A longsword made of a strange black metal that gives a very slight rainbow shimmer.
+1 longsword made of an unidentified material
On a critical hit, it will send any extra-planar creature back to it’s plane of origin. It can also be used to summon a low level elemental to assist the wielder once per day.
This sword is a remnant from the time just before the Great Ending, when extra-planar creatures were appearing throughout the region. An adventurer went through one of the portals and returned with ore. There was enough to craft the blade of this sword, which he had then had enchanted to assist in protecting the prime material plane from otherwordly threats.