The battle against evil. A never ending cause that spans across infinite universe. Despite how different each and every reality may be, there is one constant. Good vs Evil.
But what happens when the evil forces of two separate worlds come together? Can one world's heroes handle another world's villains? The Elements of Harmony can handle any magical foe, but what will they do when their foe sends legions of mechanical monsters against them? And while the Freedom Fighters can smash through any machine, can they stand against the darkest of spells and darkest of souls? Can the heroes, who have such different tactics and stories, overcome their differences to take on the task at hand?
But above all else...is there enough room in this crossover to fit both Rainbow Dash and Sonic's egos? I hope so.