Master of the Stolen Sunsword Thundarr the Barbarian : Season 2 Episode 6

During a battle with Yando (a supposed wizard with unusual magic), Thundarr is struck by red negative lightning which significantly diminishes the power of his Sunsword. The weapon can be restored at the nearby Pool of Power, but it is stolen by Yando who seeks to have the Sunsword's power for himself.