The Demonhorn of Gothmog [2,+13]
This horn is about six feet long. Just looking at it makes you nervous.

It is from a group of items that once belonged to Gothmog, the High
Captain of the Balrogs
It provides light (radius 2) forever. It decreases your charisma by 5
. It allows you to see invisible monsters. It allows you to sense
the presence of demons. It slows your metabolism. It speeds your
regenerative powers. It can re-curse itself. It cannot be harmed by
acid, cold, lightning or fire.
Level 20, Rarity 0, 3.0 lbs, 500 Gold

(T.o.M.E. 2.3.5)