In a large microwaveable bowl, mix together cereals, broken pretzels and peanuts. Set aside.
In a small microwaveable bowl, combine brown sugar, butter and corn syrup. Microwave on high for one minute and stir. Then microwave one more minute until melted and smooth. Stir in baking soda until dissolved. Pour over cereal mixture and stir until evenly coated.
Microwave cereal mixture uncovered on high 1 to 2 minutes, stirring and scraping bowl every 30 seconds, just until cereal begins to brown. Pour onto parchment or wax paper and let cool. Break into bite-size pieces and ENJOY!!