Dr. Robotnik is on vacation, but he's still planning to take over the world, and this time he's built several robotic copies of Mario. However, the robots eventually turned good and turned against their creator. With a new army of feline henchmen, led by Captain Robocat, Robotnik's plan ensues, so Sonic must unleash the Mario robots to help him defeat Robotnik's entire army and have the final battle against Robocat.