A terrible accident caused the birth of the Lord Ultron Sigma to rise, it's up to one boy in AvengersLabs to fight back with the Avengers, the Fant4stic, the X-Men, Captain Marvel, Dr. Strange, Hulk and the Agents of S.M.A.S.H., Devil Dinosaur, Spider-Man, and otherworldly superheroes like Saitama, the One-Punch Man, to stop the Ultron Sigma Legion from overtaking the new Super-Hero Megacity.