What is Shadowslayer?

Shadowslayer is the sword that once belonged to Susannah, and that Jack, Will and Fitch retrieve from behind her gravestone. The sword creates its own light, emerging as though it had been just buried. It has metal which has been folded again and again to give it strength, and inscriptions can be seen in the metal. The sword is one of the Seven Great Blades forged at Raven's Ghyll by a sorcerer named Althis Mac. It is the only sword that still remains.