Line a 9" x 13" baking pan with aluminum foil, parchment paper or wax paper. Parchment paper is my favorite. Spray with non stick cooking spray.
Sprinkle 1/3 jar of peanuts on the bottom of the pan.
Melt butter and peanut butter chips over medium heat. Be sure to stir while it melts.
Remove peanut butter mixture from heat. Add sweetened condensed milk. Stir until combined.
Add 1/3 of jar of peanuts and marshmallows. Stir.
Pour over peanuts in baking pan. Spread. Top with remaining 1/3 of peanuts. Add candy corns if you are making scarecrow bars. Press top gently. We don't want the peanuts or candy corns to fall off!