In the fight between heroes and villains, will you choose to save the world or conquer it?
The hunt for the Chaos Emeralds is on and battle lines have been drawn between Hero and Dark. Experience two unique adventures featuring both long-time heroes and new and returning villains as they battle for the fate of the world!
Save the day as heroes Sonic, Tails, and Knuckles or cause chaos as Shadow, Dr. Eggman, and Rouge, utilizing each of their unique skills and abilities!
Take a break from the main story and challenge a friend in two-player across kart racing and other competitive modes!
Raise your own pet Chao, improve their statistics, and compete with them in unique mini-games!
Challenge yourself to complete over 150 unique missions across 30 action filled stages!
Storyline
Learning of a secret weapon from the diary of his deceased grandfather, Professor Gerald Robotnik, Eggman infiltrates a high-security G.U.N. facility and revives it using a Chaos Emerald. The weapon – a black hedgehog and self-proclaimed "Ultimate Life Form" named Shadow – offers to help Eggman conquer the world, telling him to rendezvous at an abandoned space colony, ARK, with more Chaos Emeralds. Shadow goes to Central City, encountering G.U.N.'s forces after stealing an Emerald. Shadow has vowed to fulfill a promise to a girl, Maria, which he interprets as one of revenge. Shadow blasts through the military force and meets Sonic. After a brief confrontation, Shadow escapes and G.U.N. captures Sonic, whom they mistake for Shadow.
Meanwhile, Knuckles encounters Rouge and Eggman, who try to steal the Master Emerald. He stops them by shattering the Emerald and searches for the scattered shards. Rouge, spying for the government, heads to Eggman's base and the ARK. There, Shadow shows Eggman the Eclipse Cannon, another superweapon created by Gerald, and discloses his plan: to charge the cannon with Chaos Emeralds and use it to take over the world. Rouge appears, offering them a Chaos Emerald to gain their trust.