Voidsword

First appeared in Siege of Dragonspear, this item can be imported into BG2EE, it's later found at Bodhi's Lair.

In-game description
"Voidsword +3 To all appearances a standard long sword, one standing long in its presence will soon discover it is far more than that. Specially made by Jegg Hillcarver of Bridgefort, this sword has several voidstone shards worked into the metal of the blade. A powerful weapon when used against most targets, its one great deficiency is in its utility against the undead. Objects of the Negative Material Plane have no effect on the unliving; neither then does this blade."