Question: What is special about the Gyromite cartridge that you can use it with the Famicom converter?
Gyromite
is a Famicom converter.
It might only be the early prints of Gyromite but they were just a Japanese famicom PCB plugged into a converter, all inside an NES game case. Pictures on Google, I expect.
I'm not interested in Japanese games, mainly because I can't read the language.