A white dragon appears in the original Merlin story. In this episode, Merlin, as a child, explains that the tower keeps falling down because of the two dragons - one red and one white - fighting. The red is supposed to represent Wales and the white England.
Borden (guest star James Callis) has an argument with Gaius (Richard Wilson). Callis previously played a character called Gaius in Battlestar Galactica (2004).
The main guest star James Callis has played Merlin in the TV film Merlin and the Book of Beasts (2009).
John Hurt, voice of The Dragon, has played another character that was supposedly the last of his kind. He also played the War Doctor on Doctor Who. The Doctor also thought he was the last of his kind only to be proven wrong later in the series.