Headscratchers / Undertale - Sans

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Sans' backstory

• So Sans has an idea about determination which has been shown to allow one to go back in time through saving, and he seems to be able to utilize it. So (and I'm not sure where this falls in relation to other events like Flowey learning about his ability to save), why didn't he use determination to go back and prevent whatever happened that you learn about in his secret lab?
  • SAV Eing is a very specific form of time travel. You can't just pick any point in time and return to it, you have to go to the last very specific point where you consciously dropped an anchor in the timeline to return to upon something serious happening. If Sans didn't learn about Determination AND consciously SAVE sometime before the event AND consciously NOT SAVE any time after that, well, then, he's out of luck.
  • He doesn't go back because he can't go back. He is aware of saving and resetting, and depending on your actions seems well aware that you're a time traveller, but nothing in the game implies he himself can time travel any longer. The most he can do to either the player or Flowey when things go wrong is to make their life so miserable they reset on their own volition.
    • Assuming his dodging is just regular dodging, some of his attacks feature him seemingly teleporting and behave like Flowey's save states. There are times out of battle where he seems to teleport as well. So it is likely that he still has said abilities. It is just that SAVE trumps those. Beings who can save seemingly can reach beyond timelines. If time travel is like Gaster's determination experiments, then it is just a poor man's save. Note how Sans says nothing matters as if he can't change anything, but Flowey simply got bored because he ran out of different ways to change time on his own.
    • Your use of the words "poor man's save" made me wonder... I remember Sans "bleeding" if you beat him in No Mercy. This can't be blood, and the popular theory is that it's ketchup. But maybe not. Determination allows the Player character to go back in time, right? And we also know that Determination isn't just a trait, but a physical force. So if Determination the Force were related to time-travel, and Alphys was doing experiments with Determination... maybe that's what the red stuff is, and maybe that explains Sans abilities in the final battle? He used it out of desperation (I also note that it looks like he's sweating - could that possibly mean he's melting a little bit like Undyne did?) He isn't able to Reset because he doesn't have enough Determination, but injecting yourself with it would probably have a similar effect (yes, it is scientifically possible to inject directly into bone.)
    • Except Sans would likely begin melting, which is what happened to the Amalgamates in the True Lab. Sans appears to have known some things for awhile, so if he was injected with determination well before the events of the game, he'd be pretty malformed at this point. It's more likely that he has done time-travel through some other method, lost it (if the broken machine in his workshop is anything to go by), and is able to make accurate guesses based on how a person reacts. (Like when Frisk shakes his hand before Sans tells them to, or the look on their face when you've been killed an X amount of times by Sans.)
    • Not saying he did it before the start of the game. He could very well have just done it immediately prior to the fight with Chara/Frisk and all it did was amplify what he could already do.
    • Sans looks a lot different — shorter, less sprawled out — than his brother Papyrus. Maybe he was deformed.
    • There is also a theory that the mysterious W.D. Gaster experimented on Sans when he was very young.
    • Don't forget that the first time Alphys injected Determination into the monsters, nothing happened. It took more and more to make them wake up and then collapse. Determination in small enough quantities isn't enough to kill a monster, and in fact could be good for them — it's just that Alphys kept going when nothing happened, and the consequences are too deadly to go for further experimentation.

