How do you get a shadow chao in sonic adventure 2 battle

You can get a Shadow Chao by making your Chao into a Dark/Running/Running type.

Pet it and feed it with the Dark Characters - Shadow, Eggman, or Rouge to turn it Dark.

The most important part is to give it Green Chaos Drives or animals that raise its Running stat. When it evolves, it should be a Dark/Running type. (This would be its first evolution!).

After your Chao evolves, keep raising its Running. If you notice it will start to look like a Shadow Chao after awhile, then it will be a Dark/Running/Running type.

Hope this helps! :]