Thundercats Season 1 Episode 51

Mumma-ra learns about Excalibur, the greatest sword ever created. He changes into King Arthur, and asks the Lady of the Lake for Excalibur. He meets with the Thundercats, who greet him as a potential ally. Soon "Arthur" challenges Lion-O to a duel, which he foolishly accepts. They will all learn which sword is stronger, the Sword of Omens, or Excalibur.