Pop popcorn using an air popper or neutral oil, transfer to a very large bowl, remove unpopped kernels, prepare greased parchment, and measure candies.

Melt butter over low heat, add marshmallows, and stir constantly 5 to 7 minutes until smooth and glossy without browning.

Remove from heat and stir in vanilla until fully incorporated and fragrant.

Pour marshmallow mixture over popcorn and gently fold from the bottom up until evenly coated.

When mostly coated, add pastel candies or sprinkles and fold lightly to distribute without breaking or bleeding color.

Cool 2 to 3 minutes, grease hands, scoop about 1 cup, and gently press and roll into balls without crushing.

Place on parchment and let set at room temperature 20 to 30 minutes until firm and holding shape.