Attach a USB power supply to a slide dimmer, followed by a wire. The slide dimmer will allow you to control the speed of Nagini while speaking Parseltongue!
Attach a light sensor to your wire, set it to dark mode, and then add another wire to the other end of your light sensor. The light sensor is for your wand later.
Attach a servo to your wire, with the servo attachment shown. Set your servo to swing mode.
Place the servo attachment to the underbelly of the snake, near it's head. Tape around the snake and the attachment. Color the tape to make it more realistic.
Make a lego base to hold your servo in place and hide it and the wires. Test out this circuit to be sure everything is working correctly.
To make a wand, attach your power supply to a button and then a long led light.
Tape a chopstick to the long led light. Color the tape to make it more realistic.
Turn everything on. You will need to use the purple screwdriver to adjust the sensitivity of the light sensor until it works just as you want it to. You are looking for Nagini to move until the light from your wand is near the light sensor; then Nagini should completely stop moving.
Now use your invention! One person will turn Nagini on and control him while speaking Parseltongue and using the slide dimmer. The other will stop him by using whatever spell they like and the circuit wand. Save yourself and impress your friends with your awesome wizarding skills! Stupify!!! (Also, you can build up your lego base to hide your wires even more, and even slip your wires from your wand into your sleeve to hide them!)