You must have a GBA, GBA to GCN link cable, two memory card with Chao garden saves, and this game. Send the Chao you want to duplicate to the GBA. It should say it's making a copy. Once you have the copy go to move. Move the duplicated Chao to the Garden in slot two. Now take the Chao out of the garden and put it in slot 1. Now take the other Chao from slot 2 and transfer it to slot 1. You now have two of the same Chao.