By collecting keys hidden within levels and reaching the end of a level without getting hit, players can enter special stages. In special stages, players dash across a tube, collecting spheres containing boost power while avoiding obstacles. There are two types of special stages: Bonus Challenge and Emerald Challenge. Bonus Challenges are optional and award the player with extra lives. Emerald Challenges task the player with catching a Chaos Emerald before it disappears. If players collect all seven Emeralds and clear each story, an additional Last Story is unlocked. The Last Story reveals the plot was orchestrated by Metal Sonic, Eggman's top enforcer and a robotic copy of Sonic, in an effort to destroy his namesake. Outside the main game, players can unlock promotional trailers to view and music to listen to. The game also features a split screen multiplayer mode, in which two players can race or battle. Challenges in the multiplayer mode include kart racing and collecting as many rings as possible.