I just received an Imposter Ditto from the GTS, and it has a Relaxed nature and 31 Speed IVs (I had this confirmed by the Judge in Kiloude City's Pokemon Center). The thing is, when I battle wild Pokemon, I don't always go first. If I understand the Transform mechanics correctly, Imposter copies the wild Pokemon's base stats and nature, but my Ditto's IVs are kept as they are. So in theory I should end up becoming my opponent if they had 31 speed IVs. In which case, shouldn't I always outspeed? Unless they changed it so that my Ditto's nature doesn't change when transforming. I'm not holding any items that slow me down so that's not what's going on.