Author has written 1 story for Harry Potter, and TV X-overs.
Harry Potter is actually the Master and knows he is
Basically, what I'm thinking here is that the Master manages to escape the time lock after getting trapped there. He, of course, regenerates but something goes wrong and he finds himself as an infant with an adult's mind outside of Godric's Hollow. The Potter's biological son died during stillbirth or something and the Master is raised as their son, but he knows that he is a Time Lord. Eventually he ends up in Hogwarts. I would prefer he not be in Slytherin, but it is not a requirement. My reasoning for this is that a truly cunning person would not go into a house where it is expected. What I do not want to see, under any circumstances, is him teaming up with Lord Voldemort. I cannot see that ever happening for the simple reason that Voldemort is an incompetent idiot and the Master doesn't strike me as someone who likes idiots incompetent or otherwise. Whether he decides to get rid of Voldemort himself or not is up to the writer. At some point, I would like to see the Doctor show up.
Harry Potter is raised alongside the Master as siblings
Like the one above, the Master survives or escapes the time lock. In this one, he does not regenerate so much as somehow get reverted back to the infant form of his current regeneration. He gets taken in and is raised alongside Harry Potter. Whether he is thought to be the boy-who-lived or not is up to the author. I would prefer the Master to be older than Harry and to sort of take him under his wing so to speak. Again, I would like the Doctor to pop in at some point and again I do not want to read about the Master joining Lord Voldemort.
The Master and the Doctor at Hogwarts
Through some freak occurrence, the Doctor and the Master are reduced to the childish versions of their current regenerations. They find themselves stranded on earth and are soon accepted into Hogwarts. I don't care when in the Harry Potter timeline they end up in, but I would prefer it to be sometime before the seventh year. Naturally the two find themselves at odds with each other but still banding together against their enemies. They are, after all, a couple of Time Lords, trapped with adolescent teenagers - not the best combination around. Under no circumstances is the Master to join Voldemort; he can consider it, but I don't want him to actually do so. Competent villains don't work well with incompetent morons after all and I would be rather disappointed if the Master didn't make some attempt of taking over the wizarding world at the very least. Whether the Doctor decides to help with the Voldemort issues is up to the author.
Harry Potter is raised by Weeping Angels
I know it sounds odd, but for some reason I would really like to read a fiction where Harry is raised by Weeping Angels. I would like to see the Doctor at some point, but it is not a requirement.
Harry Potter is Jack Harkness
I should think this would be a bit self-explanatory. I don't particularly care whether he attends Hogwarts and then through an accident gets shunted into the 51st century or whether he is raised in that century. Be creative and have fun with this one.
As always, if you decide to use these ideas, please shoot me an email: firstname.lastname@example.org or PM me. I don't particularly care which.