Use foil to lift brownies out of pan and invert onto work surface. With 5x2 1/2-inch coffin-shaped cookie cutter, cut 8 coffins from brownies. (Rotate cookie cutter top to bottom and then bottom to top, making cutouts as close together as possible.) Cut each coffin in half horizontally with serrated knife. For each coffin, spread about 2 tablespoons frosting on bottom half of brownie. Arrange 8 bone sprinkles and 1 candy skull on frosting to look like skeleton inside coffin. Outline top of each coffin with white icing. Pipe RIP in center with icing. Place coffin tops, cut sides down and slightly off center, on coffin bottoms.