To make the devil horns, line a cookie sheet or tray with parchment paper or a non-stick baking mat and set it aside. When using fondant, use cornstarch as you would flour when making dough. Dust your work surface, hands, and tools.
Pinch off 2 teaspoons of black fondant and knead it in your hands to make it pliable. Roll it into a cylinder with a thinner point at one end. Curve into a horn shape, pointing upward. Carefully insert a toothpick* into the thick end of the horn. Transfer to the prepared cookie sheet to dry overnight for at least 12 hours. Repeat to make 12 pairs of horns (24 total) plus a few extras.
To make the cupcakes, preheat the oven to 350°F/180°C/Gas 4. Line cupcake pans with 12 black cupcake liners and set them aside.
Using an electric standing or hand mixer, beat the cake mix, eggs, milk, and butter until combined and smooth.
Add black gel food coloring to the cake mix to get a good black hue. Remember, you can always add more coloring, but not remove it!
Use an ice cream scoop to divide the batter between the cupcake liners. Fill about ¾ full.
Bake in the preheated oven for 20 minutes or until an inserted toothpick comes out clean.
Remove the cupcakes from the oven and leave to cool in the pan for 5 minutes before transferring to a wire rack to cool completely before decorating.
To make the frosting, use an electric stand or handheld mixer and add the butter, powdered sugar, cream, and vanilla to the bowl.
Beat on medium speed until creamy, smooth, and stiff peaks form.
Add 6 drops of red gel food coloring and beat into the frosting. Add additional coloring to achieve a blood-red color. Remember, you can always add more coloring, but not remove it!
Transfer the frosting to a large piping bag with a large star tip. You may have to refill the bag as you pipe. Cover any unused frosting with a damp cloth to prevent it from drying out.
To decorate the cakes, pour the sprinkles into a medium shallow bowl and mix to combine.
Pipe a thick ring onto each cupcake and smooth over with a small angled spatula.
Dip each cupcake into the bowl of sprinkles and cover the frosting completely.
Refill the piping bag as required, and pipe red swirls of frosting on top of the sprinkle layer.
Insert a horn on either side of the frosting, pressing the toothpick into the cupcake for stability. Enjoy, and Happy Halloween!