Mournbane

This unique sword is actually a felled branch from the White tree. The tree itself looks and feels like bone, though it is actually plant material. It is an impossibly hard substance, that little except the White Tree, can cut. This sword needs no maintenance, is heavy, and incredibly sharp. It has a special sheath that bubbles out at the edge so that the blades edge does not touch it, as in pervious iterations, the sword has cleaved right through it's own sheath just from dropping it. 
It also has a strange few properties that have been reported over the years, that it increases the potency of healing and resurrection magic. That it alters the flow of time for the wielder, and that the wielder is said to sometimes receive guidance through the sword. Though, it isn't impossible, as the White tree is speculated to be a Sapient being, perhaps even one capable of communicating with the mind.