Preheat oven to 350°F. Prepare baking pans with cupcake liners.
Combine flour, sugar, cocoa powder, baking powder, baking soda, and salt in a stand mixer or large bowl.
Add eggs, one at a time. Stir in milk, oil, and vanilla until well combined.
Stir in boiling water and mix thoroughly.
Pour into baking pans, filling cups 3/4 full. Bake 22-25 minutes. Cool completely before decorating.
Chocolate Frosting
Use a hand mixer or stand mixer to beat room temperature butter until creamy.
Add confectioners sugar, cocoa powder, milk, vanilla, and salt. Beat until frosting is smooth. Add 1tbsp of milk at a time to thin out the frosting, or 1/4 cup confectioners sugar to thicken the frosting until desired consistency.
Decorate Zombie Cupcakes
Cover the cupcake frosting with cookie crumbs. Top with a green zombie hand icing decoration, bone sprinkles, and create blood drips with red gel icing.