It confuses me that so many people seem to think Sans remembers stuff from previous timelines, when thereâs so much evidence to the contrary. I see art of it all the time and I wonder if we played the same game.
First, there are plenty of indirect hints in his dialogue. Note that when he makes accurate (or less accurate) guesses about previous timelines, he pretty much always indicates that heâs basing them on clues from your behavior. He also requires you to deliver codewords from his previous selves to prove your time-travel capability when heâs pulling his elaborate time-and-space prank on you--you donât need an intermediary to deliver information from yourself if you just remember it.
Second, his actions make no sense if he remembers. For instance, in his boss fight youâve thoroughly convinced him that youâre irredeemable, that youâll never stop consuming timelines, that he fucked up really badly by letting you get this far...If he remembered that, he would attack you on sight in your next loop, without waiting for you to butcher his and everyone elseâs loved ones. It would make zero sense for him to walk up and shake your hand like nothing ever happened.
But forget all that. There are at least three lines, straight from the man himself, that outright tell us that he doesnât get to keep his memories:
1. [if monsterkind gets to the surface,] âweâll just end up right back here, without any memory of it.â Emphasis mine.
2. [after you get dunked on and come back for another round]Â âdid i getcha?â He has to ask because he doesnât remember dunking on you.
3. [in the same post-dunking dialogue] âdonât tell the other sans-es, okay?âÂ
Sans is a brilliant and extraordinarily perceptive person, who already knows time travel is possible from his scientific work and can draw inferences accordingly. But heâs not another Flowey. It would be pretty boring if he were.