Sonic the Hedgehog CD is a 1993 platform game for the Sega CD developed and published by Sega. The story follows Sonic the Hedgehog as he attempts to save an extraterrestrial body, Little Planet, from Doctor Robotnik. Like other Sonic games, Sonic runs and jumps through several themed levels while collecting rings and defeating robots. Sonic CD is distinguished by its time travel feature, a key aspect to the story and gameplay. By traveling through time, players can access different versions of stages, featuring alternative layouts, music, and graphics.