The Glowing Idol of Rebirth. Crafted from a resurrection scroll and an Ashen Idol of Rebirth, having it in your inventory will resurrect you immediately when you die, and then transform back into an Ashen Idol of Rebirth, so you can charge it up again with another resurrection scroll.
However! Throw it in a backpack, and it will not become Ashen when reviving you. Instead, it stays Glowing, and a ~new~ Ashen Idol of Rebirth in your inventory! Obviously this is a problem, because it will keep reviving you every time you die, rendering the difficulty nonexistant.