I'm not eligible, because I have burnout-related issues that makes me very flaky about getting things completed.
However, I do have an idea I've mulled around for quite some time, so maybe someone else might get a kick out of it, and maybe get a better idea from it.
The idea started from the fact that the Banshee ultrasonic leak detector also looks a bit like a bathyscape. Now, I personally love to tinker with Linux SBCs, and have built my own enclosures (or rather enclosures' enclosures, silent PCs hidden in furniture and such). I also like the small IPS display panels BuyDisplay sells, because they're okay in quality, but come with sufficient specifications for hobbyists like me to play with. I also like Sci-Fi, of course.
Replace one or two of the ultrasound detectors with a
2.1" round IPS 480x480 display. Use the large inner volume for three lead flywheels running off brushed or brushless RC car motors. Add a sealed lead acid battery, 6V or 12V, in the center; there's room. In the leftover spaces, put one or two solenoids, so that when energized, they knock on the shell, perhaps with a rubber dampener in between. The electrics compartment is large enough for a small SBC, although I'd use separate microcontrollers for each display, connected via USB. Add one or two 6DOF IMUs for sensing when someone moves the enclosure, and maybe a muffled speaker inside it, too.
With suitable software, you have a small Dweller in a exo-bathyscape. It's heavy and hums, but quietly; obviously not just a cheap plastic decoration. Try to rotate it, and it resists the motion in really weird ways. Move it, and the Dweller occasionally knocks about in there, annoyed, and you can maybe see a glimpse of its eye in one of the portholes now and then.
Thö best interactive Halloween decoration, ever, methinks. Probably would have to chain it, though, so it'd be harder to steal.