Bowser and Dr. Eggman have met via a dimensional rift. They have the plan to build the Time Eater 2, using it to mess up both the Mario and Sonic universes. They manage to attack Mario's 29th birthday and Sonic's 23rd birthday parties, sending all their freinds across time and space. Both heroes try to attack but fail. They wake up in a white void seperatly and eventually meet in World 1. Sonic tells Mario that they are traveling through time and that they must save their friends. The 2 set off to save everything!