Sega has announced that Sonic the Hedgehog Advance for the Game Boy Advance and Sonic Adventure 2 for the GameCube will interact with one another thanks to the Game Boy Advance link cable. The connection will be utilized to raise small creatures called chao. You will be able to train chao in the Sonic the Hedgehog Advance and then transfer them into the GameCube version of Sonic Adventure 2, where you may use them in races.
The chao are first obtained in the chao garden in Sonic Adventure 2. In order to transfer the chao to Sonic the Hedgehog Advance so they can be trained, you must place them into what Sega is calling a odekake machine. The Chao can then be transferred to chao's petit garden in Sonic the Hedgehog Advance, where they can be trained. Training chao is accomplished by giving them special objects or by petting them. Special chao eggs will be hidden inside chao's petit garden in Sonic the Hedgehog Advance. These eggs can then be transferred to Sonic Adventure 2 for the GameCube, where they can be incubated. Chao will mutate based upon how they are raised.
Sega also announced that Sonic Adventure 2 for the GameCube is now called Sonic Adventure 2 Battle. Sega has added a two-player battle mode to the game, but the details regarding this option have not been disclosed. Sonic the Hedgehog Advance will include a four-player multiplayer mode that will be available with just one cartridge. Sonic Adventure 2 Battle is currently scheduled for release in Japan on December 20. A US release date has yet to be announced.