SEGA announced that Sonic Rivals, a game exclusively developed for PSP, has shipped to retail stores. Sonic Rivals is a head-to-head competition between Sonic and his top rivals. Gamers can play as one of four different characters from the Sonic Universe, each with separate fast and winding storylines. In addition, the extensive rewards system, which is based on collecting trading cards, allows players to customise their favourite characters. You can connect via wireless to race against a friend, and put trading cards on the line for even more multiplayer challenges.