Sounds like a fun project.
I didn't realize the mystic balls were no longer being sold. I had one in the past and it burst in cold storage. I bought another afterwards. It's a blue one that I picked up at Spencer gifts years ago. As described above it does have a pearlescent liquid inside that swirls around. I'm not sure if it moves by a pump or impeller of some sort. After storing for months the glittery particles kind of settles out but will re-disperse after running for awhile.