Preheat the oven to 350 degrees. Add the cupcake liners to the cupcake pan.
Add the cake mix, water, eggs, cocoa, vanilla, and oil to a large mixing bowl and mix well.
Divide among the liners.
Put the pan in the oven and bake for 15-18 minutes or until an inserted toothpick comes out clean.
Let the cupcakes cool in the pan for 30 minutes.
To make the frosting, mix the marshmallow fluff, butter, powdered sugar, vanilla, and liquid in a bowl. Mix on low for 2-3 minutes and then on high for 3-4 minutes.
Add the frosting to a piping bag with a 1A tip.
Put a circle of the frosting on the cupcake, and then add a mini candy cane and mini marshmallows on top.