Plot
Supervillain Megamind and his polar opposite, superhero Metro Man, are extraterrestrials of different species who were both independently sent to Earth as infants before a black hole destroyed their planets. Though both land in Metro City simultaneously, Metro Man is raised in a rich mansion and Megamind in a prison. At the school they attend, Metro Man is well-liked by his classmates, while Megamind is relentlessly bullied until he reaches his breaking point, setting off a rivalry between him and Metro Man.
Over the years, Megamind and his fish-like assistant and best friend Minion frequently and unsuccessfully battle Metro Man for control of the city. On the day of the new Metro Man Museum's grand opening, Megamind escapes from prison, kidnaps news reporter Roxanne Ritchi, and lures Metro Man to an abandoned observatory to rescue her. Megamind blasts him with a sun-powered death ray; Metro Man is unable to escape, having stated that the copper-lined observatory roof weakens his powers. Overjoyed, Megamind takes over the city and executes a crime spree, but eventually becomes depressed and purposeless without Metro Man to oppose him.
Megamind decides to blow up the Metro Man Museum to forget the hero, but sees Roxanne is also there; as he runs, he dehydrates the museum's curator, Bernard, turning him into a small cube. Disguised as Bernard using hologram technology, Megamind talks to Roxanne, whose remarks inspire him to use Metro Man's DNA to create a new superhero to fight. Megamind perfects the formula, but during a fight between him and Roxanne in his lair, he accidentally injects it into Roxanne's cameraman Hal Stewart, who is infatuated with her.
Disguising himself via hologram as Hal's "Space Dad", Megamind trains Hal to become a superhero. Hal, seeing this as a chance to win Roxanne's heart, accepts and takes on the name "Titan" (which he later mistakes as "Tighten"). Megamind begins to date Roxanne while disguised as Bernard, and he and Minion have a falling out over Megamind's apparent lack of interest in committing further crimes. Roxanne rejects Tighten when he comes to court her and Tighten later witnesses her on a date with Megamind disguised as Bernard. After a heartbroken Tighten leaves, Megamind's disguise fails and Roxanne rejects him as well.
Megamind arranges to fight Tighten the next day, but soon learns that Tighten is now using his powers to conduct a crime spree. Tighten offers to ally with Megamind, who deliberately reveals his disguises and deceptions to goad Tighten into fighting. Angered, Tighten savagely beats Megamind in the fight. Realizing that Tighten is uninterested in justice and means to kill him, Megamind traps Tighten in a copper ball, but it fails when Tighten easily breaks out. Going to a reluctant Roxanne for help, she and Megamind arrive at Metro Man's old hideout, the old school house they attended. There, they discover that he is still alive, having faked his weakness and death after having become tired of protecting Metro City, followed by renaming himself "Music Man" to pursue his dream of becoming a musician. Megamind attempts to enlist his help against Tighten, but Music Man refuses; he instead encourages Megamind to become the city's new hero by telling him that a hero will always rise to defeat evil.
Dejected, Megamind willingly returns to prison, while Tighten goes on a rampage and kidnaps Roxanne when she tries to reason with him. On a televised message, Tighten holds Roxanne hostage and demands that Megamind fight him. Regretting his actions of trying to kill Metro Man in the first place, a redeemed Megamind escapes from prison with the help of Minion and reconciles with him. He goes to confront Tighten, using holographic disguises to appear as Metro Man, with Minion as Megamind, to frighten Tighten away and rescue Roxanne. However, Megamind's speech patterns reveal his identity and Tighten attacks Megamind, throwing him into the stratosphere. Dehydrating himself into a cube and landing safely in a fountain, Megamind re-hydrates next to Tighten and extracts the DNA from him, reverting him back to his former self. After Hal is arrested, Megamind rekindles his relationship with Roxanne, while the city celebrates Megamind as their new hero. The museum is rebuilt in Megamind's honor; a disguised Music Man additionally attends the grand re-opening.
