Gae Bolga - Cuchulain’s magic spear, also known as the Spear of Light.
The Gae Bolga looked like a bolt of lightning, and returned to his hand when it was thrown. He used it to defeat the Banshee, in both battles with her. When not in use, it reverts to the form of an ordinary stick.
Real World Background
In Irish legend, the Gae Bolga was a magical spear which Cuchulain received from his tutor in arms, the warrior woman Scathach. When hurled at an enemy, it struck him in the stomach, and opened up thirty barbs to increase its damage. The "Spear of Light" appearance of the Gae Bolga in "Gargoyles" may have been inspired by the fact that, in the legends, Cuchulain’s father was Lugh, the god of light.