1. Nagini 

No one wanted Nagini in this movie, no one needed Nagini in this movie, and most people are confused as to why she was included at all. A lot of people (myself included) don't understand why Nagini couldn't have just stayed the snake and favorite pet of Lord Voldemort. She was first introduced in the fourth Harry Potter book, "Harry Potter and the Goblet of Fire," and was then killed by Neville Longbottom in the seventh, "Harry Potter and the Deathly Hallows." So why did Rowling reintroduce her, and as a human woman no less?

It seems she is meant to a friend to Credence since they are both people with a magical curse causing them to be outcasts. So even though I didn't like the idea of her character at all, I at least figured she would offer some importance to the plot. That didn't happen. Other than just following Credence around, she did pretty much nothing. And now that Credence has joined Grindelwald what she will do? Many people think her character was an attempt to introduce diversity to the cast and characters, and while that may be true, they could've done a much better job.

TL;DR: Nagini did nothing to promote the plot of this movie so why did she need an entirely new backstory?

2. Professor McGonagall

Everyone loves Professor McGonagall. She was awesome in the movies and even more awesome in the books. She had the best comebacks ever and she was also very powerful, so of course, fans would love a little cameo of her in the new "Fantastic Beasts" movie, right? Wrong. While it's cool to recognize character's names (she does this with a couple of students, such as McLaggen, who would obviously be grandparents of character in the Harry Potter series), it's just frustrating when it doesn't match a previously established timeline.

Professor Minerva McGonagall appears twice in the new film, once in 1927 and again in a flashback to what appears to be the 1910s. McGonagall wasn't teaching at the school, much less even alive, in either of those decades. Pottermore used to note that McGonagall was born in 1935, but that fact was taken down some time ago. Additionally, in "Harry Potter and the Order of the Phoenix" Delores Umbridge asks McGonagall how long she's been teaching at the school. McGonagall replies "thirty-nine years this December;" considering that book took place between 1995 and 1996, that places McGonagall beginning her teaching career between 1956 and 1957.

And before you suggest it could be an ancestor of her's, the script says it Minerva McGonagall and her father (from whom she got her name) was a Muggle.

TL;DR: McGonagall wasn't born until 1935 and didn't start teaching at Hogwarts until the 1950s according to "Harry Potter and the Order of the Phoenix" so there's no way she could've been there during this movie.

3. Credence Barebone's real family 

THIS is the one that really makes everybody angry. At the end of the movie, Credence finds out from Grindelwald that his real family are the Dumbledores and his own brother (camera shows Albus Dumbledore) is trying to destroy him. This makes absolutely no sense.

This baby had to be born in the late 1800s or early 1900s to be Credence's age in 1927. Kendra Dumbledore, the mother to Albus, Aberforth, and Ariana (the three Dumbledore children from the books) died in 1899 just before he daughter and her husband was in Azkaban at the time so there's no way she gave birth to a Dumbledore child. We also know Credence couldn't have the same father and different mother as the other three Dumbledore siblings because Percival Dumbledore died in Azkaban. Now, ignoring those inconsistencies Leta switches her brother with who we now know was a Dumbledore baby. Why were the Dumblesdores going to New York? We know since Dumbledore taught at Hogwarts for years and Aberforth owned the Hog's Head that they stayed in Europe.

Also, since they were on their way to New York in what seems to be the 1900s or 1910s, the other children all would've been older than 15, so where were they? Honestly, I could go on about this one, but I'll save you the reading.

TL;DR: The timeline of when Credence would've been born doesn't match up with the deaths of the Dumbledore parents established in the Harry Potter novels.