Sonic Generations is a 2011 platform video game developed by Sonic Team and published by Sega for the PlayStation 3, Xbox 360, Nintendo 3DS, and Microsoft Windows. An installment in the Sonic the Hedgehog series, the game—which was produced in commemoration of its twentieth anniversary—follows Sonic and his sidekick Tails as they form an alliance with their past selves to stop an evil entity from erasing all time. It features two gameplay styles: “Classic”, which plays from a side-scrolling perspective like that of the original Sega Genesis Sonic games, and “Modern”, 3D levels similar to those in Sonic Unleashed and Sonic Colors.