I've heard that a lot of SMS games are ports of Game Gear versions, I'm not sure if that applies to Castle of Illusion or not. If I ever come across a copy locally for cheap I'll try it out.
Thank you, that's pretty much my experience with SMS Double Dragon as well. So many people say that the SMS version is better because it's closer to the arcade version and there's no control issues, but I just find it plays badly. I'm not sure if it's due to the controller or if it's actually the game though, I find the SMS controller pretty bad to control in general.