Pop popcorn according to package directions.

Set aside to cool.

In a large pot, melt butter over low heat.

Add marshmallows, and cook, stirring regularly, until melted.

Remove any un-popped kernels from popcorn, and stir popped popcorn into marshmallow mixture.

Add pretzel pieces, and stir in to combine.

Using a 1 cup measuring cup for large popcorn balls or a 1/2 cup measuring cup for small popcorn balls, scoop out popcorn mixture.

Shape into balls. If the mixture sticks to your hands, spray your hands lightly with nonstick cooking spray.

Press M&M's and mini chocolate chips into the outside of the popcorn ball.

Let cool to room temperature before serving.