The sequel to the record-shattering Sonic the Hedgehog and Mega Man crossover is here! You saw what happened when Worlds Collide, now brace yourself for when WORLDS UNITE! The vicious conqueror Sigma has escaped from Mega Mans future and has invaded Sonics world to enact his plans for universal domination! Sonic and Mega Man unite once more to stop the vile villain -- and this time the worlds of Sonic Boom, Mega Man X and guest stars from other major Sega and Capcom franchises are joining the fray! You wont want to miss this crossover of epic proportions!