Sonic the Hedgehog CD or Sonic CD is a platformer video game created by Sega. It is part of the "Sonic the Hedgehog" series. It was released for the Sega CD game console in 1993. In chronological order it is after the first game and "before the sequel." The game involves the use of a time travel system that allows Sonic to travel to both the past and the future in a level. Each zone has four variants: the "past," the "present," the "good future," and the "bad future." Each has different graphics, music, enemies, and obstacles. The game introduces two characters to the "Sonic the Hedgehog" series: Amy Rose, a pink female hedgehog with a hammer as a weapon, and Metal Sonic, an evil robotic version of Sonic.