I think it's pretty darn rare. It's at least rarer than, say, an Alpha Mission 5 screw, a Donkey Kong 3 screw, or a Gretzky -3, the latter two of which are on this list. I might say it's rarer than a Silent Service 5 screw. There are quite a few copies of this game out there and it's taking some people on here years to find one.