Sans' behaviour during Pacifist/Neutral Route

• Playing through the game, Sans seems to be a "judge first, actions later" kind of guy, laid back and not bothered with getting his hands dirty unless absolutely necessary, although it's implied the lazy part is due to his awareness of timelines and how hopeless it is. When you meet him for a second dining session, however, he shows one instance of his dead serious attitude, stating that if it weren't for the promise he made to Toriel, "You'd be dead where you stand."...then casually plays it off as a joke. While it might just be that it seems unlikely, and also seems out of character (especially if you've been playing the Pacifist Route and not killing anyone), It'd be more warranted for him to say that in a No Mercy run, so why go to this extreme? What's the motive for him wanting to get rid you? Granted, he is probably talking about when he first met you so whatever actions you took don't matter and the only thing to think of him killing you is giving Asgore the soul, but that seems quite out of character for him to even bother with.
  • Sans can see different timelines. In the back of his and Papyrus' house is a broken time machine. During a No Mercy run, he clearly states he can see the timelines converging on a point where everything just...disappears. It's an implicit warning of the sort of bad time you'll be in for if you do a No Mercy run later — the first major victim of a No Mercy run is Toriel.
  • Sans is still the kind of guy who tries to be friends with everyone he can, despite how lazy he is. It's not hard to think that he was fine with killing a human to free all the Monsters just because it's a generally good thing for him to do from their perspective at the time. He doesn't personally care about leaving the Underground, so he's fine with keeping Toriel's promise to directly keep her happy. He breaks the promise not because he cares about getting your soul, but because you've become a legitimate threat. The dialogue is just him musing that you owe your life to a random act of kindness Toriel made probably before either of them even met you. The mention of friends he makes in No Mercy isn't about having a good feeling about you, anyone who mentions similar feelings have them due to vague memories from your SAVES and Sans says this regardless of how many times you played. Instead, it's Sans speaking in general terms. That he recognized an oncoming threat so big it would end time itself and identified you as the likely cause, but he was hoping deep down that you were still a person and all you needed was some friends and a little fun to stay on the straight and narrow, so he greets you casually like he does with everyone else.
  • The short answer? Because of your powers. You have the ability to SAVE, and thus the potential of messing around with the timeline however you want. His Genocide dialogue implies that he's terrified of this, and his somewhat nihilistic behavior stems from the fact that even if he did try to do anything, you could just reset everything to scratch — completely if you choose to delete the save file entirely. So he wants you to stop your run and either stop playing the game entirely or reset it and go through a less violent route. On a Neutral/Pacifist run, Sans is still wary of you due to Flowey. On one of the Neutral ending conversations, Flowey says that Sans has caused him his "fair share of resets", meaning that Sans likely has knowledge of him. On a Genocide run, Flowey mentions that he's done everything, from saving everyone to killing everyone. Sans likely thinks you're similarly interested in "doing everything", and even if you never killed anyone at all your first run, it would be only a matter of time before you got bored and/or curious and started killing everyone instead (which is exactly what Flowey did). If he hadn't made that promise, he'd have killed the anomaly while it was still weak. With a level in the single digits and a few weak recovery items, your game would've ended as early as Snowdin. Instead, he's giving you a warning; "I can and WILL kill you if you give me a reason to."
  • Well, the Occam's Razor explanation is that Sans means exactly what his dialogue in this conversation suggests: he has (reluctantly) been looking out for you, because he promised to, and without his intervention you would have run into something that he judged likely to kill you. His following dialogue seems to support this: if Sans at this point isn't sure you're a time traveller, then from his perspective, by definition you haven't run into anything you couldn't handle — because you're still alive. Even so, he very clearly suspects something's up. His line "you haven't died a single time" is outright fishing for a reaction.
  • Sans is also very conscious of his brother's desires. He asks you outright to play around with him for a while to cheer him up. At least part of why he didn't just zap you is probably so that Papyrus can get the satisfaction of capturing a human and delivering them to Undyne, who Sans knows could probably kill one if she tried. He doesn't threaten you until you're on your way to confront Asgore directly, who, despite being a boss monster, is "a big fuzzy pushover."

Sans Forgot About His Powers?

