Question: how to unlock all characters in sonic advance 3?
Answer: Knuckles the Echidna can be unlocked by completing Sunset Hill (Zone 2), Act 3 with Sonic as team leader. Amy Rose can be unlocked by completing Toy Kingdom (Zone 4), Act 3 with Sonic as team leader. Cream the Rabbit can be unlocked by completing Cyber Track (Zone 6), Act 3 with Sonic as team leader.