Sphere of Annihilation
An error in the fabric of space, it's not actually a sphere so much as a missing piece of reality. Anything that touches it is destroyed -- no ashes, no dust, no soul, no afterlife, just GONE. How this destroys whole people and not just the parts that touch, while simultaneously destroying only pieces of ground but not the entire continent at once, we do not know.
Up until 4th Ed, this item was the ultimate "no, fuck YOU!" weapon or trap that DMs would use against player characters that were getting too cocky about having more hit-points than God and being able to survive 20d6 fireballs. Appropriately, it shows up in the Tomb of Horrors with a clue telling heroes they should jump in.
In Advanced Dungeons and Dragons, it was a miscellaneous magic item which means you could find it by chance in some dragon's horde -- if it didn't kill you when you accidentally brushed your hand over it. Magic-Users could move it with the power of their big throbbing brains, and threaten monsters with a black hole the size of your fist that moved about 1 foot per round. In D&D v3, it was 2 feet in diameter, anyone could move it at 10 feet per round with a DC30 check adding your level & Int modifier (doubled if you had the sphere's accompanying talisman). In 4e, it's a standard level 29 trap that does 6d6+10 with 15 ongoing damage.
And this is but a small part of why 4e should DIaF.