Uh-oh, I rolled a six on the Skull Die, which is the skull. It counts as zero and means I'm due for trouble, regardless of whether I succeed. The rest of the dice total ... exactly 15. Whew. So, in the course of my first attempt to cast this probably ancient spell, I barely manage to keep it from burning out my cortex and instead it burns my enemies. But wait: I rolled the Skull too. The GM lets me know that the thundering ball of fire does indeed incinerate my degenerate foes, but also catches the old chest in the corner of the room, which, being it was actually an incredibly rare sculpture made of highly flammable but valuable material once used by some people who are all dead now, this probable archaeological treasure goes up in flames, destroying it and whatever nifty secrets it may have contained.
I think it's workable.