Preheat an oven to 350 degrees Line 36 muffin cups with paper liners.
In a large bowl, whisk together brownie mix, 2 eggs, 1/3 cup vegetable oil, and 1/4 cup water. Stir just until fully incorporated, about 50 strokes; set aside.
In a separate bowl, combine cake mix, 2 tablespoons vegetable oil, 1 1/3 cup water, and 3 egg whites. With an electric mixer beat on low speed until combined. Mix on medium speed for 2 minutes.
Spoon 1 tablespoon brownie batter into 30 prepared muffin cups. Spoon a heaping tablespoon of cake batter over the brownie batter. Spoon 2 tablespoons of cake batter into the remaining 6 muffin cups.
Bake in the preheated oven until golden and the tops spring back when lightly pressed, about 20 minutes. Let cupcakes cool in baking pans placed on wire racks. Frost or pipe with vanilla frosting and decorate with Neapolitan candies.