Okay, there’s a misconception in the fandom about Sans.
Sans, while aware that other timelines exist, does not remember other timelines. He uses equipment in his secret lab to detect when and where other timelines were created or erased. And he can also ‘tell’ when timelines are created by seeing it on Frisk’s face (he can tell how many time he defeated you in no-mercy, and in pacifist he can tell if you came back to talk to him again and calls you a time traveler)
But he cannot actually remembers other timelines, no more than the vague recollection that all characters feel and occasionally reference.
And about his timeline manipulation powers, he can’t manipulate or communicate with other timelines, just the timeline he was in.
I think it might be a little more ambiguous/complicated than this. What you’ve just said is perfectly consistent with the canon information. I actually personally headcanon that Sans doesn’t have direct memories of the different timelines, as I don’t think he would be that hopeful towards Pacifist Frisk if he had lived through the No Mercy run, or that emotionally detached from No Mercy Frisk if he had lived through Pacifist. However, it’s still not clear how much Sans actually knows about these timelines. For example, if you kill Papyrus on any playthrough, in all later playthroughs before a true reset, he will threaten you instead of telling you to watch out for Papyrus’s blue attacks.
This implies that Sans knows, in some timelines that have already happened, that a child with your description killed Papyrus. That’s a pretty specific detail. Perhaps even more telling is how cold Sans is with No Mercy Frisk after they don’t hide behind the convenient lamp, despite the fact he has no direct information that Frisk has killed anyone at this point in time. When Sans sees Frisk walk out the ruins, he acts exactly the same as he normally does, and seems surprised when Frisk doesn’t react to the whoopee cushion, so he probably didn’t know about the destruction of the ruins preemptively. However, he seems to know that some child will only ignore puzzles in bad timelines, which is again, a really specific detail. Sans doesn’t just know timeline’s *exist*, he knows a fair amount of the details that go on in them.
And he knows details of the timeline before you do. During his No Mercy fight, Sans remarks “Seeing what comes next, I can’t afford not to care anymore.” If this is your first No Mercy route, you haven’t gone beyond this point yet, so there’s no way for Sans to “remember” it. Sans’ knowledge of the timelines extends beyond things you, as a player, are actually doing, so it’s plausible he has some degree of knowledge of all *possible* timelines, but not which one he is in at any given time, and not which ones actually occur, nor, I think, which ones have already occured. I think this is a large part of where his hope in Frisk comes from, and why he attempts to stop No Mercy Frisk even when knowing an ending where he dies exists. Because it’s possible those future timelines will never happen.
Now, the secret lab and communicating with other timelines becomes interesting. It’s worth noting that the machine in his lab is broken, so he’s not using that to get reports of the time hops. Notably, he says “our reports show a massive anomaly in the space-time continuum,” implying someone else might be involved. I think it’s pretty likely that the person(s) giving him reports are not from another timeline, but another dimension. This would explain why the picture in Sans’ drawer is of “people you have never met,” instead of a happy timeline, and Sans’ claim that he “knows the feeling” of wanting to go home, as well as his remark “Look, I gave up trying to go back a long time ago. And getting to the surface doesn’t really appeal anymore, either.” Sans’ probably came from another dimension precisely because he knew about the time anomalies in this one (which is probably his job, I assume this is how he gets his money). If Sans is getting reports and money from these people, he likely is still in contact with them. So cross-dimensional communication is probably accurate, cross-timeline maybe not.
In terms of time-travel/dimensional-travel: I don’t think Sans can do that. I think it’s pretty likely that that’s what the broken machine in his lab does, which would explain why he’s here now, and why he can’t get back. I don’t know if this machine ever could have gone through time, but considering it seemed to be used for time policing, I assume it would. And it’s still broken.
But there’s still a lot of ambiguity. I’m not sure how much I believe that Sans is actually just using facial expressions to find your time traveling, especially things like how many times you fought him. Sans is a pretty good bluff, and that is something it makes sense to lie about. So he very plausibly could know more than he lets on, and is lying about it.
The more confusing question is how does Papyrus fit into all of this. Because Papyrus doesn’t appear to be in the picture, nor miss any mysterious home that Sans talks about. I think there are three possible explanations for this: a. Papyrus knows a great deal of this and is better at bluffing than we anticipated, b. Papyrus was a baby whenever the dimension hop occurred, or c. Papyrus is not biologically related to Sans, but a very close found family member. I honestly have no idea which one it is.
I like the idea that he’s just like… Subconsciously aware of timelines.
When I heard “Our reports” I always thought that maybe he had a way to communicate with other Sans’s. Which is sort of evidenced by his “Don’t tell the other Sans’s”. I feel like, somehow, the Sans’s are reporting and sharing information with each other. That’s how he knows these things.
Whoa, when does he say “Don’t tell the other Sans’s?” 😮
He says it if you spare him and come back after he kills you.
Whoa. What’s the context of him saying that? I can’t seem to find any spare-then-fight-him-again videos.
“Well, if you’re back that means we never really were friends. Don’t tell the other Sans’s.”
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