Colin Farrell admitted in an interview with CinemaBlend that he took the part of Percival Graves because he deeply loves the Harry Potter franchise and wanted to be a part of it.
Colin Farrell:Work. And the world that it exists within. I mean it's enormous amounts of fun. I have a fucking wand.
Emmi (the voice of the goblin singer in the Blind Pig scene) got the gig via a mysterious email from Abbey Road Studios while she was on holiday (visiting her parents back home). She nearly turned it down because she wanted to chill, but Googled the strange words such as "billywig" and "hippogriff" and said to herself, "Hey, these are Harry Potter terms I'm in!"
Deleted Role: Mildred, Jacob Kowalski's fiancé, was cut from the film.
Deleted Scene: Originally, there was a stinger filmed which showed that Credence had somehow survived and was on a boat leaving America, but it was cut because David Yates felt it was a cheap cliffhanger. Press material for the sequel confirms that the scene is still canon.
All of the actors playing members of the Barebone family, except for Ezra Miller, are from the UK. Samantha Morton (British) plays matriarch Mary Lou, and her adoptive daughters Modesty and Chastity are played by Faith Wood-Blagrove (British) and Jenn Murray (Northern Irish) respectively. Justified with Modesty and Chastity, as all of Mary Lou's children are adopted, though Modesty might be a Double Subversion, since her biological family's former home was in America.
Ireland-born Colin Farrell plays the American Auror Percival Graves.
American Johnny Depp plays the European Gellert Grindelwald.
Ironically, the President of MACUSA herself is portrayed by English actress Carmen Ejogo.
This film introduces the Swooping Evil, a new butterfly-like beast that has never been seen in the Potterverse canon until now. It's a minor Chekhov's Gun.
Much more important to the plot is the Obscurus. An Obscurus is a spiritual force that grows inside the body of a young witch or wizard whose magic is being suppressed by physical or emotional abuse.
I Knew It!: Many fans predicted from a few contextual clues that Grindelwald would be involved in this story, and it turns out that his terrorism is largely responsible for the American government's mistrust of this film's magical, foreign-born hero.
Money, Dear Boy: Despite his fondness for the source material (as mentioned above), Colin Farrell also admitted that he needed the paycheck.
Playing Against Type: Johnny Depp, whose mainstream Hollywood roles are usually heroes, anti-heroes, or tragic villains, plays Gellert Grindelwald, who is almost literally wizard Hitler.
Portmanteau Series Nickname: Not really the series itself, but fans posting what their Hogwarts and Ilvermorny Houses are have started to make up combinations to designate the ones they are in:
Thunderclaw Ravenclaw + Thunderbird
Gryffinbird Gryffindor + Thunderbird
Thunderpuff Hufflepuff + Thunderbird
Puffwudgie Hufflepuff + Pukwudgie
Ravenserpent Ravenclaw and Horned Serpent
Thunderin Slytherin + Thunderbird
Promoted Fanboy: Eddie Redmayne and Ezra Miller. Redmayne in particular has not been quiet about how big a fan he was of the franchise and how he had wanted to be in the original film series. He got his wish at last.
Spoiled by the Merchandise: Averted by the LEGO Dimensions Story Pack based on this movie: While it hit shelves the same day the film hit theaters, the levels didn't become available to download until a day or two later. Also, the last cutscene didn't reveal Graves as Grindelwald until after players downloaded a patch that was put out two weeks after the movie.
Throw It In!: The bit where Newt sticks his wand in his mouth to free his hands was done by Eddie Redmayne as a matter of practicality while doing the scene. Apparently, this led to a "committee meeting" as to whether it "was allowed".
Word of God: Covering an ambiguity the film doesn't explain. Grindelwald uses an advanced form of human Transfiguration to disguise himself as Graves rather than Polyjuice Potion, which is why Newt is able to remove it with a spell.
Word of Saint Paul: Farrell personally believes that Graves was probably at least sympathetic to Grindelwald's cause because he'd worked at MACUSA for a long time. He believes that someone would probably have caught on to the fact that something was off had he randomly started having radically different political beliefs.