For complete animatronics kits, have a look at https://www.bottango.com/pages/kits They are not cheap, but very educational.
You could buy a HalloWing from Adafruit and build something around it: https://www.adafruit.com/product/3900
Many Halloween effects can be done with a simple wiper motor: https://www.youtube.com/channel/UCeBxc0fj-UUayo01ei0B7wQ
Also very popular for instructions: https://www.youtube.com/channel/UCKKBTwYyVYxkpa0_9pqQ13A Steve Koci, the creator, has sadly passed away, but his book "The Ultimate Guide To Do It Yourself Animatronics" might be worth a look.
This is terrific stuff. I love the video from the YouTube channel you posted on overhead animatronic motor. So cool to see how something like this can be built and very accessible.
I remember watching this video (& several others by the same creator) and thinking that I should really get around to doing some of this: https://www.youtube.com/watch?v=Jk3ZsyrTU4M
A few solid starting points for DIY animatronics:
Adafruit + SparkFun: Great for beginner-friendly electronics (servos, sensors, microcontrollers).
Arduino-based Halloween projects on GitHub – lots of open-source code for motion + sound effects.
YouTube channels like Make:, Animatronics How-To, and DIY Creature Workshop often show step-by-step builds.
If you want to go deeper, look into Raspberry Pi-controlled props for more complex movement + audio sync.
For something quick and spooky, even a simple PIR motion sensor + servo motor setup can create a fun jump-scare effect.
My plan is to make a few zombies, one of a zombie child ignoring human flesh while they stare at their phone, and then another zombie teenager stumbling towards a sign that says "YouTube influencer career."
I usually get the Halloween/Fall edition of Make Magazine, which has a ton of projects. They have a selection of them on their site: https://makezine.com/tag/halloween/.
The current issue doesn't seem that Halloweeny, but if you can get the back issues they are fun to have for decor, too.
There’s tons of YouTube videos for Halloween maker stuff. Just search for Halloween maker.
Toby Horrorboy is great:
https://youtube.com/@tobyhorrorboy
Search YouTube for “Furby Hacking”.
Buy some used Fur Real animatronic toys for a few bucks from Facebook marketplace and hack on them with your kids.
Make a spooky UFO scavenger hunt in the park with electronic gadgets.
When we were at Spirit Halloween last week I saw some building blocks like drops and swinging mechanisms for DIY.