PREPARE and bake cake mix as directed on package for cupcakes in paper-lined muffin pan. Cool completely.
MEANWHILE, place 2 cups of the marshmallows, chocolate chunks and milk in large saucepan; cook on low heat until marshmallows and chocolate are completely melted and mixture is well blended, stirring constantly. Cool at least 30 minutes. Gently stir in whipped topping.
FROST cupcakes with whipped topping mixture; sprinkle with remaining 2 cups marshmallows and cocoa. Cover. Refrigerate until ready to serve.
Special Extra: Bake cake batter in 13x9-inch baking pan as directed on package. Continue as directed.