Ever roll a die and just KNOW the answer in advance? This die is a foregone conclusion. It's in the shape of a flattened spheroid with a single pip (hole) on the top. The inside of the die is hollow—or rather the top of it is, so it is weighted on the bottom. There are two tiny points around the hole on top to make sure that it isn't stable resting there either.
This version works! Cannot get it to rest anyplace but on its bottom, when printed in Frosted Detail. Might not be so successful in WSF because of how light it is. I'm leaving the metal materials in as options, but I don't know if they can really hollow those out properly, so caveat emptor: it may not work.