Plug the NeoPixels into the Neopixel port on your Hallowing.
Plug the battery into switch, and the switch into the LiPoly battery port.
That's all there is!
The mask will be built in two sections: the bit in front of the lights, and the bit behind the lights.
In front of the lights: The intricate front piece of the mask goes in the very front, stuck to the one-way mirror film.
Behind the lights: The inside of the mask will be made of holographic vinyl. The very back, which will go against your face, is made of soft craft felt.
The NeoPixels will be secured around the edge, facing inwards. The holographic vinyl will reflect the lights, and the one-way mirror will both reflect and let the light through, creating an infinity-mirror effect.
The Hallowing will be mounted between the front and back layers so the TFT screen shows through the window.