4. The Valeyard The Trial Of A Time Lord (1986)
The Trial Of A Time Lord arc is technically four stories but its all part of a bigger overall story of the Doctor being put on trial by the Time Lords for breaking the First Law Of Time (not interfering in the affairs of others) with the prosecution being led by the mysterious figure of the Valeyard. The shock of the revelation that hes a future incarnation of the Doctor is long gone and his bargain with the Time Lords that would allow to steal the Doctors remaining regenerations may have been riddled with paradoxes but the Valeyard is still a pretty good villain. The Doctor having to face off against himself is always a good way of showing off his darker side and getting a deeper insight into the character. Plus, nobodys as formidable an enemy as the Doctor himself. Someone who knows him inside out and will immediately know which weak points to strike. Him teaming up with the Dream Lord from Amys Choice would be many a fanboys dream come true. But the biggest reason for the Valeyard to make a comeback is the end of The Ultimate Foe (the last story of The Trial Of A Time Lord arc) which shows that the Valeyard has survived his battle with the Doctor and is masquerading as the keeper of Gallifreys virtual reality the Matrix. Its been twenty-seven years and this cliffhanger still hasnt been picked up on. Come on, BBC. Pull your finger out.