HOLD UP!
Who is this??
It can't be ruin because no hat! WHO IS IT?!
Wait... COULD IT BE SIN? (Evil Sun)
Yes I call Evil Sun Sin, it rolls off the tongue! BUT IT IT IS WHY IS HE THERE??
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seen from Australia

seen from Bulgaria
seen from Australia
HOLD UP!
Who is this??
It can't be ruin because no hat! WHO IS IT?!
Wait... COULD IT BE SIN? (Evil Sun)
Yes I call Evil Sun Sin, it rolls off the tongue! BUT IT IT IS WHY IS HE THERE??
If the Train gave all the passengers grey jumpsuits before Amelia got involved, and it usually doesn't let you take stuff from the Train home... at what point did it give your stuff back? Did One send a Steward to give your clothes back when you got your Exit? Kez seems to know about the Stewards, but she seemed surprised when it brought gifts. Did it never show up to return Jeremy's stuff? We see him wearing normal clothes in the photo, but that was given to him by Morgan.
Where does the line fall between what you're allowed to keep and not? Jesse doesn't get to take the Apex harpoon pack with him. Lake gets to keep the clothes and the bank pen bracelet, but the handcuffs don't go through. They stay attached until Lake makes it all the way through, even after both arms are already on the other side. The cuffs only disappear after the door closes. The harpoon pack only falls dramatically after the last trace of the glowing doorway has faded away, even though Jesse was still wearing it when Lake last saw him. It almost lets you bring things up until the last second before snatching it back.
The determining factor seems to be if it could be used to prove the Train's existence. Maybe the handcuffs were left behind because they were from the Mirror World, which the Train seems to consider to be under its jurisdiction. It seems to let you keep the clothes on your back, but if the jumpsuits made it though then they could have been used as proof. In that case, would it just spit the passengers out with nothing? The exits seem to work like doorways, so it probably wasn't returning your stuff as you passed through.
Chances are, it lets you keep your outfit within reason. It may be a magical train that kidnaps people and forced them through therapy from hell, but it has STANDARDS! If it looks like something you could find on Earth, then there would be no reason not to let you take it. If its something completely inexplicable like a custom-made harpoon pack, then that has to stay. But some normal looking clothes you stole from an abandoned mall would probably be fair game. It also probably wouldn't let you say, throw a bunch of apples through the open Exit in an attempt to solve world hunger, as amazing as that could be. The Train doesn't care if you starve as a passenger, why would it care if you starve on Earth?
Random stuff in pockets or backpacks might be up for debate. Tulip probably still had the Donut Holer in her backpack, but someone who ran away for months coming back with a pipe for self-defense doesn't seem out of the ordinary. Nobody knows where she was, for all they know she could have needed it. It was confirmed in an AMA that if Jesse's phone had remained un-smashed, then his photos would have ended up blurry and worthless as evidence. It seems important that the Train keeps itself secret under most circumstances. There are reasons it wasn't willing to let Denizens get their own numbers. If everybody knows about the Train, then they won't want to get on.
But when the hell was One planning to give back their clothes? Did Jeremey not have any need for his stuff because Morgan and Kez took such good care of him? Or did One just say "Yoink! This is mine now!" every time someone brought something on board? At what point in the pre-Amelia process were personal belongings dealt with? How many people lost their keys in the process? How many passengers never got their stuff back?
If reflections are alive, how does it work if you're interacting with something in front of a mirror without one?
I see two possibilities:
If you hold something in front of a mirror, it just kind of floats where the reflection would be holding it. Things move exactly as they would if the reflection was still there, it just looks like you're invisible. Would this work both ways? Could a cracked reflection influence the Prime World without leaving the Mirror World? Clothes would have to be an exception to this. Nothing shows up when Tulip walks by the mirror, and Lake's mirror clothes must have been included under the "people can't jump out of people" rule if they had to make wanted posters.
If you pick something up in front of a mirror, the reflected object doesn't move. It's desynced from its Prime World counterpart like a laggy video game. That would definitely start to cause problems for both worlds. Everywhere you go, anything you interact with would get messed up. Just desyncing one thing could cause a butterfly effect that ripples out of control. Just opening a door for someone would leave the mirror world door closed. Reflections would slowly have to subtly break character more often just to make sure they can still do their job. Slowly but surely, your individual impact on the world would start to paint itself on every reflective surface you see.
Seriously, what are the Mirror Medics? Are they a subcategory of Reflection Enforcement? If you join the Flecs, do you get the option of becoming a Medic or an Officer? Are they reflections without Primes like them?
But then when you look at them, just for those few seconds they're onscreen, there are so many differences between them and the Flecs that it seems like they're something else entirely. Their three-fingered hands seem to have joints, and they work like tentacles? They have what appears to be some sort of IV tube thing plugged into their sides? AND THEY HAVE WHEELS? Why do they have wheels?