Sonic Adventure is a 1998 platform video game for Sega's Dreamcast, and the first mainline Sonic the Hedgehog game to feature three-dimensional (3D) gameplay. The story follows Sonic the Hedgehog, Miles "Tails" Prower, Knuckles the Echidna, Amy Rose, newcomers Big the Cat, and E-102 Gamma, on their quests to collect all seven Chaos Emeralds and stop the series antagonist. Doctor Robotnik to release Chaos, an ancient evil. Controlling one of six characters, each with their own special abilities, players explore a series of themed levels to progress through the story. Sonic Adventure retains many elements from previous Sonic games, such as power-ups and the ring-based health system. Apart from the main game, players can play mini-games like racing and interact with Chao, a virtual pet.
