A thought regarding the transition between Sub1 and Sub2. I don't know if I've mentioned this before but I've definitely thought of it in the past.
Note: This assumes that there is a plausible and reasonable explanation for what exactly happens between Sub1 and Sub2 that "fits" with the rest of the universe. Keep in mind that this series wasn't entirely laid out beforehand, so one naturally has to apply things that make sense that weren't in Mat's mind at the time of making the games or knowing where they would end up.
For a while a lot of people thought that Sub1 was effectively being played inside Submachine 2's location, and the player was simply so absorbed in playing the arcade that they had to effectively "wake back up" to the game world. The transition out of the arcade machine seems to simulate them backing up from the screen, so it would support that idea.
What this doesn't address is why they were playing the game in the first place, in the lighthouse dungeon, and where they came from before that. Because even if your protagonist isn't going to be too developed by themselves, there has to be some sort of exposition for their role to work, and the above explanation doesn't provide anything that's substantial enough. In a lot of games, you'll be assigned a role, like being a knight in a village, a school student going about their day, a PhD that accidentally opens up a multidimensional portal during work, something. "Person playing video game in dungeon" without really knowing anything about them isn't an exposition or worthy character profile. I never thought so, at least, which is always why I wanted more information about the player themselves. Why should we care about them? What do they bring to the table? These questions lasted throughout most of the series for me, and I refuse to let them go unanswered because I don't want to play a husk of nothing.
However, I think a lot of that changed with the release of Sub10. It firstly appeared to crumble the narrative that we were actually playing the arcade game from Sub2 in Sub1, given the fact that the basement(s) and the ending area were actually places that we could visit in the games. So that gave rise to the possibility that perhaps those physical locations were where we actually started our journey.
The problem with that, though, is that it still doesn't solve the problem that the first mode of thinking had, with where the player "came from" or who they are. Because there's no reason to accept the player's journey starting in some unknown reason in the basement, without any prior context, either. It's no better than playing the arcade in the dungeon, in my view.
Later down the line after the completion of SubVerse HD, Mat held a Q and A in which he answered a much-longed-for question about the player and their purpose or significance:
Mateusz Skutnik Q36/50 wrote:The purpose is 32. The player is what you want him/her to be. It’s kind of a role-playing element of the Submachine. That person can be just another cog in the machine. Just another explorer of the vast net of Submachine. Or the savior of the world and all structures in it. Depends on you really.
This was initially incredibly frustrating for me, because if I can be a stand-in for the player, then it just basically becomes me inside the Submachine, dropped in at a random location and just going through and escaping like the good little escapist that I guess I was meant to be. No real backstory or anything. I basically turn into that "husk of nothing".
But after a while, my thinking started to change when I thought about how Submachine started out as a single game with no planned series behind it, and how, in that context, and in the context of so many other room escape games, that was all that was expected of you to be. In a lot of room escape games, you are basically yourself, but you just find yourself trapped somewhere that you just need to get out of. This is set up merely for the sake of playing the game. In the game universe, it's okay for this bare-bones explanation to be all that is needed, because that's one of the rules used to make the universe itself.
in conjunction with that I also thought about how it always nagged me that Mat would (and does?) constantly speak to fans in ways that makes it seem like everything he says is said almost "on behalf of" the game worlds he's created. Like speculating about the game as though he's another explorer that knows slightly more than us but still ponders the mystery, or communicating via the titles "Mur" or "Mat". People that really know me know that I've always kind of criticized Mat for doing that, mostly seeing it as cringy or just another gimmick, more or less.
But a lot of that probably comes from my natural tendency to want to put things in nice little boxes (I have a spreadsheet obsession, to an extent, and there's also the Wiki, enough said) so that means to me that the game universe does its thing and our world does its own thing, and melding the boundaries between those two things and introducing that type of gray area is something I don't like, for the reason that it just makes things more complicated. However, my tone on that has changed over time, in part I think due to me having played another game on Steam since the release of the Q and A, that featured a similar sort of metaphysical bridge between the game world and our world, and which really caused me to think about the "validity" of doing such things. (I won't name the game here because it'll effectively immediately spoil it.)
So tying this back to the Sub1/2 transition, my thoughts are instead that Sub1 in fact doesn't really take place in the basements and whatnot that we see in Sub10 either (which would also call into question why so much crap got broken and moss grown in a time frame that I doubt we experienced, unless you want to do time travel theory, which I don't want to do). My current working model is that, given the historical context of Sub1 and how Mat acts, is that it's meant to be a bridge between our world and the game world in a much more meaningful sense than most games would bother to think about. I think, all things considered, it's fine having the first installment be a intentionally murky transition that we experience between our world and the immersion of the game world. Perhaps even though the basement really does exist in the game world, we play through a version of it that slowly transitions us from just playing the escape game to more fully participating in the game universe. There's not a very explainable concrete process behind it, but maybe there doesn't need to be, because this is how Mat is choosing to have the series develop. He wants this bridge to really be strong between the two worlds, because it's what really makes the games special. There's a fine line between role playing and actually having the role-playing underlined and brought into the spotlight, and I think that this second trope is part of Mat's overall gameplan, and I think it ultimately fits.
As far as the actual transition between Sub1 and Sub2, the film that plays at the beginning of Sub2 would then be our thoughts that we are forming right as we're transitioning from our world to assuming the role of the player in the game world. Again, this transition being focused on is what's important. It actually might be one of the best examples of surreal elements found in the Submachine games, especially when coupled with Mat's communication tactics. For me I think I just had to embrace it a bit more to fully appreciate it.
I don't think this explanation is going to make things fully fall in line, but I also don't expect Mat to have crafted a perfect puzzle to put together with the games either, so I'm content with it for now. Hopefully this insight made some sort of sense to people that take the time to read it.
TLDR
Sub1, at the end of the day and given everything we've experienced in Submachine's universe, is best explained as a bridge between our reality and the game reality, and highlights the transition or bridging of these two worlds in a more pointed way that most games that want to immerse you don't really do. Keeping in mind its previous history as an originally standalone game, I think that it's acceptable to see it as a physical manifestation of our transition to being immersed in the game world, which helps explain some discrepancies and questions raised during Sub10 and the bridge between Sub1 and Sub 2.
Edited for grammar and spelling