Preheat your oven and line a cupcake pan with liners.
In a large bowl, mix the cake mix, box ingredients, pudding mix, and sour cream until smooth and creamy. Fold in the mini chocolate chips for extra chocolatey bites.
Fill each liner about two-thirds full and bake according to the box directions. Let the cupcakes cool completely before frosting.
Beat the butter until fluffy. Add the powdered sugar and cocoa powder, then mix in the vanilla and heavy cream until the frosting is thick, smooth, and easy to spread.
Frost the cupcakes generously and finish with a sprinkle of rainbow candy-coated chips for that classic cosmic look.