2. Grindleward's Path Through Dark Magic
In the final chapters of the series, we were told of Dumbledore's past and his childhood, his siblings and his connection to Gellert Grindelwald. While this answered a lot of questions in relation to Dumbledore, we still know very little about Grindelwald. A film following his path through dark magic and the development of his views on magic and muggles would be fascinating, offering an insight into his life before and after he met Dumbledore and how the chance meeting with the great wizard altered his character. I do not, however, believe that we should be told exactly who killed Ariana. This mystery ensures that at least one thing about Dumbledore is left unanswered, somewhat representing exactly how we have seen Dumbledore since we first met him - a mysterious, intriguing wizard with enough secrets to fill a pensieve. Revealing all of these secrets would remove the layer of mystery and reduce him to being just another wizard. However, we could see Gellert's trip to Godric's Hollow and even the death of Ariana and the effect THAT has on Grindelwald. Again, this idea would work better as a series, offering more chance for the character to develop and for a story to evolve.