It was brought to my attention that you can't just drag and drop the Fox Mask Item folder into the Vtube Studio Item folder and expect it to work. With the original uploaded files, you need to import it first as an Avatar and then in the Item menu (single star icon), select "Load current model as Live2D Item."

I have updated the files now, however, so that should hopefully no longer be an issue.

Sorry if anyone was confused by this!