Any creature can spend five minutes sharpening a slashing or piercing weapon or piece of ammunition with this small, glowing whetstone. The sharpened item is imbued with a soft radiance only visible upon close inspection.
A sharpened item ignores resistances and immunities to its damage type, and can cut through objects and creatures alike with ease. It deals an extra 2d4 damage of the weapon's type on a hit. If the target is Small or smaller and the attack deals 10 or more damage, a random limb is cut off, reducing the target's speed (if applicable) by an amount appropriate to the number and orientation of that creature's limbs. The same effect applies to a Medium creature if the attack deals 14 or more damage; to a Large creature if the attack deals 18 or more damage; and to a Gargantuan or larger creature if the attack deals 28 or more damage.
On a critical hit, the target must succeed on a DC 18 Constitution saving throw or die instantly as the blade severs it completely in two.
These effects last for 1d4+1 hours, after which a creature must spend another five minutes sharpening a weapon with the whetstone to gain those properties again. The stone cannot sharpen the same weapon more than once, and a creature that uses the stone more than five times must succeed on a DC 15 Wisdom saving throw or take 2d10 psychic damage.
A creature can use its action to smash the stone with a slashing or piercing weapon, destroying the stone and turning the weapon into a +2 Weapon.