When anything weird happened in Deltarune it's always link to Gaster. In universe he's the one who gave us access to the game soooo I guess it's somehow all his fault.

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When anything weird happened in Deltarune it's always link to Gaster. In universe he's the one who gave us access to the game soooo I guess it's somehow all his fault.
Personally, Gaster's timeline just doesn't click very well with the middle broster assertion (+the point about the skelebros existing ONLY in Deltarune Universe again)
I think if Gaster even was broster, he'd be the eldest one! And like, significantly older too, like ten years-ish!
But still, Deltarune just fully convinces me of dadster being a more likely assertion. I've discussed the idea of Sans and Papyrus being half-humans in this ( x ) post a bit more in debth and I still didn't find any reasons to doubt it since that! Sans bleeding has been a huge smoking gun since the start and we do have an evidence that bleeding is not common for Deltarune Monsters either:
Something I also didn't mention there though is that as far as Deltarunes Chapters went so far (Chapter 5 at the time of writing this post), Papyrus is suspiciously absent and I recently thought that his reclusive behaviour could also do with this!
For example, under half-human assumption Papyrus certainly falls far more on Monster side (save for sometimes showing very normal human eye orbs) but... what if it wasn't always this way?
The commentary about wind in his hair could be a joke, of course, but.. at this rate I just never know with Toby! What if Papyrus DID have hair once and with it, a human body? But the problem with half-Humans half-Monsters would be that falling on the Human side is sort of detrimental. A Monster that can bleed and has above average levels of Determination? Totally acceptable! Heck, Susie is likely candidate! But a Human with a body of dust and magic? Not SO okay.
It IS strange for the kind of person that Papyrus is to be such a shut-in as we've seen in Deltarune... Like, during the Festival as well? Really? So what if unless he is in a heavily magical environment he is basically a sickly Victorian child barely holding onto his life? Moving into Underground with Sans might have helped him to discard the Human side of himself and become a full Monster as it was the only way!
But yeah, with the timeline that put Gaster at odds with the skelebros and possibility that at least one of them is a half-Human I find it more believable that Gaster simply had Sans and Papyrus after going into Deltarune Universe! We don't know how much time he spent in there, but we DO know that he could only find real humans in it because of. well. no "sealed Underground" thing. @sportsballdelight also suggested that Sans and Papyrus were actually children of the Deltarune Gaster who seems to be erased by the Undertale one, and that he could've basically taken skelebros because he was fascinated with their strange crossbreed nature which could also be a variant, as messed up as it is!
One too many eggs
Hating Gaster is a lifestyle (/nm)
According to the Forgotten Man and the Ace copies that Kris created, before the written history Dark and Light Worlds used to be one! The tree is the Card Kingdom's Dark World tree but with Light World's coloration (green) but there are also "normal" grass and bushes, Kris can be in both Light and Dark World forms in this place and the Aces look neither like normal Rudinns neither just revert into cards!
However, everything points towards Gaster being the one that changed the Deltarune world into what he wanted it to be. He wrote the Prophesy, the "grey grass" in Mancountry is literally Gonering creeping in on it and he has issues with Forgotten Man handing Eggs over to them!
The thing about Forgotten Man is very sad, like his vanishment was inevitable and he resisted for as long as he could have, like a ghost that needed to finish his business before finally resting in peace. :( I feel like there is no way he will come back even in the most hopeful ending's case, but he put his faith in Kris.
Worth to mention that Gaster intended to play only with US! Kris, a person with their own will and story and moreover, connection with Forgotten Man and Mancountry, was not in the plans! I think the one that interrupted Gonermaker sequence could be the Knight or even Kris themselves. They do work together either way!
Perhaps, the plan Kris and the Knight have has absolutely everything to do with undoing Gaster's "crime" and setting the world back to its former state and basically? Ralsei's information that if the Knight isn't stopped the Roaring will destroy the world is fear-mongering they got convinced of and could be deconstructed during the story! Heck, Spade King after hearing of the Knight and the Dark Fountains from Jevil started to spread the Darkness and also deeply resented Lightners for casting the Darkners into obscurity! You just know it was not about the kids no longer playing cards because his card got marked, it was about something much more.
I just think that Dark and Light world merging together is not only a type of the ending Toby would probably make considering what stories and themes he enjoys but also... a logical ending? Undoing what Gaster has done after all the set up that he changed the initial, TRUE form of this world for his own experiment!
I'm watching the VHS tapes in the True Lab and completely forgot I named myself Gaster
[>gaste