A story born of my musings of what Dudley Dursley might have seen during the Dementor attack that gave him the impetus to grow into an adult that stays in contact with Harry Potter after the war. He grew up in a very messed-up family with odd values.
There was a third living being in the maze when Cedric and harry raced for the goblet. Maybe Barty should not have left the goblet with an acromantula.
Harry learns what, exactly, Filch was hired to do.
Where Harry decides that sometimes murder is the best solution.
Sirius learns what happens to dogs caught by Animal Control. Warning: Men may want to avoid reading this.
When Voldemort comes to the Ministry for the prophecy, he is feeling chatty instead of homicidal. (Just a random plot bunny that didn't fit anywhere)
Tom Marvolo Riddle has always had issues with his names... all of them.