Newt’s suitcase is bigger on the inside. It’s big enough to live in, even - many of Newt’s creatures do. After a while, Newt does. He adds charms to it bit by bit, step by step at a time, and they layer up and mix and integrate in all sorts of new and interesting ways. Newt doesn’t know what he’s doing, not really (Hogwarts drop out remember?) but he knows enough and he can make up the rest and it all seems to work so why worry? Newt is not the worrying sort.
And then, Newt’s suitcase needs some protections. He likes Tina, Tina is a bro now, but let’s not forget that she closed the lid and sat on his suitcase, picked it up and carted him off to MACUSA like so much laundry in a basket. So, Newt adds some… enhancements. Notice me nots, to begin with, chameleon charms, the usual sort. A few barrier wards - you need a key, now, to open the case (or for Newt, a click of the fingers, but that only works for Newt). And then, his pride and joy, the ability to apparate the suitcase while standing inside it and take everything - case, creatures, all of it - with you, safely out of danger and out of reach of various MACUSA holding cells.
Well. “Apparate”. It’s not quite apparition. It’s disappearing from one place and reappearing in another, and it’s controlled via a runic matrix so huge and complex that he has to roll it up into a giant cylinder and stand it almost directly under the entrance to the case. Except, then, you can’t get in because there’s a giant control cylinder in the way, so he moves things about a bit and shifts the case onto its side so that it’s more like a real door and less like a trap door. It’s different, but it’s all good, even if it takes a while to load up the not-apparition and it makes a funny whooshing sound while it’s working.
Then, then then then, why travel the normal way? Why bother with boats and trains and all of that, why not just move the case? It’s tricky, mapping where he wants to go, and the runes are now unhelpfully rolled away in the cylinder - he’s had to put a barrier round it to keep the creatures out - so he adds all these levers and knobs and twiddly bits and he’s got a control panel going.
He doesn’t always end up where he ought, but he’s close enough. And if he slides about in time a bit, well. The muggles have known about space-time for twenty years now, and he’s usually mostly right. Mostly.
He ends up where he needs to be, and that’s the important thing. He suspects, actually, that his case is interfering a bit here - it’s got so much magic in it now that he wouldn’t be surprised if it’d developed a bit of sentience. He gets in the habit of talking to it as he bustles about, much like he would to any of his other creatures, and it seems to keep the case happy. Why on earth it felt the need to jam the chameleon charms on a phone box of all things though is beyond him, but. It’s still all good.
Then it turns out that “where he needs to be” is at various points “a thousand years in the past” or “two galaxies over” and he runs through space and time (hell of a lot of running involved in this saving-creatures things, which evolves into saving-people things, which somehow become saving-planets and Newt just keeps running) and it’s not all good anymore. It’s friggin awesome.
(And then, just because, Newt drops back into New York in his phone box suitcase. He leans out the door and he holds out his hand and he says, “There’s a whole universe waiting. Come with me?”
The case hums behind him, the slowly spiralling runes of the control column glowing with a faint golden light. The niffler scurries round trying to catch, scuffling paws pressing who knows what buttons and levers that the case carefully puts back behind it. There’s new habitats in the depths of the case, ice tundras where the ood can sing and never be slaves, shadowed forests where the vashta nerada lurk, a pocket of space that stretches impossibly large for when the last space whale in the universe comes to call.
“Come with me?” Newt asks, and Credence takes his hand and steps into the stars.)
(Alternatively: “Come with me?” Newt asks. Graves lifts his coffee and tries to drown himself in it.
“How illegal is that contraption?” he asks from behind his mug.
“It’s perfectly legal!” Newt protests. “They don’t get around to outlawing it until at least the twenty eighth century.”
“The twenty eighth century oh god.”
“On this planet. It might be more illegal on other planets. Maybe.”