Starting with a plain black balaclava, I used a craft knife to cut scotchlite/reflective tape into the desired shapes and adhered it to the mask using adhesive tape and steam (and by sewing it where needed).

I sewed one eyehole closed in order to get the desired expression, and partially sewed the other to help make the eyehole smaller. Gemstones and sequins were applied in clusters, using the same method used to adhere the tape.