Sigma--the brilliant villain from the future--has fused the worlds of Sonic the Hedgehog and Mega Man together! Now he feeds on the super-planet's energy to become unstoppable! It's up to Sonic and Mega Man to raise an army to fight the time-hopping villain. Joining them are the Freedom Fighters, the Robot Masters, X and his Maverick Hunters, Sticks and her friends, and--Dr. Eggman and Dr. Wily?! But it won't be easy, as Sigma uses his powers to reach across space and time to recruit an army of his own! It's a battle of epic proportions to save the Unified World!