When Professor Charles Xavier became possessed by an unknown evil, no one could predict what the result would be. Soon the evil manifested itself as the ultra-powerful being called Onslaught! Possessing nearly unlimited levels of psionic power. Onslaught used Xavier's knowledge of the X-Men to defeat them. But when the the [sic] remaining mutants and the world's heroes separated Xavier from Onslaught, the villain only changed form, growing even more powerful. Bent on the destruction of all mankind, Onslaught can only be stopped by the combined forces of all the world's heroes!