Sonic Adventure DX is one of the few games that Metal Sonic is a playable character.
And personally, I think this is the hardest way in a game you have to unlock him.
Now this may seem like a pain in the ass, but if you're one of those people that need 100%, or you just really like metal sonic, then go for it.
After you've earned every single emblem in the game, you got him.
You can only be him on Sonic's stages on trial mode though, much like you can only be super sonic in one stage on story mode. So have at it and expect to have anger issues.
|Metal Sonic||Earn Every Emblem In The Game|
|Super Sonic||Beat All Six Main Character Stories|