Excalibur

Origin
After The Sword in the Stone broke in Arthur's battle with Pellinore, Merlin is said to have assisted Arthur in retrieving this sword from what is believed to be a Fae named the Lady of the Lake.

After Arthur's death, the sword was returned to the water.

Effects
Excalibur itself has the power to cause wounds that never heal. Its scabbard on the other hand can heal this wounds, and by extension, any wound, external or internal.

However, if the user is dishonest or evil their lungs will fill with water, effectively drowning them.

Appearance
The sword is said to be beautiful in appearance, with a beautiful gem set in the pommel. On the blade is written "take me up" and "cast me away", though these words are faded and barely readable.

The scabbard is equally beautiful, bejeweled and seemingly made of the softest leather.

Collection
Exact circumstances unknown.

Trivia

 * Despite show canon, Excalibur is NOT, and NEVER WAS the Sword in the Stone.