From Sonic Retro
The Chao container (チャオコンテナ) is a level object that appears only in Sonic Adventure 2 and its remake, Sonic Adventure 2: Battle.
The Chao containers serve as the primary way of accessing the game's Chao Gardens, although players who have once unlocked the Chao Garden can access it from the Stage Select screen. This replaces Sonic Adventure's method of visiting Chao Gardens in each Adventure Field. Every stage has three Chao containers in it, with the exception of Green Hill, which only has one. Regardless of the order opened, each Chao container contains the following:
- First Container: Chao Key necessary to visit the Chao Garden after the end of the stage.
- Second Container: One copy of all non-rare small animals found throughout the stage to take to the Chao Garden.
- Third Container: One copy of the stage's designated rare small animal (Legendary category).
It should be noted that if a player dies before opening all three containers, they will only need to open containers they have not already opened to get the contents of the second and third containers; the Chao Key and small animals are both retained even after losing a life. Exiting the level will retain every animal collected, but the Chao Key will be lost.