20DID WORSE: THE MARAUDERS
Those who read Rowling's Harry Potter novels know that "Moony, Wormtail, Padfoot, and Prongs," the authors of the Maurader's Map which allowed Harry to track the movements of professors and fellow students in Hogwarts, were the code names of Remus Lupin, Peter Pettigrew, Sirius Black, and James Potter, respectively. This was an important plot detail,
but the films never seemed to bring it up.
In fact, very little time was spent in the films delving into the histories of Harry's dad and his Hogwarts best friends. Fans who solely watched the movies never even learned that Harry's dad could turn into a stag, or that Sirius and Wormtail first acquired the ability to turn into animals to help a teenage Lupin deal with his werewolf transformations. Some details had to be cut for time, but removing the Mauraders so completely was a poor decision.