Sonic Rivals is a 2006 action Platform Game for the PSP, published by Sega and developed by Backbone Entertainment in 2006 (with a sequel, Sonic Rivals 2, released in 2007). The main objective in these games is to race through each stage and beat your "rival" to the finish line. Stages are broken up by boss fights, where both characters fight against one of Dr. Eggman's robots, with the winner determined by who can land more hits. Sonic, Knuckles, Shadow, Silver and Metal Sonic are playable in the first game, while Tails, Rouge and Espio are added to the playable roster in the second game.