The Spiral can also be done backwards, with the arms crossing the other way. That is for a clockwise Spiral the arms cross left over right, for a clockwise Reverse Spiral the arms cross right over left.
Begin as you did for the Spiral with a cascade. Instead of making under arm throws, reach over the opposite hand & throw back to the same side, drop the arm that you reach over to get it out of the way. The arms then uncross & the other hand throws an over the top throw that follows the first ball then reaches under to make an Underarm Catch of the first ball.
Backwards feels a little awkward compared to forwards. Instead of making a nice comfortable scoop to throw under the arm you have to carry over the top of the other arm. Carry the ball in a straight line to the opposite side as if slicing across the body. Then throw the ball using a flick of the wrist only.
Again just like a forwards Spiral (so alike in fact that I'm going to use almost the exact same paragraph), every ball is thrown from one side & caught on the other. All the time both hands catch on one side, carry & then throw from the other. One hand will always be moving left & the other always moving right. As you carry keep your arm movements nice & circular, swing back from all the underarm catches with lots of scoop.
Once you can juggle the Spiral backwards & forwards you will be able to pick up Spiral Mess very easily.