In a medium saucepan melt butter and marshmallows on low heat.
Stirring often until all is melted.
Add peanut butter and stir until smooth.
Remove from heat.
In a large bowl mix the cornflakes, Chex cereal and pretzel bites.
Pour the marshmallow mixture over and stir quickly.
Pour marshmallow mixture into a 8 x8 parchment lined baking pan and spread mixture evenly.
Let sit and then enjoy!