The Executioner's Sword 'Crisdurian' (4d5) (+18,+19)
Slays evil creatures, undead, orcs, trolls, giants, dragons. Cannot be harmed by acid, electricity, fire, cold. Grants the ability to see invisible things.
Min Level 40, Max Level 127, Generation chance 4, 26.0 lbs

(Angband 3.1.2v2)