you have to beat the story of sonic, tails or knuckles.
Finish Crisis City to unlock Shadow the Hedgehog's story.
Complete Sonic's Crisis City.
no, but you can unlock knuckles, amy, and cream.
Shadow - Beat Heroes story
Unlock Sonic
Shadow is only unlockable as an assist trophy in Brawl. He is unlocked as an assist trophy when you unlock Sonic as a player.
yes sonic is in shadow the hedgehog you meet him on the way
go through some sonic levels, like 3, and you get him, or silver, i don't know.
To unlock that difficulty you must beat the game with every character (sonic, shadow, silver.)
Shadow the hedgehog debuted in Sonic Adventure 2 and was featured in most games since then. He is playable in Sonic Adventure 2, Sonic Heroes, Shadow the Hedgehog, Sonic 06 and several side projects on handhelds.
it's (sonic the hedgehog) and (shadow the hedgehog) and (silver the hedgehog)
Shadow is not a playable character in SSBB but instead open the trophy cases and shadow might come out. Unlock sonic and you get shadow as an assist trophy.