I was reminded of this when reading the previous item ... my players were freaked out quite a bit! They finally got the demon, but in another campaign, it could be the stuff of legend, still around, spreading fluff. Go to Comment
A new substance is found in an out of the way area and kept very quiet. It is found to make a perfect counterfeit diamond. Only the most expert of expert appraisers would even have a hope of noticing that it is fake. Only one problem: if it gets wet it starts to slime and if it is saturated, it turns into a glob of gel.