This project is a nice reuse for a cardboard box -- I made mine from the AdaBox 016 shipping box, but any medium corrugated cardboard box will work.
To begin, flatten out your box.
Then, make sure that the LED Matrix display you're using will fit properly.
Sketch out a skull shape on the cardboard, keeping in mind the positioning of the eyes.
To get the positioning of the eyes, plug in the Matrix Portal so you can see the eyes.
Use some tracing paper to trace the sockets, then cut out the sockets and use the paper as a template.
With the hobby knife, carefully cut out the eye sockets from the cardboard.
Create a lower jaw piece with an additional piece of cardboard. This is what the servo will wiggle back and forth.
Poke a hole in the skull's chin for the servo shaft, then screw on a servo horn. This is the part that will rotate, with the separate jaw connected to it.
Cut out some of the skull's lower jaw, leaving behind a few spooky teeth, and cut out some teeth from the lower jaw as well! This will allow light to shine through the silhouette in your window.
Use some double stick adhesive, such as Uglu Squares, to connect the lower jaw to the servo horn.
Hang the Skull
Screw a couple of M3 screws into the threaded inserts on the matrix display and knot some filament or cord to make a hanger for the skull.
You can then hang it from the window casing with a small hook or nail.
Plug it in and enjoy the show!