You can't. He's not an unlockable character is SSBB.
You can't.
They are not in the game
Unlock sonic in the subspace emissary and you will get shadow the assist trophy.
Shadow in not a playable character in Super Smash Bros Brawl; he is only an assist trophy.
There is no Shadow in SSBB, but I do believe there are a sticker and trophy of him.
Unlock Sonic
In super smash brothers brawl you cannot unlock shadow. You can only unlock sonic.But you can unlock him in an assist trophy
shadow is not a playable character, but you can find him in an assist trophy.
Shadow is not a character in Super Smash Bros Brawl, unfortunately.
In Super Smash Bros. Brawl you cannot unlock Shadow as a playable character, you can only have him as an assist trophey.
You cannot become shadow in Super Smash Bros. Brawl.
You can't get Shadow on Super Smash Bros Brawl, though you can change Sonic's colour to make him look like Shadow.