Sonic Adventure 2: is a platform game developed by Sonic Team USA. The game introduces two new playable characters, Shadow the Hedgehog and Rouge the Bat, and is also one of the few Sonic games to officially feature Doctor Eggman as a playable character.

Gameplay: in Sonic Adventure 2 follows the same basic principles of previous games in the series. Along the stages are Rings, that as long as one is retained by the player, he will not lose a life when injured (except during the Miles "Tails" Prower and Doctor Eggman stages, in which the player has a health bar which is reloaded by gathering rings); and also items capsules which, when broken by the character, reward the player with one of a variety of bonuses. These include two different shields — one which simply protects the character from a single hit, and a magnetic one that attracts ring —, a ring bonus, an extra life, temporary invincibility (accompanied with a temporary change in music), a temporary speed boost and destroying nearby enemies. Each character has power-ups which grant them new abilities, such as destroying metal power-up boxes.

Plot: After discovering the existence of a secret weapon mentioned in the diary of his grandfather, Gerald Robotnik, Dr. Eggman infiltrates a high-security G.U.N. facility in search of it. This weapon turns out to be a black hedgehog named Shadow, the self-proclaimed world's ultimate life form. Shadow offers to help Eggman take over the world, and tells him to rendezvous with him at the abandoned Space Colony ARK with more Chaos Emeralds. Sonic is mistaken for Shadow by G.U.N. forces and apprehended, only momentarily evading capture to confront the black hedgehog, who perplexes him with his profound Chaos Emerald-empowered ability to use Chaos Control, which allows him to warp time and space.