**UPDATE**
I got it. In Scamander’s suitcase is a small ecosystem filled with mythical creatures from the Harry Potter universe. He and Porpentina accidentally switch their cases at a train station and some of the creatures escape into New York. The following disasters give the Salem group the impetus to expose the magical world. So it won’t be just one animal that gets loose it’ll be a whole bunch of them.
**UPDATE**
The Fantastic Beasts movie is looking fantastic and we also learned quite a bit from the trailer about this new world of American wizardry.
There are hints at the basic plot, some nice call backs to the movie series, and some great images to dissect with the utmost care.
Apparently there’s also a Congress of American Wizards headed up by a witch with a really interesting hairdo.

The Magical Congress of the United States of America aka Congress of Silly Hats.
From what we learned in the trailer Porpentina Goldstein portrayed by Katherine Waterson somehow comes into possession of a suitcase filled with magical creatures.
The narration from the trailer makes it seem like the creatures contained within are dangerous, so you have to ask yourself why Porpentina is lugging it around New York. There’s also a chance that the suitcase, or the creature therein, has somehow tied itself to her and she’s unable to let it go.
According to her character biography online she’s previously worked with the Congress, but found herself ostracized from the organization after standing up to her superiors. She’s dressed plainly, so it’s possible that she’s taken a step away from the magical organization or this takes place before her initial employment.

She’s dressed unlike everyone else in the trailer.
It looks as if Porpentina is being confronted by The Magical Congress of the United States of America, but the point at which she either gets captured or goes to them for help isn’t known.
The suitcase is also seen in the possession of Newt Scamander, portrayed by Eddie Redmayne, and who later becomes Porpetina’s husband, but we can’t be sure when she meets him.
The question remains: what’s in the suitcase?
As you may know, Fantastic Beasts and Where to Find Them is a textbook written by Newt Scamander (or by J.K. Rowling) and was published in 1927. The textbook is a detailed account of the magical creatures of the Harry Potter universe that now include beasts found in North America.
There’s a whole list of creatures out there from the Harry Potter universe drawn from the texbook, but there’s nothing stopping the producers of this new film from creating a new beast for this trilogy of films. The other question then of course to ask is if this creature in a suitcase will be following Scamander and Porpentina throughout the films.
There are of course a few possible creatures, but they would have to be docile enough to not harm Scamander and Porpentina, valuable or endangered enough to protect from other wizards, and small enough to fit into a suitcase. It’s also something that the Congress fears for some reason.
It also appears to be very powerful and possibly able to destroy an apartment as seen below. Or perhaps another creature is chasing it a la Attack the Block, or the male creatures tracking down the female creatures.

Clearly not Scamander, maybe a kind of agent of the Congress of some sort investigating.
My first thought was it could be a Boggart, but as we’ve seen in the other films it’s not exactly a creature people want to have around and they’re not especially powerful. It’s never quite said when Boggarts were first discovered, but there are a number of examples of them being found in the early 19th century in London and Scotland. If it was a new creature, you could only imagine the possibilities people could see in something that shape shifts.
It could be a Golden Snidget that were once used as Golden Snitches in Quidditch. It’s an endangered species and is considered extremely rare because of the brutal use of them for the sport. It could be a whole case of them being smuggled into New York that was intercepted by Porpentina who picked up the wrong case at the train station. The chances of it being this little guy is a pretty slim.
Another possibility is a Tebo or Demiguise. These semi-invisible creatures are often used to make protective clothing for wizards. I think that invisibility cloaks have been around for a long time though, so the chances of it being one of these guys is pretty low.
The last possibility is that the suitcase is the creature itself. There’s a possibility of it being a kind of mimic or doppleganger that is carrying its young within. There’s nothing to say that a magical creature can’t be a suitcase, but I guess that feels a little farfetched.

What’s in the box???
Clearly whatever is inside it’s enough to put Scamander and Porpentina on the run from the magic cops.
There’s a scene near to the end of the trailer where Scamander is seen using a disarming spell against an unseen assailant while another character runs with the suitcase.
So they’ll be on the run and probably using all kinds of magic tomfoolery to make sure they escape. At least we know that things end up going pretty well for the duo though as they both lived full lives according to the other books in the Harry Potter universe.

Unincanted spell and some dude holding the case.
***
Speaking of spells there are also a few connections we can drawn from the use of Lumos Maxima at the start of the trailer. The spell is used to create a burst of light and can be used to repel creates like the Gytrash. These magical are aggressive ghostly dogs that perhaps chase Scamander at some point during the film. It’s one of the reasons why he could use the spell.
Another interesting thing to take into consideration is that Albus Dumbledore is actually alive during the film. Born in 1892, Dumbledore would be about 28 years old in the film’s universe. There’s even a chance he could play a role in the film tagging along or at least appearing.
The film also appears it will be dealing with the exposure of the wizarding community in the United States. The New Salem Philanthropic Society is looking to expose the magic world, but apparently they didn’t do a very good job seeing how its still secret in the early 1990s.
Anyway, so there’s still a lot to dissect until the film’s release in November next year. That’s more than 300 days worth of reveals, leaks, and press talks about this new trilogy.
I’m betting on dragons. Perhaps a Norwegian Ridgeback.
Actually, I have a new theory and am writing an update. Think an entire ecosystem filled with mythical animals all in his suitcase. It would give him a great way to study the animals and they could escape too.
That’s an interesting one!