Keryvian

Keryvian (also known as Foebane or Demron's Bane ) is a Baneblade of Demron and a mighty hand-and-a-half broadsword, or one-handed bastard sword.

Powers
Keryvian is imbued with properties that make its blade magically keen, allow the wielder to jump and fall gently over large distances, and allow the wielder to set a magical proximity alarm. The sword can reflect back magic cast at it or its wielder.

The sword can be commanded to "guard" and will wait until anyone who is not the owner touches it, at which point it will begin attacking this individual and making a very loud singing noise.

The value of the sword as of 1368 DR can be estimated at 35,000 gold pieces.

History
It was once carried by Fflar Starbrow Melruth. As of 1368 DR it was in the ruins of Myth Drannor, but Seiveril Miritar recovered it some time after this and it was residing at Seamist in northern Evermeet where it decorated a wall for a time, until Fflar was resurrected and took up the sword once more.

Keryvian was crafted by the archmage Demron before the fall of Myth Drannor, and is considered the greatest of his series of Baneblades. The blade was used by a thief to kill Demron, hence the name "Demron's Bane". Keryvian's blade glows with a blue fire when drawn, which is light enough to read by, and the hilt bears the likeness of a blue dragon with “teeth” clutching the blade. Only a capable warrior of good heart may take up Keryvian. Like all of the Baneblades of Demron, Keryvian is a powerful magic sword that is imbued with holy energy and that is particularly effective against outsiders, undead, and any evil-aligned creatures, "burning" the life (or unlife) out of them.

In the Baldur's Gate II video games
Keryvian's (Foebane's) full power is only realised when it is combined with Fflar's scabbard, which is also magical. Without it, the sword has a +3 enhancement bonus and does extra damage against all undead, shapeshifters and outsiders. Combining the two isn't simply done, though, and requires special means. With the scabbard, the sword's enhancement bonus rises to +5 and it grants +1 to all saving throws and casts Larloch's minor drain on its target every time it hits.

In Baldur's Gate II: Throne of Bhaal, Foebane can be found on a living statue on the first (uppermost) level of Watcher's Keep, and Cespenar can combine it with its scabbard once that is found.