In
NetHack, this
amulet reflects beams from
breath weapons,
spells, and
wands when worn. Unlike the majority of the NetHack
amulets, this one cannot be eaten (after
polymorphing into some sort of
metallivore) to permanently gain its effects. You should always be wearing either an amulet of reflection or an
amulet of life saving if possible. You will find either this amulet or a
bag of holding after completing the
Sokoban levels.
Although this amulet confers protection from some of the most dangerous attacks in the game (such as lightning bolts, death rays, and dragon breath), don't get too smug with it. I had a bad and very stupid accident involving this amulet once when I was in the Valley of the Dead (the first level of Gehennom). I was doing quite well with a very low Armor Class (-15 or something) and was hacking away at a mob of nasties, wielding the mighty Stormbringer. As I was completely surrounded by a large number of monsters, I eventually started to get hungry. Being too lazy to reach into my pack for some rations (which would have taken several turns in those circumstances), I prayed to Anhur instead. I got a message:
"Because you are in the Valley of the Dead, Anhur cannot answer your prayers."
Unfortunately, not only was Anhur unable to respond, but Moloch was personally offended by my efforts; he ominously announced my impending demise and blasted me with a lightning bolt from on high. It bounced off due to the amulet of reflection I was wearing. I was pretty relieved, but then...
"Undeterred, Moloch hits you with a wide-angle disintegration ray --more--"
"You fry to a crisp.--more--"
"Do you want your possesions identified? (y/n)"
Oh well. Don't try to pray in Hell, and consider wearing an amulet of life saving instead.