HEAT oven to 350°F.
PREPARE cake batter and bake as directed on package for 24 cupcakes, blending dry gelatin mix into batter before spooning into prepared muffin pan cups. Cool cupcakes in pans 10 min.; remove from pans to wire racks. Cool completely.
MEANWHILE, beat pudding mix and mango juice in large bowl with whisk 2 min. (Pudding will be thick.) Refrigerate until ready to use.
USE small sharp knife to cut 1-1/4-inch-wide hole in top of each cupcake, being careful to not cut through to bottom of cake. Fill holes with pudding; cover with removed cupcake pieces. Spread with frosting. Top with mangos just before serving.