MICROWAVE chocolate and butter in large bowl on HIGH for 2 min.; stir until melted.
BLEND in sugar: Whisk in water and eggs, one at a time, until well combined. Stir in flour and baking soda; mix until smooth.
FILL 16 large cupcake cups with batter. Bake at 350°F for 25 min. Cool completely.
DECORATE cupcakes as desired, try Santa Claus, Mrs. Claus, reindeer, elves and angels using Cool Whip Topping, icing tubes, mini marshmallows, candy and pretzels.