PREPARE cake batter and bake as directed on package for 3-L fluted tube pan. Cool in pan 10 min.; invert onto wire rack. Cool cake completely. Transfer to plate.
BEAT dry pudding mix, sugar and milk in medium bowl with whisk 2 min. Stir in Cool Whip. Spread onto cake. Press marshmallows into frosting around bottom of cake. Insert wafers into top of cake as shown in photo. Place 1 animal cracker at base of each wafer.
TOP wafers with 10-inch paper doily for the merry-go-round roof. (See Tip.) Keep refrigerated.