Sword of Sharpness
Weapon,
Very Rare
(requires attunement; cost 7000 gp)
Crafting Components
Sharp tooth from a living adult or older dragon
(any sword that deals slashing damage)
Objects hit with this sword take the maximum damage the weapon’s damage dice can deal.
When you use this sword to make an attack against a creature and roll a natural 20, the target takes an extra 4d6 slashing damage. Then roll an additional d20, and on a natural 20 you chop off one of the target’s limbs (or a portion of its body if it has no limbs). The Narrator determines what effect (if any) the result of this severing off is.
You may also speak this sword’s command word to make the blade emit bright light in a 10-foot radius and dim light an additional 10 feet. Repeating the command word or sheathing the sword extinguishes the blade’s light.
Source