In the spirit of Halloween, I've created a couple of altered books with circuits built into the covers. Glow-in-the-dark polymer clay makes up the eyes, tongues, and teeth. To create the light-up effect, I drilled holes through the eyes, inserted LED bulbs into them from underneath, and then poked the legs through the front covers. I used hot glue to secure the eyes to the tops of the books and to fill in the drill holes.
My first monster model uses a 5V Trinket with a Micro-Lipo Charger soldered to it. The two LEDs are then soldered in parallel to analog pin one. I used Arduino sample code to achieve a creepy fading effect. After completing this circuit, I decided that the use of the charger was overkill, adding more bulk than I wanted.
The second model substitutes a Trinket with 3V logic and a switched JST breakout board. This method is less expensive and more compact.