• Begin by preparing the custard filling. In a medium saucepan, combine sweetened condensed milk, whole milk, key lime juice, lime zest, and vanilla pudding mix. Cook over medium-high heat until thickened.
• After it thickens, transfer the filling to a small bowl and cover with plastic wrap, ensuring the wrap touches the custard. Chill in the refrigerator for 3 to 4 hours.

For Cupcakes:

• Puree the mango using a food processor or blender. Preheat your oven to 350°F.
• In a large mixing bowl, combine the coconut cake mix, sugar, and flour.
• Add in the wet ingredients: water, sour cream, vegetable oil, pureed mango, and eggs. Mix on low speed until just combined, then increase to medium-high and beat for 2 minutes.
• Line a cupcake pan with paper liners and fill each liner about two-thirds full with the batter. Reduce the oven temperature to 325°F and bake for 25 to 35 minutes, or until a toothpick inserted in the center comes out clean.
• Allow the cupcakes to cool in the pan for about 10 minutes, then move them to a wire rack to cool completely.

For Frosting:

• In a large bowl, beat together butter, vegetable shortening, vanilla extract, key lime juice, and pureed mango until fluffy, approximately 5 minutes.
• Gradually incorporate powdered sugar while mixing on low speed until the frosting is thick and creamy. Adjust the sugar as desired for texture.
• Once cooled, take a small knife and hollow out the middle of each cupcake.
• Fill each cupcake center with the chilled custard using a piping bag or a resealable plastic bag.
• Using a piping bag, frost the tops of the cupcakes with the mango-lime frosting.
• Finally, decorate with key lime zest, a slice of key lime, and a sprinkle of fun decorations.