You're a loser!

Naming and Translations[]

Language Name Origin
German Vereinte Helden | Ben 10 & Generator Rex
Das Ding aus einer ganz anderen Welt
United Heroes | Ben 10 & Generator Rex
The thing from a whole other world
Italian Ben 10/Generator Rex: Heroes United Ben 10/Generator Rex: Heroes United
Polish Ben 10-Generator Rex: Przymierze Bohaterów Ben 10-Generator Rex: Hero Alliance
Portuguese (Br) Ben 10/Mutante Rex: Heróis Unidos Ben 10 / Mutant Rex: United Heroes
Romanian Ben 10 şi Generator Rex: Ajutoare Neaşteptate Ben 10 and Generator Rex: Unexpected Help
Russian Бен 10/Генератор Рекс: Работа в Команде Ben 10 / Generator Rex: Teamwork
Spanish (HA) Ben 10-Generador Rex: Héroes Unidos Ben 10-Generator Rex: Heroes United
Turkish Ben 10-Generator Rex Heroes United Ben 10-Generator Rex Heroes United


Voice Actor Role(s)
Yuri Lowenthal Ben Tennyson
Daryl Sabara Rex Salazar
Dee Bradley Baker Humungousaur
Big Chill
John DiMaggio Rath
Bobo Haha
Black Pawn
David Kaye Shocksquatch
Grey DeLisle Rebecca Holiday
Diane Farrah
Wally Kurth Agent Six
Jennifer Hale Black Knight
J.K. Simmons White Knight
Freddy Rodriguez Caesar Salazar
Michael Emerson Alpha


  • Ben has access to new and old aliens, placing the events of this special after Ben 10,000 Returns.
    • For Rex, this special takes place after Double Vision, as he uses his enhanced goggles. However, this special aired before Double Vision.
  • Ben claims that he goes to parallel worlds all of the time, referring to adventures to places such as Legerdomain and the Forge of Creation.
  • Caesar explains that Alpha was one of the very first nanites during the nanite project in Abysus.
  • Rex and Ben both tell their origin stories.



  • In some shots, the black outline around Humungousaur's lips is missing.
  • When Diamondhead says "Lucky punch", his jaw does not move.
  • Rex's BFS is drawn incorrectly during the fight on the bridge.
  • Lodestar's mouth opens when the billboard starts to fall.
  • When Rex tries to remove the nanites from Rath, Rath has dark green pupils.
  • In one shot, Rath has five fingers. Additionally, in one frame after saving Diane and her cameraman, one of Rath's eyebrows is colored white, similar to his reboot counterpart.
  • When Rex is first holding Six, his glasses are off and his eyes are closed, then when Rex tells Ben it was all his fault, Six has his glasses on.
  • Before Ben transforms into Big Chill, the containment unit is much wider than it should be.
  • When Big Chill phases through the containment unit, he retains his normal appearance instead of being translucent. His wings are also drawn differently.
  • When Big Chill talks to Rex after escaping captivity, the insides of Big Chill's eyes are light green, and the outside is dark green.
  • In one shot, Diamondhead's head has an error.
  • Ben says that the Ultimatrix has the DNA of over a million aliens, even though the DNA is actually on Primus.
  • When Cannonbolt falls to Earth, the sound of the Ultimatrix being activated plays even though Ben is already Cannonbolt.
  • Four Arms' hologram faces away from Ben.
  • In Ben's flashback:
    • One Echo Echo clone has black lips.
    • Heatblast and Stinkfly's designs were taken from the Original Series.
    • Goop's Anti-Gravity Projector is missing.
    • Cannonbolt's eye dashes are green.
    • Wildmutt's missing his middle teeth.
    • Big Chill's wings are missing.
    • Ripjaws has one pink eye and one green eyebrow.
    • Diamondhead's spikes are missing.
    • Ampfibian's white swipes in the middle of his body are missing.
    • Upgrade only has one line on his body.
    • Four Arms is also missing part of his body, he cuts off at XLR8's head.
    • Jetray is missing black borders around his eyes.
    • Chromastone's teeth are green rather than white.
    • Cannonbolt's white body is darker, especially compared to Echo Echo right above him.
    • Spidermonkey's eyes appear pure black, save for the green pupil, rather than having green around them in a ring.
    • Four Arms, Upgrade, and Rath are all in their Ultimate Alien designs rather than their new designs for Heroes United.
  • During Ben's flashback, Young Ben is initially shown facing away from Omnitrix's containment pod, despite not doing so in And Then There Were 10.
  • When Ben explains his origin to Rex, he says that there is DNA in the Omnitrix even though he is wielding the Ultimatrix.
  • When Ben transforms into Big Chill for the second time, he has five fingers, and the patches on his right arm are drawn incorrectly. Furthermore, for a split second before he flies off, there is less black on his neck.
  • When Ben transforms into Upgrade, the Ultimatrix symbol is missing, and only appears when he merges with Rex.
  • The sound of the Ultimatrix being activated plays when Rex uses the Slam Cannon against Alpha while merged with Upgrade.
  • When Ben reverts from quite a few aliens in this crossover, the sound of the Ultimatrix being activated and then hit down is played.


