This will be a bit disjointed and more just making connections than an actual theory, since I don't remember a Lot of Dweller's Empty Path, but here's something from Deltarune Chapter 3 that's been on my mind: Man Country
[more under the cut]
The moment we entered this space I immediately thought of two things: 1) "This looks like Temmie's game" 2) "Kris has their lightworld sprite suddenly"
The first thing I'll go into more detail with but Kris suddenly turning into their light world sprite is interesting, especially since after receiving the egg they come out from behind the tree in their dark world sprite again. It's like this in-between place this one.
About the Temmie game though, a friend and I played it together a while back, and though I haven't played the earlier game I have heard of it from said friend so I will try to put what information I remember here. This is what Temmie's game, Dweller's Empty Path looks like:
You will notice the similarities in the colouring right away of course, and the possible allusion to Deltarune with the fountain bit. Deltarune has also alluded to this game before as the little doll behind Seam in the seap is that of the MC from this game, Yoki
Within DEP as well though, there exists a character that walks around different games (Zera, pictures below) who first appeared in a previous game by Temmie, Escaped Chasm (whose MC also appears and is revealed towards the end of DEP, also featured below beside Yoki)
[note: Lonely girl from Escaped Chasm does look different here and seems to have undergone some sort of transformation, see below how Escaped Chasm looks]
Not only are these two games connected though, there's an entire section in DEP where we seem to walk into a completely unrelated adventure being undertaken by a completely different party, a game within a game being played by some other players, you get locked into that adventure once you begin it and must see this strange game through, featuring party members that appear slightly different in their textboxes:
The man behind the tree says to us in Man Country,
"Once upon a time, the whole world looked like this. Do you think so? Really? You believe something so absurd? I'm happy to hear it. Let me continue..." // "Of course not. It's just a story after all. Now, let me continue..."
An entire world that looks just like this, I interpreted this as referencing DEP at that time. And then if you choose "no" he says it's just a story, much like all these other stories within stories alluding to other stories. Between Gaster shattered across time and space, Sans possibly being from the world of Deltarune and getting trapped in the world of Undertale, Lonely girl showing up in DEP, Zera walking around across worlds, Yoki ending up within an unrelated rpg for a section of the game, and the references Deltarune and DEP seem to make to each other, there is a mess of characters leaking out of the bounds of their stories, a cross-narrative complexity that adds to the already complex metanarratives of these games.
Do I think these games are all 100% canon to each other and super related? Idk, they may be, they may plan to make this more obvious, or they may simply not and these are just references. But allusions aren't just neat easter eggs either, they add to the commentary a text provides. And these connections and references are interesting to me for what they say about metanarratives and the idea of "belonging" within a narrative. Which as a theme is of course further reinforced (as others have pointed out) with the gender shenanigans of Man Country (non men are welcome) and Kris going in and out of their light world sprite + the coloured aces that have gotten lost to time and space, like so much else, like the man and Gaster and possibly Temmie's protagonists too. If not narratively these games are still thematically connected and that's something I intend to keep in mind in future analyses of the games (at least from a literary analysis way, because again, in theory-crafting terms it can be seen as 'just a reference' for what that's worth)
Escaped Chasm (on Itch.io here) is about a lonely girl who's shut herself inside her room and lives vicariously through her art. Her parents have gone missing, and a sinister man lurks outside her house. As reality begins to warp and glitch around her, the girl must find the courage to escape her isolation before her world collapses.
this didn't turn out like i wanted it to but oh well. i'll probably draw something different with the same idea
also didn't expect my doodles to get any notes but- hey! would you look at that! there's actually people here!! hello!!! hi!!!! thank god i'm not alone here i was about to go mad