Take care of your chao using dark characters (Eggman, Rouge, Shadow) rather than using hero characters. Even if you use hero characters, if you pet it a lot with a dark character it'll still turn dark. Dark fruit also help. When it grows up it'll become a dark chao, therefore unlocking the dark garden.
You have to unlock the Chao Garden by collecting the Chao Key in a stage. After you unlock the Chao Garden, there will be two Chao eggs in the garden.
Raise a hero or dark chao to unlock the hero or dark garden.
You've gotta unlock both Hero and Dark Gardens.
unlock him by shagging the boss
There is no breeding garden. Purchase 2 heart fruits from the black market and give one to one chao and one to another.
Actually, you can't...... You just.... can't... If you want to play Sonic Adventure 2 Battle, you'll have to buy the game Sonic Adventure 2 Battle (Not trying to sound stupid by the way.)
There are no minigames for the GBA that you can unlock in Sonic Adventure 2 Battle. You can unlock the boss battles and racing minigames, but they are played on the GC like the rest of the game.
Its already available. To get each mode play through adventure mode and make sure you also set up your chao garden.
Collect emblems
after beating the game 1000times
No
Mostly, but SA2B has upgraded features in the chao garden and a two player Battle mode, as the title implies.