Once you’ve cleaned the half skull up completely, make the canvas roughly twice as wide (Image > Canvas Size). Then right-click (Ctrl + click) on the half-skull layer in the Layers palette and select Duplicate Layer from the options. Now use Free Transform on the new layer (Cmd/Ctrl + T) and then right-click (Ctrl + click) on the image of the half-skull, and select Flip Horizontal from the menu options.
Set the layer’s blending mode to Multiply and align the new skull-half with the original to make the complete face. Make a new A4 print of this image.
Merge the two skull layers (Shift + click on both layers then hit Cmd/Ctrl + E). To add depth and fierceness to the skull, draw some flames coming out of his mouth and from behind his head. Again, you only need to do this on one side as we’ll mirror it later. At this point, I also drew some spare flames in case I need them later. Scan and clean up the flames using the same tools as before (the Dodge tool and Levels palette).
Select the flames that come out of the skull’s mouth and behind his head using the Polygonal Lasso tool. Then copy and paste the flames into the skull document and move them into their correct positions. Turn the skull layer’s opacity down to roughly 50%.