Legendary magic weapon (long sword)
Property: You gain a +1 bonus to attack rolls and damage rolls you make with this weapon.
Property: The weapon’s bonus to attack rolls and damage rolls increases to +3. Attacks you make using this weapon ignore resistance to slashing damage. When the number you roll on the d20 for your attack roll using this weapon is 20, make another attack roll against the same target. If you hit again, the target takes an additional 6d8 damage. If the second attack roll is also an unmodified 20 and the target has 150 hit points or fewer, you lop off its head, killing it instantly. If the creature doesn’t have a head, you instead chop the creature in half, with the same lethal result.
This simple long sword is all but indistinguishable from an ordinary weapon. Close examination reveals faint elaborate script running the length of the blade. When a sentient creature notes the script, the creature understands the meaning of the writing. It is a line from an ancient poem describing an epic battle between a young hero and a monstrous beast, which the blade beheaded. In direct sunlight, a vorpal sword gleams with a hard, sharp edge. The blade produces a marked slicing sound as it cuts through the air.