"Ben 10/Generator Rex: Heroes United" is an extended crossover special between Ben 10: Ultimate Alien and Generator Rex. Taking the form of an extended episode of Generator Rex, with it having an appearance of Ben Tennyson from Ben 10: Ultimate Alien and it being written by Man of Action, the creator of both shows. Heroes United aired on November 25, 2011, on Cartoon Network, taking up a one-hour time block. As a special event, it premiered at New York Comic Con 2011. Heroes United was universally acclaimed by fans of both series, and has hit the top 100 on iTunes. This special is the second Cartoon Network crossover after the 2007 crossover special, The Grim Adventures of the KND. Plot A mysterious rift begins to open in the skies of Manhattan. Meanwhile, former agent of peacekeeping organization, "Providence", Rex Salazar is sparring against fellow agent, Agent Six, while musing about his need for a theme song, before getting the alert about the rift. Providence appears on the scene to stop the rift, but are unable to do anything before Rex arrives with Six and Bobo. Doctor Holiday, scientist and love interest of Agent Six, then gets a scan that shows something is coming through the rift, and Rex finds himself (unknowingly) fighting against Ben Tennyson, in the form of Humungousaur. During their skirmish, a strange metallic creature also appears and heads into the city, with Bobo and Six on its trail. Continuing their fight across New York, Ben switches to Diamondhead, Lodestar and finally Rath as Rex continues to try curing him, believing him to be an EVO mutated by rogue nanites which he deals with on a regular basis; an annoyed Ben demands Rex stop as he doesn't even know what an EVO is. Changing back to human form, Ben is shocked that no one has heard of him despite being a celebrity back home. Then, Six appears with the creature, which self-destructs and renders him comatose, leaving Rex mortified and angered at Ben. At Rex's hideout, Ben is locked up in a containment unit, while Doctor Holiday explains that the creature was nanite in origin, but somehow completely different from an EVO, and that Ben didn't appear to have any nanites present in his body before his fight with Rex. Ben offers to help deal with the creature but is denied, and easily escapes into the night as