In a medium bowl, beat cake mix, water, oil, and egg whites until smooth. Pour into a greased 9 x 13 baking dish and bake at 350 for 35 minutes. Cool completely.
Poke holes into top of cooled cake. In another bowl, whisk together milk and instant pudding mixes until smooth.
Pour evenly over top of cake. Refrigerate 1 hour.
Scoop frosting into a microwave safe dish and microwave 30 seconds. Pour evenly over pudding.
Top with coconut, M&M's, and frosting decorations. Refrigerate until ready to serve.