1Heat oven to 350°F. Grease bottom only of 13x9-inch pan with cooking spray or shortening. Make brownies as directed on box for 13x9-inch pan, using water, oil and eggs.
2Bake 23 minutes. Sprinkle with marshmallows; bake 5 minutes longer or until marshmallows are puffed and golden. Sprinkle with candies.
3In small microwavable bowl, microwave chips and shortening uncovered on High 15 seconds; stir. Drizzle over bars. Cool completely, about 1 hour. For easier cutting, use plastic knife dipped in hot water. For bars, cut into 6 rows by 4 rows.