8. The Meddling Monk
The Meddling Monk is very much a blast from the past, having fought the first Doctor almost half a century ago. A fellow Timelord named The Monk, he liked to meddle with history and adapt it to his own ends, thus earning him his nickname. While not as popular as The Master in terms of Time Lord opponents, he still has a rich vein of form on the non-canon universe of Doctor Who, having constantly clashed with various incarnations up to the present day. However, if you take it that the last time the Doctor saw The Monk was when he marooned him on an Ice Planet after sabotaging his TARDIS. Again, while hes not in the same league as The Master, it might be a good idea to break out a Timelord opponent for the Doctor, if only because it always seems to offer our eponymous hero an interesting counterpoint to weigh ideals against. Contrasting the Doctors desire to help with the Monks desire for hedonism and manipulation would already be a good idea, but to combine this with the Monks very obvious axe to grind following his banishment and youve already got good fuel for a plot. Also watching Capaldi probably banish him again would be a great way to show off a darker Doctor, if thats the direction Moffat wants to take.