BEAT pudding mix and milk in medium bowl with whisk 2 min. Let stand 5 min. Meanwhile, cover bottom of 8-inch square pan with 9 graham squares, overlapping as needed to form even layer.
ADD 2 cups COOL WHIP to pudding; stir gently just until blended. Spread half the pudding mixture over graham squares in pan; top with 9 of the remaining graham squares. Repeat layers.
SPREAD remaining COOL WHIP over dessert. Top with marshmallows.Crush remaining graham square; sprinkle over dessert. Refrigerate 3hours. Drizzle with chocolate syrup before serving.