Pop popcorn using an air popper. Place in a very large bowl and remove any unpopped kernels*. Sprinkle jimmies over popcorn.
Melt marshmallows, butter and pumpkin pie spice in a large pot over medium low heat until smooth and completely melted.
Pour over popcorn and sprinkles and stir until all popcorn is coated with marshmallow mixture. Butter one of your hands well.
Using a cookie scoop (mine was 1/3 cup), scoop out popcorn mixture and use your buttered hand to form a popcorn ball around a stick.
Repeat until all the popcorn has been used up, adding more butter to hands if they start to stick. If desired, drizzle with black or orange candy melts and sprinkle with Halloween sprinkles.
Store in airtight container for 2-3 days.
To remove kernels, I use two bowls. Pop the popcorn into one large bowl. Give it a few gentle shakes to let the unpopped kernels settle to the bottom of the bowl. Then, using your hands, take handfuls of the popcorn and move it to the 2nd bowl, removing any hard pieces as you go (they should be mostly at the bottom). Discard unpopped kernels when you get to them at the bottom of the bowl.