The Dagger 'Belangil' (3d4) (+16,+14)
+2 dexterity. Branded with frost. Provides resistance to cold. Cannot be harmed by acid, electricity, fire, cold. Slows your metabolism. Speeds regeneration. Grants the ability to see invisible things.
When aimed, it creates a frost ball with damage 50. Takes 6 to 10 turns to recharge.
Min Level 10, Max Level 80, Generation chance 2, 1.2 lbs

(Angband 3.1.2v2)