Pop your Pop Secret Popcorn in the microwave (a bag at a time) according to the instructions on the bag.
While that is happening, heat a large pot on the stove. Drop in your butter and let it melt all the way.
Add the 4 cups of marshmallows (this is generally about 1 standard sized bag of marshmallows) and stir the marshmallows until they are melted and combined with the butter.
Remove the pot from heat and stir the popcorn into the marshmallow mixture. Be sure to keep as many unpopped kernels out of the mix as possible! Stir in the rainbow sprinkles. Eyeball how much you want in the popcorn. It's really hard to put too much in.
Drop large clumps of popcorn onto waxed or parchment paper, allowing the popcorn to cool for a minute or two.
Pick up each popcorn clump and roll into a ball. Makes 8-10 popcorn balls.