Rivermouth

A great curved sword, hiltless. Wavy blue patterns permeate its dark steel. +1 to hit.

Long ago a mighty warrior cut the Bale-Worm Sleeer in two, and a great river sprung forth from the gashed earth. +2 to hit and damage Dragons, Basilisks, and other legless creatures.

Rivermouth speaks in dreams and echos. More than anything, it wants its wielder to change the lay of the land, to reorder the earth in the pattern of heaven.

Second most, it wants to cut slinking things in twain and watch them wriggle in despair.

When you slay a Dragon with Rivermouth, it gains a charge. These may be spent at any time to cast Move Earth, Part Water, or Lower Water.

A Lawful weapon. 9 Intelligence, 8 Egoism.

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In The Caverns of Thracia there is a +2 lawful Red Dragon slaying sword. This is loosely based on a rewrite I did of that sword for a game some years back.

Further Reading: I highly recommend this recent post from Warren D. of I Cast Light!, which provides a table of demands for sentient weapons!