Line bottom and sides of 8-inch square pan with foil or parchment paper. Spray foil with cooking spray. In large bowl, mix cereal, peanuts, chocolate candies and pretzels; set aside.
In large microwavable bowl, microwave brown sugar, corn syrup and butter uncovered on High 2 to 3 minutes, stirring every 30 seconds, until mixture is boiling. Microwave an additional 1 minute allowing mixture to boil and thicken slightly. Let stand 3 minutes to cool slightly.
Pour over cereal mixture in bowl; stir until evenly coated. Using buttered back of spoon, press mixture very firmly in pan. Refrigerate about 1 hour or until firm enough to cut.
For bars, cut into 4 rows by 4 rows. Store covered at room temperature up to 1 week.