Starfang (5e Equipment)

Weapon (greatsword or longsword), legendary (requires attunement)

Crafted out of a metal that fell from the heavens, the world has possibly never seen its like, or ever will again.

You gain a +3 bonus to attack and damage rolls made with this magic weapon and deal an extra 2d6 radiant damage. When attuned to this weapon, you may select an ability score to increase by 2. You can't increase an ability score above 20. This sword has a critical range of 19-20.
When you attack an object with this magic sword and hit, maximize your weapon damage dice against the target. When you attack a creature with this weapon and roll a 19-20 on the attack roll, that target takes an extra 14 slashing damage. Then roll another d20. If you roll a 20 you lop off one of the target's limbs, with the effect of such loss determined by the DM. If the creature has no limb to sever, you lop off a portion of its body instead.
In addition, you can speak the sword's command word to cause the blade to shed bright light in a 10-foot radius and dim light for an additional 10 feet. Speaking the command word again or sheathing the sword puts out the light.