  • The part where Ben transforms into Rath for the second time was cut in the Asian and Polish versions.
  • The Sky Slyder is the only accessible machine that Rex doesn't use in the special.
  • The episode was first shown at New York Comic-Con 2011, several days before its official premiere on television.[AC 1]
  • Unlike in Ultimate Alien, Ben does not shout the names of his aliens after transforming into them in this episode, because the writers forgot to write it.[DR 1] He also does not use any of his Ultimate forms, whereas he does so in Hero Times Two.
  • Gwen and Kevin are absent from the episode as the crew didn't have room for everyone.[JK 1]
  • The episode originally had two working titles, Rex X and Gen 10.[MH 1] The latter title was later used, albeit slightly modified, for Ben Gen 10.
  • The Providence defect group's discussion up until the scene where Ben and Rex board Caesar's ship was storyboarded by Miyuki Hoshikawa.[MH 1]. Ben and Rex's conversation with Caesar on his ship was storyboarded by Fill Marc Sagadraca,[FMS 1] while the scene immediately following it, where Alpha attacks Caesar's ship, was storyboarded by Richard Pose.[RP 1] Some scenes are different in the storyboards compared to the final version of the episode.
    • Big Chill breaks out of the containment unit instead of phasing through it.
    • The chase scene between Big Chill and Rex is slightly longer.
    • Big Chill catches Rex's Smack Hand instead of freezing it.
    • Rex invites Ben to board Caesar's ship, instead of the scene cutting ahead after Caesar tells Rex they need to leave.
    • When Ben says the Ultimatrix has the DNA of over a million aliens, he pulls the sleeve of his jacket back to reveal the Ultimatrix, instead of pulling the sleeve over the Ultimatrix to cover it up.
    • Ben and Rex leave Caesar's ship through an escape pod, instead of Ben using Cannonbolt.
  • Man of Action had thought of Ben and Rex meeting each other, from the very first day,[AC 1] but it took a while for the idea to get approved.[STS 1]
  • Duncan Rouleau considers Heroes United his favorite Ben 10 film,[DR 2] even though it is a special and not a movie.
  • Upgrade and Rex working together is one of Joe Kelly's favorite parts of the episode.[JK 2]


  1. The original synopsis provided on the back cover of the Heroes United DVD erroneously reads: "When a mysterious rift appears over Manhattan, Rex is on the scene to see if there is trouble coming. However when Humungosaur comes from the clouds, Rex gets a bit more than he bargained for! Rex begins battling it out with the Vaxasaurian in Central Park, not realising that Humungosaur is actually Ben Tennyson. Ben soon discovers he's in an alternate dimension and that he and Rex must team up to overcome their combined foes."[merch 1]


Crew Statements[]

Miyuki Hoshikawa[]

Fill Marc Sagadraca[]

Richard Pose[]

Duncan Rouleau[]

Joe Kelly[]

Steven T. Seagle[]


Audio Commentary[]

Ben 10: Ultimate Alien Episodes