1Heat oven to 350° F (325° F for dark and nonstick pan). Grease or spray 13x9-inch pan.
2Make brownie batter as directed on box, using water, oil, and eggs; stir in 1/2 cup chocolate chips (reserve 1/2 cup). Spread into pan. Bake 24 to 28 minutes or until toothpick inserted 1 inch from edge comes out almost clean. Cool 5 minutes.
3Meanwhile, in medium microwaveable bowl, microwave caramels, butter, and milk uncovered on High 2 to 3 minutes, stirring once, until caramels are melted. Carefully pour and spread over warm brownies. Sprinkle with pretzels, remaining 1/2 cup chocolate chips and toffee bits. Cool completely.