Preheat oven to 300 degrees F. Line a large rimmed jelly roll sheet with parchment paper.
In an extra large mixing bowl, combine rice cereal, peanuts, pretzels, cheese crackers, and oyster crackers.
Gently toss with large slotted spoons.
Melt butter in microwave and toss together with mixture in bowl.
Combine ranch seasoning powder, mustard powder, grated parmesan, and dried parsley.
Sprinkle over mixture then gently toss together.
Pour mixture evenly over prepared pan.
Bake in oven 30 minutes, tossing mixture halfway through baking.
Allow to cool then store in airtight container.