History Characters / UndertaleSans

* BadBedroomBadLife: He has a complete mess in his bedroom, including a self-sustaining trash tornado, a jury-rigged light fixture, and an unmade bed. It's only accessible after [[spoiler:the PC reveals their {{Retconjuration}} powers to him, and Sans' laziness and apathy stem from knowing he's trapped in EternalRecurrence]].

* DidYouJustPunchOutCthulhu: Through sheer power of [[CombatPragmatist badassery]], [[TheComputerIsACheatingBastard annoyance]], [[ArsonMurderandJaywalking and persuasion]], Sans is the only character who even remotely stands a chance of [[spoiler:stopping you from destroying the world]].[[note]]Granted, any character could technically hold that title if they happen to be the character who made you give up and Reset, but Sans stands out in that he's the only one fighting against you, the player, rather than your character.[[/note]]

* TheAntiNihilist: The most [[SlidingScaleOfIdealismVersusCynicism optimistic]] way to interpret his character. He's pretty much resigned to his life, or lack thereof, [[spoiler:being determined by someone else's whims]]. He is nonetheless very jovial and friendly to pretty much everyone but those that deserve otherwise, tries to enjoy life to the best of his ability, and even laments [[spoiler:having to kill you if you drive him to it]].

* BadassBoast: He's full of these when he gets serious, but one in particular, which he gives [[spoiler:in the Hall of Judgement]] during a No Mercy run, stands out.
--> '''Sans:''' heh heh heh heh...all right. well, here's a better question. [[DontMakeMeDestroyYou do you wanna have a bad time?]] 'cause if you take another step forward...you are REALLY not going to like what happens next.
** And let's not forget this one, which he gives right before your battle with him:

** Or this one, when you challenge him [[spoiler:after losing his battle three times]]:

* AwakeningTheSleepingGiant: Sans is very, very lazy and generally disinterested in involvement beyond bad puns. [[spoiler:This is largely because the screwy time manipulation that's come about in the Underground has caused him to abandon hope of getting to the surface — but he's still watching how things are playing out. Press his buttons one time too many over the adventure, and he'll decide he "[[LetsGetDangerous can't afford not to care anymore]]".]]

* AlmightyJanitor: He's the Snowdin Forest watchman who is perfectly fine with shirking his duties and moonlighting with several other money-making schemes. He has [[OneHitPointWonder 1 HP]] and his attacks can only do 1 damage. [[spoiler:He also has a ''working knowledge'' of quantum physics and has figured out the timeline is being manipulated ''without'' a fully RippleEffectProofMemory. Oh, and those stats? His attacks ignore MercyInvincibility and apply a DamageOverTime effect, and he can ''dodge'' incoming attacks. IN SLIPPERS.]]

* BadBedroomBadLife: He has a complete mess in his bedroom, including a self-sustaining trash tornado, a jury-rigged light fixture, and an [[ArsonMurderAndJaywalking unmade bed]]. It's only accessible after [[spoiler:the PC reveals their {{Retconjuration}} powers to him, and Sans' laziness and apathy stem from knowing he's trapped in EternalRecurrence]].

* BallisticBone: His main form of attack. [[spoiler:They also inflict KARMA, which drains the player's health over time.]]

* {{Acrofatic}}: Despite the fact that being plump and lazy is [[TheSlacker one of his primary character traits]], Sans is the only character in the entire game who not only has the ability to [[spoiler:avoid your attacks]], but do so [[NonchalantDodge completely effortlessly]]. That said, it's not clear if he has this ability naturally, or if, given his meta awareness, he's simply the only character who [[YouHaveResearchedBreathing thought to do a seemingly-obvious thing]].

* {{Superboss}}: There's ''nothing'' that forces you to fight him; [[EarnYourBadEnding in fact, it's a much-discouraged path]], and he even comments that there's no benefit to it other than 'just because you can, you have to'. But you want your uber-challenging boss fight? ''You got it.''

* BonusBoss: There's ''nothing'' that forces you to fight him; [[EarnYourBadEnding in fact, it's a much-discouraged path]], and he even comments that there's no benefit to it other than 'just because you can, you have to'. But you want your uber-challenging boss fight? ''You got it.''

