User blog comment:Cloudthehedgehog12/Super Smash Bros. 4 Ideas/@comment-1945883-20110127013244/@comment-99.179.141.59-20110206183603

Well they are in the DS version, but I see what you mean. Knuckles is thought as more of a main character then Amy though. Cloud probably didn't add her because she doesn't have a significant power and Shadow has many.