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.
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.
Divide the frosting between 3 medium bowls.
Add a few drops of neon purple gel food coloring to one of the bowls of frosting. Remember, you can always add more coloring, but not remove it! Stir in the food coloring until well combined, and you reach the desired shade. Transfer to a piping bag fitted with a large round piping tip (Wilton 1A) and set it aside.
Add a few drops of neon green gel food coloring to one of the other bowls of frosting. Remember, you can always add more coloring, but not remove it! Stir in the food coloring until well combined, and you reach the desired shade. Transfer to a piping bag fitted with a large round piping tip (Wilton 1A) and set it aside.
Add a few drops each of neon pink and fuchsia gel food coloring to one of the other bowls of frosting. Remember, you can always add more coloring, but not remove it! Stir in the food coloring until well combined, and you reach the desired shade. Transfer to a piping bag fitted with a medium round piping tip (Wilton #8 or #10) and set it aside.
Using the purple frosting, pipe a thick ring around the top of each cooked and cooled cupcake. Fill in the center if required.
Using the green frosting, pipe a slightly smaller ring on the purple layer. Fill in the center if required.
Using the purple frosting again, pipe a slightly smaller ring on the green layer. Fill in the center if required.
Using the green frosting again, pipe a slightly smaller ring on the purple layer. Fill in the center if required.
Using the pink frosting, create thick drips on the top green layer to resemble blood dripping.
Remove the candy eyeballs from any packaging and place one on each frosted cupcake. Enjoy, and Happy Halloween!