Ben 10 / Generator Rex Crossover - Heroes United

The story begins with a mysterious rift opening in the skies above New York City. 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 appears on the scene to stop the rift, but are unable to do anything before Rex arrives with Six and Bobo. Holiday then gets a scan that shows something is coming through the rift, and Rex finds himself face to face with Humungousaur, and the two begin battling it out in Central Park. During their skirmish, a strange metallic creature also appears and heads into the city, with Bobo and Six on it's trail while Rex continues to battle Humungousaur, who changes into Diamondhead, much to Rex's shock. Rex is also troubled by the fact that his ability to cure has no affect on his opponent.