https://create.arduino.cc/projecthub/dumiloghin/warty-monster-6d44ba
Warty Monster © CC BY
Warty Monster is a “smart” Halloween Pumpkin featuring scary sounds, lights, and cool mist, activated by a proximity sensor and a sonar.

Maker Caleb Lemoine is getting a head start on Halloween with a Raspberry Pi-powered jack-o’-lantern build designed to track visitors’ motions for a spooky surprise: the Pumpkin Pi.

https://github.com/circa10a/pumpkin-pi

In the Harry Potter universe, Professor Moody was, perhaps unfairly, given the nickname Mad Eye for the prosthetic eye he wore. His eye remains a challenge for technically-minded cosplayers aiming to recreate the look and feel of this unique piece of headgear. [cyborgworkshop] had already mastered the basic eye, but wanted to take things further.

The original build relied on a sub-micro servo to move the eyeball. This was done at random as an attempt to simulate the eye’s behaviour in the books and films. However, wanting more, [cyborgworkshop] decided to make the eye more reactive to its surrounding environment. Using the Adafruit Huzzah, a breakout board for the ESP8266, code was whipped up to detect the number of WiFi access points in the area.

https://cyborgworkshop.org/2017/11/19/mad-eye-moody-v2-with-wifi/

Even when you bear a passing resemblance to the paranoid Auror of the Harry Potter universe, you still really need that wonky and wandering prosthetic eye to really sell that Mad-Eye Moody cosplay, and this one is pretty impressive.

Mad Eye Moody – Moving Eyeball Prop
http://www.instructables.com/id/Mad-Eye-Moody-Moving-Eyeball-Prop/

[Super 73] make electric scooters, and they made some Star Wars Speeder Bikes with a twist for Halloween; adding some mirrored panels around the bottoms of the bikes made for a decent visual effect that requires no upkeep or fancy workings. Having amazed everyone with the bikes, they followed them up with a video of the build process.

Halloween Levitating Star Wars Speeder Costume
https://www.youtube.com/watch?v=ikXP1NT_eZA