Elquillar was a +1 sword whose magical enchantments all revolved around the transformation of appearance. The appearance of the sword, its wielder, and the targets it struck, could all be altered through its various powers.
One major effect that Elquillar possessed was its ability to undo transformation spells, effects, or other abilities upon striking a target, regardless of their origin. Whether it was a renowned archmage transformed into a squirrel or a doppelganger mimicking the appearance of another humanoid, they would revert to their true shape when struck by this weapon.
Furthermore, the wielder of Elquillar could change the form and shape of the sword, into that of a dagger, short sword, scimitar, or other such bladed weapon and could change their own appearance as if they were wearing a hat of disguise. When they actually held the blade in hand, this individual was protected from magic spells and effects as if they were wearing a ring of mind shielding.
This unique sword had quite old, albeit unknown, origins. It was forged some time before the 8th century DR either by elves, in an effort to spy on other races, or, more likely, a particular illusionist from Calimshan known as Akhir Ahad. According to legend, although he long-evaded assassins sent by his political foes, he was eventually caught by night rogues, though not before passing the blade to his most trusted bodyguard. This nameless man bore the blade for some time before it became lost for a few centuries.
Around 300 years later, Elquillar showed up in an auction within the city of Waterdeep, passed hands a number of times, which tied in with a handful of murders, and wound up in the possession of an assassin known as The Rider in White, who primarily killed evil-aligned targets within the region around the Inner Sea.