Sonic Adventure is a 3D platform game with action and role-playing elements.[1] Players control one of six anthropomorphic protagonists as they venture to defeat Doctor Robotnik and his robot army, who seek the seven magical Chaos Emeralds and the evil entity Chaos. Six player characters are unlocked as the game progresses, each with their own story and attributes. Sonic the Hedgehog performs a spin dash, homing attack, and light-speed dash; Miles "Tails" Prower flies, swims, and attacks robots using his tails; Knuckles the Echidna glides, climbs walls, and punches; Amy Rose can defeat enemies using her hammer; Big the Cat is slow and carries a fishing rod he can cast; and E-102 Gamma can shoot laser beams.[2][3]
At the start of the game, the player is placed in one of several Adventure Fields, open-ended hub worlds inhabited by advice-giving non-player characters. The player character is guided and instructed by the voice of Tikal the Echidna. Through exploration, the player discovers entrances to levels called Action Stages, some of which must be opened using keys hidden in the Adventure Field.[4]: 141–142 Once the player accesses an Action Stage, they are tasked with a specific objective, which is different for each character.[5] Sonic must reach the level's end like in prior Sonic the Hedgehog games; Tails must reach the end before Sonic; Knuckles must find three hidden shards of the Master Emerald; Amy must solve puzzles and avoid being caught by a robot; Big must fish for his pet frog; and Gamma must fight his way through stages using projectiles as a defense.[3][4]: 140
Some levels include minigames separate from the main story. These feature different styles of gameplay, among them rail shooting, racing, and sandboarding. Some minigames can only be accessed with particular characters. Fulfilling certain objectives allows the player to obtain bonus items. Unlocked minigames and stages the player has completed can be accessed from a Trial Mode on the title screen.[3]
Like previous Sonic the Hedgehog games, players collect golden rings as a form of health: if the player character is in possession of rings when they are hit by an enemy or other hazard, they will survive, but their rings will scatter and blink before disappearing. Canisters containing power-ups such as speed shoes, additional rings, invincibility, and elemental shields are also hidden in levels. In several stages, the player engages Robotnik or Chaos in a boss fight and must deplete the boss's health meter to proceed.[6][7] Each character starts with a limited number of lives, and the player loses a life if the character drowns, gets crushed, or is hit without any rings in their possession. The game ends when the player runs out of lives. Lives can be replenished by collecting 100 rings or a 1-up.[3]
Players may also discover Chao Gardens, hidden, protective environments inhabited by Chao, a virtual pet. Players can hatch, name, and interact with a Chao,[6] and raise the status of their Chao by giving it small animals found by defeating robots. The Dreamcast's handheld Visual Memory Unit (VMU) allows the player to download the minigame Chao Adventure, in which their Chao walks through a course to evolve and improve its skills.[5][8] Evolving one's Chao improves its performance in competitions called Chao Races. Eggs that can produce special types of Chao are hidden throughout the Adventure Fields. Players can earn emblems by playing through Action Stages, searching through the Adventure Fields, or winning Chao Races.[2][9]Each Action Stage has three emblems that can be earned by replaying the stages and fulfilling objectives, such as beating the level within a time limit.[3]
