Generously grease 8" square pan and preheat oven to 350 degrees.
In a large bowl, combine sugar and butter and mix until soft.
Add vanilla and eggs, and mix thoroughly.
Fold in flour, mix well but do not overmix.
Pour enough brownie mix into bottom of pan just to cover the whole bottom.
Sprinkle graham cracker crumbs, mallow pieces, and chopped peanut butter cups over brownie mix.
Completely cover with additional brownie mix.
Spoon peanut butter over brownies and swirl across the top.
Bake until toothpick comes out completely clean, about 35 minutes.