The Set of Caestus of Fingolfin (+10,+10) [5,+20]
+4 dexterity. Provides resistance to acid. Cannot be harmed by acid, electricity, fire, cold. Prevents paralysis.
When aimed, it fires a magical arrow with damage 150. Takes 31 to 60 turns to recharge.
Min Level 40, Max Level 127, Generation chance 7, 4.0 lbs

(Angband 3.1.2v2)