Preheat oven to 350 degrees F. Place cupcake liners in a cupcake pan.
In a large mixing bowl, add the cake mix and Sprite Zero. Use a handheld mixer and mix on low for 2 minutes. After that, stir in the chopped marshmallows.
Fill each cupcake liner halfway with the cupcake batter. Bake the cupcakes 19-23 minutes. Let the cupcakes cool completely before decorating them.
Add the cream cheese, powdered sugar, and vanilla extract to a mixing bowl and use a handheld mixer to combine.
Add the cereal portion of the Lucky Charms to a zip-up bag. Use a meat mallet to break it up. You want it to be a crumb like consistency.
Spread the cream cheese frosting over each cupcake. Top the cream cheese frosting with the cereal crumbs. I also added a couple of marshmallows to each cupcake.