• So when you fight Sans in the No Mercy route, he has an unstoppable guaranteed-to-kill-you attack that he only uses when you "Spare" him. But the thing is... why doesn't he just use this attack whenever he wants? Sure, from a gameplay perspective, it wouldn't be very 'fair', but pretty much the whole point of the fight is that Sans is trying to frustrate you into quitting the game, so wouldn't it actually make sense for him to mix in a One-Hit Kill attack with his regular patterns at complete random? For that matter, why doesn't he just use it at the start of the fight instead of his usual opening barrage? One could make the argument that he can only use it when you Spare him because your guard is down, which doesn't really make sense considering what you've had to endure just to get to that part of the fight, or that Sans is deliberately holding back as an act of mercy, which also doesn't make a whole lot of sense since Sans has no real reason to hold anything back, especially since he knows you can just reset if he kills you.
  • Presumably the same reason that if you get someone's name to turn yellow and attack, it does a ton of damage; you've dropped your guard so it opens you up to an absolutely devastating strike that can't be done otherwise. It might also be that it takes a long time to charge up and would leave Sans vulnerable to actually being hit, so he could only do it if you spare him. Also, he beckons you closer for a hug, so it might be something that can only be done at point blank range.
  • At this point in the No Mercy run Frisk is almost entirely taken over by The Fallen Child, who in turn takes advice from you, the player, and has been implied to be no longer truly human (Sans commenting about you pretending and Asgore mistaking you for a monster, for example). It's entirely possible that the player opting for mercy weakens The Fallen Child and your influence, or breaks their guard so thoroughly to the point that such a devastating attack could even be used against them. If Sans fluffed it and failed to kill, he could possibly be too weak to defend himself against the now very pissed off Fallen Child and player.
  • It's a hug. You can't dodge something he does after deliberately walking over and letting him hold you still. The move taking up your whole window is just illustrating you took a hit at point blank.
  • In the game itself, Sans is the final barrier between you and Asgore. The last defense. But he is aware, to some extent, of you (the player), and knows that you will keep coming back, so just killing your character won't work. The only way for him to defeat you is to, essentially, drive you mad trying to beat him. If there was no hope, you (both the character and the player) would get bored and leave. A chance at success, however small, is what keeps you determined, and what keeps you from ever leaving. And that's what Sans' duty is. To keep you from doing any more damage.

Royal Guard Sans

• Sans's attacks are leagues ahead of Asgore and Undyne, the most powerful warriors in the underground. So why is he not captain of the royal guards or at least among their number?
  • He promised Toriel that he wouldn't harm any humans, so that would be one mark against him for royal guard. Secondly, he's very lazy so it's doubtful he'd even bother trying for that. Also in terms of strength and strategy, Sans is stronger than Undyne and Asgore, but he isn't tougher than them. He only has 1 hp while Undyne takes several hits to beat and while Asgore can be cut down immediately, he at least has a lot more hp.
  • In addition, Sans can't dodge magic attacks with the kind of consistency he can dodge physical ones. The dude has 1 HP; one graze on a bullet board would take him down. Getting into fights with other monsters is something that is very much not in his best interest to do.
  • There's more to being a royal guard than just being strong. Sans doesn't even do his regular job of maintaining puzzles and keeping watch for human activity really. He's even converted one of his guard stands into a hotdog stand so he could slack off from work by doing completely different work. He's to the point where he doesn't even try to stop you as you tear your way through countless civilians, he ONLY directly fights you when you're not just a threat to Monsters, you're a threat to EVERYTHING. Undyne might not be as strong as him, but Monsters only speak about her with lots of respect and reverence. She begins trying to stop you as soon as she hears you're around, and she's so well known and respected that she can channel the hopes and dreams of all monsters in the No Mercy run. Royal Guards are like policemen, they have jobs and reputations. Sans is like a gorilla (no insult intended). He's on a completely different level strength wise than any other person, but he's not going to be chief of police like Undyne could be.
• Because Sans would have refused, or just not did his duties?
• Sans seems to be using his many 'jobs' as a cover for something else. The dialogue in the No Mercy run reveals he and at least one other person ('we') have been watching the timelines. By "slacking off" where presumably pretty much everyone in the Underground can see, nobody ever guesses he is something more than a layabout. It's the perfect cover. Being a guard would make him look too competent.
• All in all, the reason he's not in the Royal Guard is that he's just too freaking lazy to do it, and thus, although he would be the strongest on the guard, he would also be the most useless, as he'd slack off 99% of the time.

