Vorpal Weapon

5-level Transmutation

You touch a weapon and imbue it with power. Until the spell ends, the weapon becomes indescribably sharp, ignoring resistance to slashing damage, and gains the Siege property, dealing double damage to inanimate objects such as structures. If the weapon has a modifier of less than +3 to attack and damage rolls, its modifier becomes +3 to attack and damage rolls for the duration of the spell.   Additionally, if a critical strike of this weapon would leave a creature with less than 50 hit points, the target creature is decapitated, killing it.