Amy first came out in Sonic CD, for the Sega Genesis CD thingy- then she disappeared until Sonic Adventure, and has been a main character since. She's fairly useless, with a hammer and inability to go sonic fast, and the hammer doesn't always damage the villians. She a whiney little bitch who stalks Sonic, who wants nothing to do with her, cause she's a diseased slut.
Shadow came out in Sonic Adventure 2, and since then appeared in the next game, Sonic Heroes. He's an interesting character- an evil clone of sonic, made by robotnic, he's black where Sonic is blue. He's also got a pessmistic attitude, and instead of going "Super Sonic", he does this thing called Chaos Control. Don't know much about it.....