Halloween Oreo Brownie Bars. These Halloween Oreo Brownie Bars are sure to disappear in a hurry at your Halloween party! Loaded with rich chocolate goodness, Halloween Oreos, and sprinkles, this festive treat will make all the little ghouls and goblins squeal with delight! There are actually whole Oreos embedded into the brownies and crushed Oreos sprinkled on top! Tell me that’s not the best thing in the world!