Dr. Eggman and Dr. Wily are locked inside their flying fortress-the Wily Egg! Inside are all manner of powerful defences, including Metal Sonic and Bass! Outside is an army-almost every Robot Master ever made. Dr. Light's life is on the line and two worlds teeter on the edge of destruction. Enter Sonic, Mega Man and an army of their own! Sonic's friends join Proto Man, Rush and Duo in an epic all-out battle to break through to the evil doctors, rewrite two realities and save their home worlds! It won't be easy, but Sonic and Mega Man have a knack of overcoming the impossible.