When Ben meets a young Generator Rex on the run from a hostile Providence, he must work through a the still alive series of misunderstandings, and defeat the dark wizard Hex in order to save the world from a malfunctioning Omnitrix infecting the world's human population with alien DNA.
The episode begins with Heatblast battling a living tree near a family roasting marshmallows. Heatblast burns the tree, almost causing a forest fire, until Gwen and Grandpa Max put a blanket for the burned tree. Hex appears and uses the powers of Pans flute to make more living trees. The family returns wanting to thank Heatblast for getting rid of the living tree, but Heatblast tells them to run. Hex makes more living trees and begins to overpower Heatblast. Gwen tells Heatblast to go for the flute and shoots a fire at him, causing him to drop the flute. Heatblast burns the flute turning the living trees into normal trees, and makes hex mad as usual. Heatblast turns back into Ben and Gwen and Max congratulate him, hoping this would be the last adventure of their summer vacation. Ben thinks it’s not the end but Gwen brings up their past adventures proving Ben wrong. Ben refuses to believe that his summer vacation is almost over and takes Gwens s’more. Ben walks in the forest complaining about school and hallucinates his s’more talking to him. An unknown person swoops in and takes the s'more from Ben. It is revealed to be Rex. Rex shares the s'more with Bobo Haha. Ben as Cannonbolt shows up and chases them to get back his s'more. Once he finds out they ate it, he rages. Rex builds the Big Fat Sword, shocked at the results. He fights Cannonbolt, and manages to escape from him. It's not long before Cannonbolt catches up. Bobo notices that Canonbolt isn't an ordinary EVO. He spots a piece of technology on his stomach. Rex runs up to Cannonbolt, and causes the Omnitrix to malfunction using his nanites.
Shock Rock: Ohhh, we're going to be in so much trouble if we mess up this monument. Agent Six: Make it easy on yourself and surrender. Providence would prefer you in one piece. Shock Rock: I don't know who this Providence guy is, but, you can tell him, no thanks! (Fires energy at Six, dodges and kicks Shock Rock) Ugh. That hurt. You don't skip leg days do ya? Agent Six: Providence is an organization. Created to contain extinction events before they start. Shock Rock: Well, where were you when that kid broke my watch and stole my s'more, huh? Wait, did you say "extinction"? Agent Six: Yes. Which is why I have to contain you and your EVO generator first. Then I'll deal wit Rex. Shock Rock: Whoa, whoa. I'm no EVO, bro! I'm one of a kind! Well, 10 aliens of a kind. Nah, never mind. Agent Six: With that device, you are a liability. Even more than Rex. Hex: Yes. A liability who’s own flawing shall be his undoing.
Diamondhead: Step away from the robot and his monkey! Rex: I am not a robot, I've got nanites in my body. Bobo: Don't correct the walking chandelier when he is actually helping us.
Diamondhead: What now? Rex: Bobo and I usually run. Diamondhead: I usually wreck stuff till Gwen comes up with a better plan. Rex: Is Gwen a monkey? Diamondhead: (laughs) I so wish she heard that.
Ben: What happened to your parents? Rex: Good question. I kind of have a hard time remembering stuff.
The special has musical motifs due to the reboot sharing the same composer as the original Generator Rex series.
Rex mistakes Ben's aliens for rampaging EVOs before teaming up to take down the main villain.
Ben calls Rex "Robot Boy".
One of the family member, the wife resembles the one from the season 1 episode, The Beast Inside.
Hex's plot is a revamped version of Vilgax and his classic counterpart's respective plots of amassing an army of Omnitrix aliens.
The way Hex's plot is executed is similar to Outbreak, as both involve the Omnitrix being busted and turning other people into copies of his aliens before the Omnitrix is fixed, reverting everyone back to their normal selves.
The episode shares some similarities to Ben 10: Destroy All Aliens as both movies have the Omnitrix malfunctioning and turning people into aliens.
Much like in Ben 10 Versus the Universe: The Movie, Ben uses all of his regular aliens from season 4 in this special.
The name of this episode was first discovered on Andrei Lenart's portfolio site and a Spanish dubbing website.
The idea of Ben 10 and Generator Rex characters living in the same universe is a repurposed concept that the crew tried to use in the Classic Continuity. However, the idea never came to pass back then due to both series having different toy licenses.[MoA 1] This special is the crew's way of rectifying the scrapped "shared universe" concept.[DR 1]
A crossover between the Ben 10 reboot and Generator Rex was first hinted by Duncan Rouleau, though it was intended to air during season 3[DR 2] before being postponed for season 5.[DR 3]
Duncan also confirmed Vic Chao would be be making a guest appearance, but avoiding spoiling which character Chao would be voicing.[DR 4]
This is the second movie/special to crossover with Generator Rex, the first being Ben 10-Generator Rex: Heroes United. As such, Daryl Sabara and John DiMaggio both reprise their roles as Rex and Bobo from the original Generator Rex series.
Stinkfly, Wildvine, Overflow, and Grey Matter's appearances in this movie event were first hinted when Duncan stated that aliens that were removed from the active playlist over the course of the series (excluding Upgrade and Gax) would return in a future season.[DR 5]