Cut 9 pieces of 7 x 7-inch parchment paper.
Trim excess cake around the skull head if needed. Trim the back side of the skull head to create a levelled surface. Finally, cut the cake in half from top to bottom. Place cake halves on a piece of parchment paper.
Add cream cheese frosting into a piping bag with a large opening and pipe a straight line on the bottom half of the cake. Use a 9-inch angled spatula to spread the filling and leave a 1 cm gap all around the cake. Place the top half of the cake on top of the cream cheese filling.
Use the red buttercream piping bag and pipe buttercream 1x around the cake. Then use a clean angled spatula to spread the buttercream thinly all over the cake. This is called a crumb coat that 'glues' crumbs down and helps seal the filling so that it will not leak while you work. Place the cake into the refrigerator for 10 minutes so that the buttercream can firm up. Repeat this step for the remaining mini cakes.
To decorate, pipe red buttercream 2x around the skull cake (use the parchment paper to help rotate the cake while you pipe). Then use a 9-inch angled spatula to evenly spread the buttercream only around the side of the cake. Smooth the edges around the top sides of the cake.
Use the Oreo buttercream piping bag to pipe on the mask by covering the skull face and leaving a 1 cm gap around the edges. Then use a clean 9-inch angled spatula to smooth out the buttercream.
With a clean fork, lightly puncture even grid marks into the mask to create a 'mesh' look. Clean your fork every so often with a clean paper towel while you puncture.
Pipe a clean line of red buttercream around the edges of the cake and pipe a 'neck' covering where the chin is. Carefully seal the bottom edges with a clean spatula to blend the buttercream and complete the hood look. Smooth out any uneven surfaces with your spatula.
With the melted chocolate piping bag, pipe a horizontal line across the middle of the mask and 2 vertical lines from the chin to the horizontal line in the middle.
Lastly, use the plain buttercream piping bag and pipe on a symbol, then refrigerate the cake. You can create a variation on each mask. For example, 1 mask has a square symbol. The next one has a circle and another has a triangle. Repeat steps #2 - #10 until all the cakes have been filled and decorated. Refrigerate cakes uncovered for 30 minutes for the buttercream to firm up.
To ensure that cakes have a very smooth buttercream finish, you can moisten a clean paper towel with warm water. Rub the paper towel all around a cooled cake (you need to do this while the buttercream is still firm) to smooth out any wrinkles or lines you might have in the buttercream.
Use the melted chocolate bag and pipe a vertical line where the chin is down to the 'neck'. Then draw small lines across the vertical line to create a 'zipper' look for the hood. Place the cake back into the refrigerator.
Buttercream firms up in the refrigerator. When you are ready to serve them, peel off the parchment paper, place cakes out on a platter for 15 minutes at room temperature so that they can soften. Serve and enjoy!