Recap / Sonic Generations

Sonic celebrates his birthday with his friends, but the festivities are cut short by the sudden appearance of a monster known as the Time Eater, who creates several holes in spacetime, whisking away Sonic and his friends and trapping them in a white void.

Sonic soon travels to the Green Hill Zone. There, he finds and rescues Tails, who had been petrified after being sucked into the void. Eventually, they meet up with the past versions of themselves. Both the present and past Tailses conclude that time and space is being damaged by the Time Eater's presence, and both the present and past Sonics have to set things right.

Both Sonics race through various settings from throughout their history, along the way rescuing their friends, battling old rivals, and collecting the Chaos Emeralds.

After restoring their history and collecting all seven Chaos Emeralds, the Sonics go to confront the Time Eater, only to find that it is being used by Dr. Eggman. Having discovered the Time Eater after the failure of his previous world domination scheme and observing how it could erase time, Eggman decided to use the creature to erase his past failures and ultimately reign supreme. A plot of this magnitude, however, required additional assistance from an equally evil genius: thus, he enlisted the aid of his past self.

The Time Eater initially has the advantage over both Sonics, but with encouragement from their allies and the power of the Chaos Emeralds, both Sonics assume their super forms and pursue the Time Eater. They both emerge victorious, and with the Time Eater's defeat, Sonic and company return to his birthday party. The present Sonic and Tails bid farewell to their past selves as they depart for their original timeline.

Meanwhile, both the past and present Eggmans find themselves trapped in the white void from earlier, with no way to escape the void or each other as their alliance breaks down into petty squabbles.