Caladbolg II

Calabold II is a Noble Phantasm use by Archer through Tracing. It should be the demonic sword possessed by the hero of Ireland, Fergus mac Róich; but as the name suggest, it is a different weapon from Fergus's sword, and Archer has applied improvements particular to his usage of it as a Broken Phantasm.

It is a Noble Phantasm considered to be the natural enemy of Cú Chulainn, the great hero of Celtic myth. If the wielder of Caladbolg is Ulster-born, Cú Chulainn has a duty to be defeated once by this sword due to his geas.

The blade of the sword coils into a spiral that can penetrate any target, but it is not specified if this look is due to Archer's modifications for aerodynamic purposes or if the original sword of Fergus already had that aspect.

Source: weapon screen translated by Mirror Moon, and the dictionary resource at Jonnobi.