Jumbo and mini cupcakes, held together by marshmallows, are cloaked with fondant to create deliciously creepy ghosts.
Preheat oven to 350. Line 12 cups of a jumbo-muffin tin (each 1-cup capacity) with extra-large cupcake liners. Butter and flour 12 cups of a mini-muffin tin, and tap out excess flour.
Divide batter among muffin tins, filling each cup 1/2 full. Bake, rotating tins halfway through, until testers inserted in centers come out clean, 8 to 9 minutes for mini cupcakes, and 40 to 45 minutes for large cupcakes. Let cool in pans on wire racks. (Cupcakes can be wrapped in plastic, and frozen for up to 1 month; thaw at room temperature before frosting.)
Remove cupcake liners from large cupcakes, trim tops of each cupcake to create a flat surface, and reserve tops for another use. Flip cupcakes over. Spread 1 teaspoon frosting on top of each cupcake. Arrange 3 marshmallow halves on top of each (pictured right), cut sides down, pressing them into frosting. Spread 1 teaspoon frosting over each marshmallow trio.
Trim tops of each mini cupcake to create a flat surface, and reserve tops for another use. Press 1 mini cupcake, cut side down, onto frosting-topped marshmallows.
Spread 1/4 cup frosting over each cupcake stack to create a crumb coat, leaving a 1/4-inch unfrosted rim around bottom. Refrigerate until firm, about 30 minutes.
Divide fondant into 12 equal pieces. On a surface lightly dusted with cornstarch, roll a piece of fondant into a 1/4-inch-thick, 10-inch-wide circle. Center fondant over top of 1 frosted cupcake, smoothing downward and creating ruffles around the bottom. Press candy-coated seeds into soft fondant for eyes, remove, dot with royal icing to secure if desired, and then press seeds into icing. Repeat with remaining fondant, cupcakes, and seeds. Let fondant harden slightly at room temperature before serving.