This is a 4-sided die I designed a while ago and just got around to printing.
I wanted it to look Roman-ish, so apart from using Roman numerals, I've tried to echo elements of Roman architecture in its shape. It seems to roll adequately randomly, from what I've seen so far.
The fin-like structures at the base are some "baked-in" supports that need to be stripped away after printing. I've included them so that the die will print without automatically-generated supports.
I had to enable "Print thin walls" in Cura for my printer, as the support walls are just 0.4mm thick, and with my 0.4mm nozzle Cura wouldn't slice them reliably without that setting enabled.