There's also a chance that a new, original villain could be created for this fanfiction. It could be an alien race that has a grudge against the Doctor for something she did in the past (even if it was a past regeneration). And they target Amy and Rory to get to the Doctor. This new villain could have unique powers and a complex backstory that makes them a formidable foe.
In this fanfiction, it's possible that Amy and Rory will be quite shocked to meet the 13th Doctor at first. They'll soon realize that she has her own unique charm and way of doing things. They could end up helping her save the day, perhaps by using their past experiences to offer different perspectives on the problems they encounter.
The Daleks could be the main villain. They might be trying to manipulate the Doctor's regeneration to create chaos in the time - space continuum. Since the 9th Doctor's unexpected jump to the 11th Doctor disrupts the normal flow, the Daleks could take advantage of this instability to further their evil plans of universal domination.
It could be the Daleks. They are a classic Doctor Who villain. They might see the meeting of two Doctors as a threat to their plans for universal domination and try to stop it.
There are quite a few authors to look for. [Author Name 7] has been writing some amazing 11th Doctor and Rory fanfictions. Their stories are often character - driven, which means they focus a lot on the development of the Doctor and Rory's relationship. [Author Name 8] is another author who is great at world - building within the fanfiction. They create really interesting and believable settings for the Doctor and Rory to explore. And [Author Name 9] has a reputation for writing very humorous fanfictions that still manage to stay true to the characters of the 11th Doctor and Rory.
They could meet during a time-traveling adventure gone wrong, getting stranded in the same era.
It could be Voldemort, of course. He would be a formidable foe, and it would be interesting to see how Amy and Rory's knowledge and skills would help Harry in the fight against him.
One popular storyline is Rory having to save the 11th Doctor from a particularly dangerous alien threat. Maybe the Doctor is trapped in a time - loop created by a malevolent race, and Rory uses his military training and knowledge of the Doctor's habits to break the loop. Another is when they end up in a parallel universe together and have to find their way back home while dealing with the strange and often hostile versions of people they know. And there are also stories where Rory and the Doctor get separated and have to rely on their bond to find each other again.
Maybe during a battle against a common enemy, forcing them to team up. That's when Jack meets 11.
Well, Jack might meet the 11th Doctor when there's a threat to the space-time continuum that requires their combined efforts to fix. Or it could be a chance encounter at a pivotal moment in history.
It's possible that Jack meets the 10th Doctor when they are both drawn to a mysterious energy source. Another scenario could be when they are brought together by a common enemy with a devious plan.