- You may be looking for The Beast (The Impossible Planet).
The Great Beast was a counterpart of Irving Braxiatel who lived in an alternate timeline where Gallifrey had embraced magic as a way of life. Once believed to be the planet’s protector, he turned on the people and used magic to become a dragon. He killed this timeline’s version of Leela and hoarded temporal technology.
After falling from the Axis, his N-Space counterpart arrived on this Gallifrey and was made to confront the Great Beast with Narvin. Braxiatel deduced the Beast’s true identity and used the paradox of their meeting to trigger a spark to activate the hoarded technology, incapacitating the Beast. Braxiatel then gave Sir Narvin a hint on where his weakness was likely to be, and Sir Narvin made to attack the Beast. (AUDIO: The Questing Beast [+]Loading...["The Questing Beast (audio story)"])