Preheat oven to 350°F and line two 12-cup muffin pans with paper liners.

In a large bowl, combine chocolate cake mix with the ingredients listed on the box (typically 3 eggs, 1 cup water, and ½ cup oil). Beat on medium speed for about 2 minutes until smooth and well-blended, scraping down the sides as needed.

Divide the batter among the cupcake liners, filling each about two-thirds full (approximately 3 tablespoons per cup). Gently tap the pans against the counter to release any trapped air bubbles.

Bake for 18-22 minutes, or until the tops spring back when lightly touched and a toothpick inserted in the center comes out clean.

Allow cupcakes to cool in the pans for 5 minutes, then transfer to a wire rack to cool completely for 30-45 minutes.

Divide the vanilla frosting into three separate bowls. Use gel food coloring to tint one bowl green, one blue/teal, and one red.

For best results, chill the colored frosting for about 10 minutes before piping to help it hold its shape better.

Spoon each colored frosting into piping bags fitted with a large open-star tip.

To create monstrous swirls, hold the piping bag vertically above a cupcake and pipe a tall spiral from the outside in, finishing with a small peak at the top.

Press one large candy eyeball into each frosting swirl to create the monster eye effect.

For extra creepiness, use red decorating gel to draw thin squiggles radiating from the eyeball, or press short pieces of red licorice into the frosting to create bloodshot veins.