Excalibur is one of the most powerful magical swords in existence.
Excalibur was a sword created by the most powerful wizard upon Third Earth, the wizard Merlin, for use by King Arthur. Before King Arthur died, he had one of his knights return Excalibur to the Lady of the Lake. There it rested for thousands of years waiting for King Arthur to come and reclaim it. Mumm-Ra once disguised himself as King Arthur to obtain the sword and defeat Lion-O, but was later defeated by Merlin himself. After Mumm-Ra was repelled Merlin offered the sword to Lion-O but he felt he didn't earn the sword himself as he accepted Mumm-Ra's challenge for a unjustly duel. He insisted Merlin return the sword. Respecting Lion-O's decision, Merlin returned Excalibur to the Lady of the Lake, to await someone truly worthy of wielding it's power.
The weapon is possibly the most powerful in existence. It is so powerful that it went toe-to-toe with, and defeated, the Sword of Omens by piercing the Eye of Thundera - the source of its power. It is seen having the ability to shoot energy from the blade as well as red lightning. It also has incredibly powerful magic as shown when it easily restored the Eye of Thundera after Mumm-Ra had destroyed it.
- Excalibur (episode) (first appearance)