Perhaps they would team up to fight some common enemies. Harry's magic and the Doctor's technology could be a great combination. They might travel through time and space together, with Harry using his magic to assist in situations where the Doctor's technology might not be enough, and vice versa. It would be really exciting to see how their different skills and knowledge would interact.
In this fanfiction, perhaps Harry would introduce the Doctor to the wizarding world. The Doctor could then use his scientific knowledge to understand the magic there, and they might team up to fight some common enemies that threaten both the wizarding world and the universe at large. For example, there could be an alien race that wants to harness the power of magic for their own evil purposes. The Doctor's technology and Harry's magic would make for an interesting combination to combat such a threat.
In this fanfiction, it's Harry, the boy wizard from the magical world of Hogwarts. And then there's the 9th Doctor, a time - traveling alien with his own set of skills and a big blue box called the TARDIS. They are the central figures around which the story would revolve.
Another plotline could be that the immortal has some knowledge that the Doctor needs. The Doctor is constantly seeking knowledge, and the immortal, having lived for so long, might hold the key to solving a big problem in the universe. So the Doctor has to convince the immortal to share that knowledge, which might not be easy as the immortal could be very guarded about it.
Well, they might have some really interesting conversations. The Doctor, with his vast knowledge of the universe, could be intrigued by the immortal's long - lived experiences. Maybe they'd team up to solve some sort of mystery that's been around for ages because of the immortal's long - term perspective and the Doctor's problem - solving skills.
They could also meet in a time - locked situation. The 12th Doctor is trying to solve a mystery from his past, and the 13th Doctor stumbles upon the same situation in her present. At first, they don't understand how they are both involved, but as they start to piece things together, they discover that it's all part of a much larger, more sinister plot. Along the way, they might meet some old friends or foes from their respective tenures as the Doctor. And in the end, they work together to outwit the mastermind behind the plot, all while having some really interesting conversations about their experiences as the Doctor.
In the fanfiction, the 11th doctor, with his eccentric and energetic personality, could initially be a bit confused by the 13th doctor's more modern approach. But then they could start to combine their wits. For example, the 11th doctor's knowledge of ancient alien races could be paired with the 13th doctor's understanding of current galactic politics. They could work together to save a planet that is on the brink of destruction due to a complex web of time - related issues. The encounter could also lead to some humorous moments, like when they argue about who has the better sonic screwdriver or who has had the more exciting adventures.
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.
In fanfiction, when the 13th Doctor meets the 11th Doctor, there could be a lot of chaos and fun. They might exchange stories about their adventures. Maybe they would team up to fight a common enemy that spans across their different timelines.
One possible plot twist could be that they find out they are both parts of a larger plan by an unknown enemy. Maybe an ancient force has been manipulating their timelines to bring them together for some sinister purpose.