Just beat story mode with both the heroes and Babylon rouges.
Shadow - Beat Heroes story
Finish Crisis City to unlock Shadow the Hedgehog's story.
Complete Sonic's Crisis City.
There is no Kayacan the Hedgehog, sounds like a fan character to me
Shadow has been playable in games after his self titled game. He is playable in Sonic the Hedgehog 2006, Mario and Sonic at the Olympic and the Olympic Winter games, Sonic and SEGA Superstar Tennis, Sonic and SEGA All-Star Racing, Sonic Riders, Sonic Riders Zero Gravity and soon to be Sonic Free Riders, Sonic Chronicles the Dark Brotherhood, Sonic and the Black Knight he was playable as Lancelot and Sonic and the Secret Rings in multiplayer.
Shadow the hedgehog, Sonic Riders, Sonic Riders: Zero Gravity, Sonic the hedgehog (2006), Sonic Rivals, Sonic Rivals 2, Mario and Sonic at the Olympic Games, Mario and Sonic at the Winter Olympic games, Sonic and the Secret Rings (multiplayer character) Sonic and the Black Knight (As Lancelot) and soon to be Sonic Colours on DS.
no, but you can unlock knuckles, amy, and cream.
Unlock Sonic
you have to beat the story of sonic, tails or knuckles.
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
Complete the Heroes Story (beat Jet The Hawk in Sand Ruins).