A Meteor Rock that was worked without the use of a flame. It has magnetic properties that are deadly to Demons and other supernatural creatures. Gods, of course, are mostly above that sort of stuff, but lesser gods were just as vulnerable to magnetic disturbances and a piece of iron that carries a charge can actually penetrate their defensive field. Steel Jacketed ammunition would be the equivalent these days. Of course with serious Gods it takes something a lot more powerful, like Mithril or Orachalcum. The older and meaner a God gets the tougher they become.