Combine Chex cereals, O's cereal, and peanuts in a medium-sized, microwave-safe bowl then set aside.
Add butter to a small, microwave-safe bowl then microwave until melted, 30 seconds. Add worcestershire sauce, seasoned salt, onion powder, and garlic powder then stir to combine. Pour over dry ingredients then gently fold with a spatula until everything is evenly coated.
Microwave for 45 seconds then stir well. Microwave for 45 seconds two more times, stirring in between, then microwave for an additional 15 seconds (or so) if necessary. Add pretzels then stir to combine, and then spread Chex Mix onto a sheet of wax or parchment paper to cool completely. Store in an airtight container or Ziplock bag.
Notes
Oven-Bake Method: Prepare recipe through step 2 then pour Chex Mix into a baking dish and bake for 30-40 minutes at 250 degrees, stirring every 10 minutes