Place popcorn in a large mixing bowl. Spray a cookie sheet with cooking spray and set aside.

In a microwave-safe bowl, heat the butter and marshmallows for 3 minutes, stirring halfway through cooking time. Remove from microwave and stir until smooth.

Pour the melted marshmallow over the popcorn. Using a rubber spatula sprayed with cooking spray, stir until popcorn is coated evenly in marshmallow. Spread onto prepared cookie sheet, pressing the mixture down with your rubber spatula.

Sprinkle chopped candy over the top and gently press it into the popcorn. 

When ready to serve, pull apart sections of the popcorn treats, rather than cutting, to create a spider web effect.