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You may need multiple coats to achieve a glossy coat. Use spray paint in a ventilated area in clothes that you don't mind ruining. Let the box dry completely before bringing the box indoors. Apply the glue directly to the cardboard then attach the craft foam. Applying hot glue directly to foam may burn/warp your craft foam pieces.   Cut and stretch the stockings across the inside of the mouth and hot glue into place. Make sure you can see out of the mouth.
Paint all the craft foam parts. Paint the box. Hot glue all craft foam parts and the battery cover to the box. Use a ruler to draw on the outline of the face with a marker and paint the teeth and tongue. Paste BMO's name onto each side of the box with the O's covering your arm holes. Line the inside of the mouth with black stockings.