A video of a pronating cureveball was brought up before. If I'm correct, I may not be, it's very simple. When throwing a normal curveball after the followthrough your middle finger is the first finger to move toward your body. Follow?
With the pronating curveball your pointer finger is the first one to reach your body. Same spin on the ball just the pronating curveball is said to be less stress on your arm. I heard that the real way to throw a curveball is to pronate anyways. That this is nothing new. Everythings the same until release and with the pronating cureveball you roll your hand counter clockwise for a RHP and clockwise for a LHP. Same wrist angle. It's just like pronating with a fastball but you turn your wrist like a curve.
Clear things up?
Someone who knows more about this please check this over and see if it's right.