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 cupcake. Fill holes with pudding; cover with removed cupcake pieces.
SPOON frosting into medium bowl. Add COOL WHIP; whisk until blended. Spread onto cupcakes. Top with mangos just before serving.