For good measure, let's start with a hypothetical. "Describe your muse’s top 3 worst nightmares they have ever dreamed up."
I’m grateful for the word “ever” here because not a lot fazes him as he is now. There was a time that he had a lot more feelings though, and we’re here to exploit that, I guess!
NUMBER 3
It’s no longer a secret to most of us beyond the fourth wall that Sans knows some things. Whether the things he knows are completely forth wall breaking in nature, or the result of some unconventional scientific studies into temporal physics and the nature of reality, we can guess that all of this timeline/anomaly business probably isn’t fully understood or even thought about by a majority of monster-kind.
There’s a good reason he kept his mouth shut about it. He didn’t want to scare anybody, or to make them think he’s some kind of… crazy. What if he drew too much public attention and got labeled a crackpot weirdo comedian trying to pass himself off as a scientist? What if they were right and he was really was crazy to believe in this stuff the whole time?
Unfortunate how things turned out, right?
Nightmare from the past: Insanity
NUMBER 2
If one thing is made incredibly clear by Sans’ dialogue in Undertale, it’s that he loves his brother. Taking into consideration just how much he talks about the guy, one might even think he lives vicariously through Papyrus or something. The two share a rarely maintained, very deep familial bond that allows them to coexist in the same house even through adulthood.
They might argue here and there, Papyrus tossing the occasional playful insult, but they’re just playing around, right? Sans was, and is, confident that if there’s one person he can count on, it’s his brother. He’d never leave, right? He’d never grow to resent him, even if he has gotten difficult and untrustworthy. Even if he loses his patience and yells sometimes…
If that ever stopped being the case, he’d feel very lost as a result. Papyrus is someone he’s always had to fall back on; the one rusty nail keeping Sans pinned to reality that’s never been pulled out, as far as he knows. Imagine taking that out now, when he’s damn near unhinged already.
Nightmare from the present: Abandonment by Papyrus
NUMBER 1
What if you were the only thing standing between some sort of vague demon and the end of your entire world? Sure, there’s some comfort to be found in the vast expanse of nothingness. No thoughts, no feelings and no people means no pain, right? …Or does it?
Sans doesn’t usually remember anything like that happening, but it’s always sitting somewhere in the back of his mind. While it’s part of what keeps him going, some stubborn refusal to give up on his world on the principle of the thing, it’s huge burden as well, and something that still gives him actual nightmares that he doesn’t completely understand.
Flashing blue and yellow, the glint of a knife. There’s this nagging idea in the back of his skull that he’s already failed, somehow… that something vital to him as a person, to his character, if you will, is missing.
Nightmare from the past and the present: The Role of a Judge, and Losing It