Sans's Behavior in a Neutral/No Mercy Run

• Sans knows there's a threat of you killing his brother. In a No Mercy run, he even explicitly states there will be consequences if you do. So why does he not stop you from killing his brother? For that matter, why does he wait until the end of a No Mercy run after you've killed so many people if he's already aware of the danger?
  • Probably because he promised Toriel not to harm you. Even then he only breaks it when he knows there's no choice left but to attempt to stop you/make you reset with his bullet hell, and at the very least he really doesn't want to see you again after killing his brother but staying Neutral otherwise.
  • Two other perspectives. One is he simply hoped you would change before it went too far. Even in his fight when you spare him, he hopes you don't come back/reset the game and bring his brother back. The second would be a gameplay reason. Imagine fighting Sans at the beginning of the game. Even at lvl 19, one level below the cap and dealing only one damage, he's still a tough fight. Taking him on at the beginning of the game would probably be an impossible task.
  • It's possible that Sans cannot hurt the player much when they are at LV 1 (He relies on KARMA to deal the heaviest damage). This is exemplified by the Genocide Route assuming you've played a nicer route first (i.e. skipping entire boss fights, forcing the player into green or blue mode with no tutorials.)
  • Not to mention Sans seems to pretty much expect everything to reset eventually, even if you do damage and kill people you'll just reset back to the beginning sooner or later and bring everyone back. The no mercy run is the only route that can never be fully undone.
    • It's possible Sans has TRIED to change things in previous timelines, but the most likely reality is current Sans wouldn't have that experience and so far as he is aware he has only lived one life — which makes me wonder if the "he doesn't act because he knows it's pointless" theory isn't entirely accurate, but that's another kettle of fishbones. He is aware of the time distortions, he knows they're repeating, but he isn't able to affect them (though fanon often suggests he can to heartbreaking effect, there's no hard evidence of this). He knows they've done this many times, and can hypothesise what you might do based on the evidence they have of those resets, but he doesn't actually remember doing this before and can't be 100% certain what the "best" thing is to do in any situation. Maybe if he acts, or doesn't act, Papyrus will be killed anyway. (Another thing to note is that Sans has 1 HP. He would be ridiculously easy to kill if he would only stand still, and he knows he's no good to anybody dead). I think it's best to think of each Reset worlds Sans as their own individual, entirely separate from their other timeline selves, and they act slightly differently each time.

Sans' Photographs

• In the lab that Sans lets you into if you reload multiple times at the final corridor, checking the leftmost drawer brings up the description "There are photos of Sans with a lot of people you don't recognize. He looks happy". That's still an unsolved mystery for Sans' backstory, and all in all is interesting but not too crucial to the plot. However, when you come back after fighting the True Pacifist Boss Battle, the description changes to "There's a photo album inside the drawer. There are photos of Sans with a lot of people you don't recognize. ... and, one photo of you standing with Sans and all your friends". This is in most likelihood referring to this photo, which you only get after deciding not to stay with Toriel and after finishing the entire credits sequence. This would make sense if somehow Sans managed to keep the photo after a potential reset or load to the last save, but the photo still appears in the drawer even if the player/game has not gone through any sort of reloading after getting the True Pacifist Ending for the first time. Does that mean Sans can access different timelines of different games/playthroughs, even if they're not on the same plane of existence (read: different computers)?
  • Occam's Razor: the photo is taken after you defeat the Final Boss but before you leave the Underground (hence why everyone is together). Sans then placed the photograph into his album and returned to the rest of the group using his pre-established teleportation powers. Just because you first see the photograph after the end credits does not mean the photo was taken after the end credits.

Toriel and Sans (SPOILERS)

• It is mentioned throughout the game that Toriel and Sans were talking to each other through the door leading back to the Ruins and in the pacifist ending, the two of them meet face to face for the first time. What I don't understand is why did Toriel choose to talk to Sans through the door and not step out to see him? Or at the very least, couldn't she invite him to the Ruins to have a friendly face to face conversation?
  • She may have been too timid, or afraid her new 'friend' might report back to Asgore.
  • Pretty much, she's in self-exile so she doesn't want anyone to know who she is because she doesn't want people seeking out the former queen for any reason. Telling jokes through a door is a lot different from trusting someone with her face, especially since Boss Monsters are very distinct and she could be easily connected to Asgore. Note that she doesn't have any hesitation in letting Sans join her in self-exile in a neutral ending where she lives but the Underground goes into Anarchy.

Sans appearing and disappearing

• So is there an explanaiton as to why Sans, after turning the lights off in his battle/skipping your turns, appears then reappears in random location? Is it a reference to how he can appear in multiple places at once without you looking? If yes, then how does he do that and why?
  • In order, a) He has the ability (among others) to teleport; b) Probably the same ability at work; c) Magic, same way he attacks you on a No Mercy run; d) His overall goal is to keep an eye on Frisk (as he promised to Toriel) and see what they're up to—and if there's any signs of Frisk getting onto the No Mercy/Genocide path. If you check Sans' character page, the skeleton bro is a lot more than he appears to be.