Blackball

Some call it the deadly sphere: a perfectly black, featureless ball, 5 feet in diameter, floating slowly and soundlessly on aimless courses and unmaking everything in its way. Its origin is unknown, it may not be alive, and it shows no trace of a mind.

Solid or liquid matter it touches simply ceases to exist, with no saving throw, and it moves through anything. No weapon can harm it; even powerful magic blades vanish on contact.

Within 60 feet it senses thinking creatures in every direction, above and below included, and heads for the closest in a straight line, ignoring walls and magical barriers alike. Running is the only answer, and in a maze that may fail. If everyone escapes its 60-foot range, it goes back to wandering.

Anyone who closes in may be chosen (randomly) as its target. Because it is so slow, a Dexterity check, made regardless of initiative and replacing any attack roll, lets the target dodge. Fail, and the victim is erased; anyone who tries to hit it suffers the same fate.

Spells and magic do nothing except a carefully phrased wish, and gate: cast within 60 feet, it pulls the sphere toward and through the opening onto another plane, though whatever the gate summoned may not be pleased.

Ordinary magic items are destroyed by it. A rod of cancellation is ruined but holds the sphere motionless one round (it still erases whatever touches it). Extradimensional spaces such as a portable hole have no effect, yet placing a portable hole inside a bag of holding while the blackball is within 10 feet opens a rift that shunts it to another plane. Colliding with a sphere of annihilation flings it off-plane and wipes out everything else in a 200-foot radius, the sphere too. What happens when it meets an artifact is up to the DM, and probably catastrophic.

Gods can sometimes command one; mortals never can. Luckily they are very rare, and nobody has ever seen two together. The gods suspect blackballs are alive in a strange way. Sages guess that a lone blackball is the leftover of a fiend the gods jailed (doubtful, as it is not evil), that alien minds use them to fetch specimens (doubtful, as victims plainly die), or, the favored view, that they are tools of primordial powers who are to the gods what gods are to mortals.

Destructive but too rare to do more than local damage, they make objects and creatures vanish abruptly, as with disintegrate, except that not a speck of dust or lingering essence is left.