Due to any scaling, the animations wpuld reach out longer and the hurt and hix boxes are extended by a certain amount to cope with the model size. At certain sizes, it becomes too hazardas to be playable. So yes, replays will mess up. You just get lucky if your inputs follow up correctly to a certain point.
Well, you can do bone edits and give Mario, Diddy's bones...well, don't follow that advice. I am not too immersed in bone movements and animations for Brawl. Anyway, for a not...stick tail, I curved my Mario's tail to make an "S". It doesn't look bad to be honest. It should be here...somewhere. If not, you can just imagine the tail.
@Kyouma: Is...is that... a machine gun behind her? Where is it sticking?...