In a large mixing bowl, add popcorn and candy corn. Melt marshmallows and butter in a medium saucepan until gooey, stirring constantly. Add the vanilla & salt. Pour the melted marshmallow mixture over the popcorn and candy corn. Allow to cool slightly, in order to handle with your hands. When ready to form balls, spray hands with cooking spray and begin forming 2 inch popcorn balls, making sure to mix the popcorn and candy corn well, so that each ball contains both popcorn and candy corn. Press each ball firmly to help compact the ingredients. It may be necessary to stop every once in awhile to wash hands, dry hands and re-spray with cooking spray, if the balls get too sticky. Lay out each popcorn ball onto a baking sheet to air dry for a few minutes. Wrap each ball in saran wrap or store in an airtight container.