Gwydion was the last of the magic swords. It was dipped into the Cauldron by High Priestess Oleanna and given to Fionn to overthrow the Daglan. It is described to be as dark and beautiful as the night itself.
It is said by Amren that Gwydion has been gone for millennia, disappeared around the time the last of the Trove went missing. It is the last known Cauldron-Made sword.
Gwydion's power is described as holy, savior's light.