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 is one of the traps in the Tomb of Horrors.
In Advanced Dungeons and Dragons, it was a miscellaneous magic item which means you could find it by chance in some dragon's hoard -- 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 Die In a Fire.
In BECMI Dungeons & Dragons, they were quasi-creatures named 'blackballs.' Blackballs are about 5ft in diameter and were one of the few things that Immortals would stay the hell away from. They destroy anything they touch, and act like creatures but never communicate. No Immortal who was vacuumed up by one was never seen again. In theory they're tools or probes from beyond the barrier that keeps the multiverse at only five dimensions, and are sent out to collect items for examination by the barrier-makers.
In Pathfinder the Spheres of Annihilation are the waste generated by the technomagic generators found in the only hive city in the full of undead planet Eox, the Halls of the Living.
The Sphere of Annihilation also exists as a spell in the old, miniature roguelike Larn, where it flies away from the caster, annihilating what it passes over, and bounces off the edges of the dungeon. If you cast two and they collide, they annihilate each other and everthing in a fair-sized circle around them. Even casting just one can easily erase some critical item and make the game unwinnable.