Preheat oven to 350°F and line a 9x13 inch pan with parchment paper.
Mix graham cracker crumbs with melted butter and press firmly into the bottom of the prepared pan.
Prepare brownie batter according to package directions, stir in chocolate chips, and spread evenly over the graham crust.
Bake for 25 minutes, then remove from oven and scatter mini marshmallows and chopped chocolate over the top.
Return to oven and broil on high for 1 to 2 minutes until marshmallows are golden and puffed, watching closely so they don't burn.
Cool completely before slicing into bars.