Sonic CD

Sonic CD is a 1993 platforming game in the Sonic series released for the Sega CD. You play as Sonic the Hedgehog as he attempts to foil Dr. Eggman's plans to take over the game's setting, Little Planet. The game has a time travel mechanic, where Sonic can run past signposts that say "Past" or "Future", and then travel back or forwards in time if he continues to maintain speed.

This game is also notable for introducing two Sonic series mainstays, Amy Rose and Metal Sonic. Both of these characters appear in Sonic games even to this day