Preheat oven to 350 degrees (or, the temperature according to the cake box directions) and collect all of your ingredients.
Prepare the cake mix batter and divide evenly into three bowls.
Color one bowl of batter with blue gel food coloring and another with red gel food coloring. Mix until each one is tinted thoroughly.
Alternating between the three colors, fill each section of the muffin pan until they’re about 2/3 full.
Bake according to cake box directions and allow to cool completely.
In a bowl, microwave red candy and coconut oil in 30-second intervals until completely melted (mix the candy between each interval). Line up hard pretzels on a baking sheet, lined with wax paper. Dip each pretzel into melted candy and place gently back on lined baking sheet. Allow the coated pretzels to set completely, at least one hour.
In a large bowl, beat together softened butter, confectioners’ sugar and milk with an electric mixer. Start on low and increase to high - these ingredients combined will make the buttercream frosting.
Once the buttercream is smooth and forms semi-stiff peaks, scoop into a piping bag with Wilton tip #12 attached. Frost each cupcake.
Place 3 blueberries on each cupcake, followed by a pretzel.