Preheat oven to 350°F for metal or glass pans, 325°F for dark or coated pans. Grease sides and bottom of each a 13 x 9 inch pan with shortening. Flour lightly.
Blend dry mix, water, softened butter and eggs in large bowl at low speed until moistened (about 30 seconds).
Beat at medium speed for 2 minutes. Grease and flour a 13x9 inch baking pan. Pour batter into baking pan and bake for 27 - 30 minutes or until a toothpick inserted comes out clean and cake springs back.
Cool in pan on wire rack for 10 minutes. After the cake cools a bit poke holes all over the top of the cake using the handle of a wooden spoon (making sure to go all the way to the bottom). You want the holes to be pretty big so the pudding goes down into the holes
While cake cools prepare pudding. In large bowl add the dry pudding mix and add the 4 cups milk. Using a whisk mix until the pudding is slightly thickened, but pourable (about 2-3 minutes) add the 1/2 cup sweetened condensed milk and mix again.
Pour the pudding mixture over the cake making sure the pudding goes into the holes. Spread the remaining pudding all over the top of the cake using a off set spatula.
Put the cake in the refrigerator until the cake is completely cooled. Once cooled spread the whipped topping all over the top of the cake. Add holiday themed sprinkles or candy and refrigerate until serving. Refrigerate any leftover.