For Aqua's waist capes and making them "scrunchy" looking, it's called gathering. You put in a single stitch (wide, usually the machine set to 0 stitch works). Then with the thread in there, manually pull and gather the material to make it scrunchy. You usually need 3x as much fabric as it would take to be gathered in the correct look. Some require more. So if the width of the final product is 10", you might want to start with 40" wide and bring it down from there after gathering it, and then cut along the top to taper it in if needed. Anyway, after gathering it, you have to sew it (the machine is really the best way to do this so it stays) again with a regular stitch to sew it into place, and don't forget to backtrack at the beginning and ends so it stays in place.