* BigBrotherInstinct: While unstated in-game, Sans is suggested by WordOfGod to be older than Papyrus, and has an extremely strong instinct to keep him safe and happy. In fact, it's one of his few character traits that remains strongly present no matter what kind of run you're on: in Pacifist and most Neutral runs, he requests of you to play along with his plans to cheer Papyrus up and will express mild offense (a lot coming from him, as he's ''extremely'' even-tempered) if you decline or disagree when he asks if you think he's cool. In high-casualty Neutral runs, he will attempt to shelter Papyrus from the deaths of anybody close to him by telling him they "[[ReleasedToElsewhere went on vacation]]", despite the fact that Papyrus is clearly an adult. Unfortunately, this instinct does very little in terms of actually protecting him from danger, because [[spoiler:he knows full well that not only is he a CosmicPlaything who ultimately can't do anything, but also that he's trapped in a GroundhogDayLoop and Papyrus will be back before long. As a result, while he's clearly [[HeroicSafeMode utterly devastated]] for the rest of the game and will henceforth treat you with nothing but scorn and TranquilFury]], he won't even try to intervene if you decide to kill him.
* BigBrotherWorship: Sans makes it clear on many occasions how cool he genuinely finds Papyrus, for all he messes with him.

** The guy's already [[DespairEventHorizon so jaded at this point]] that you'd think there'd be no way to break him further, but no, there is one surefire way: find the nerve to [[LivingEmotionalCrutch kill his little brother]]. Do that, and Sans will just… [[spoiler:stop being in the game. ''Completely''. Off-screen, he plunges into some kind of HeroicBSOD and/or HeroicSafeMode, never talking to anybody and stalking you in silence, focusing on your general kill count. He'll only show up near the very end in full TranquilFury mode, and if you reach an ending where you can get him to talk to you again afterwards, he makes it very clear that you really, ''really'' hit him in the one place that still hurts]].

** [[spoiler:Sans also manages to invert the trope by being able to "cheat" in quite a few ways during the battle. But seeing as how his goal is to frustrate the player to {{Rage Quit}}ting, it makes quite a bit of sense.]]

* DontMakeMeDestroyYou: Frequently warns you ''not'' [[TemptingFate to keep pushing him]]. You really ''won't'' like what'll happen next if you succeed. He's not bluffing.]]

->''"maybe it's a little strange, but sometimes... it's nice to have someone call you out on being lazy. [[{{Foreshadowing}} even though nothing could be further from the truth]]."''

'''NOTE:''' As a main character, this page has the potential to give away '''major''' spoilers. Proceed with caution if you have not finished the game. ''You wouldn't want to have a bad time, now would you?''

* BewareTheNiceOnes: An extremely chill and amiable guy, Sans is liked by everyone who knows him (except [[TheSociopath Flowey]], obviously) and treats you like an old friend mere seconds after you meet him. It usually takes a ''lot'' of effort to get Sans legitimately angry with you, but if you do… at best, [[spoiler:[[WhatTheHellPlayer he'll call you out for the dirty scumbag you are]]]], and at worst, [[spoiler:''say your prayers and [[ThatOneBoss hope it's over quickly]]'']].

** His combat description when you CHECK him says that he's the "easiest enemy in the game." This is completely untrue, and since [[AlphaStrike he leads with]] [[BeginWithAFinisher his strongest attack]] the moment the fight begins, the player will know — from ''painful'' experience — it's a lie by the time they can read it. Going far enough into the fight will have the game actually confess that reading its messages doesn't seem to be all that useful for you.

* BossCorridor: The [[ExactlyWhatItSaysOnTheTin Last Corridor]] is completely empty until Sans suddenly appears and stops you in your tracks. Subverted in that he does not fight you, but he does assess your actions and deliver judgment, including some well-deserved {{Player Punch}}es if you screwed up. [[spoiler:Double subverted if you go on the No Mercy route, where he decides to actually step into the fray and [[ThatOneBoss gives you one hell of a bad time.]]]]

** [[AlmightyJanitor Sans]] appears to be extremely knowledgeable about almost everything that goes on in the game but [[LazyBum spends all his time loafing around]] and [[PungeonMaster making puns]] for his own amusement. [[spoiler:It is heavily implied that Sans is some form of time traveler/scientist that has observed multiple timelines. The reason he's so lazy is that [[CosmicHorrorStory he knows the truth about how easily the world can be reset regardless of what he does]]. Only on the [[ApocalypseHow Genocide Route]], where the VillainProtagonist becomes a threat [[EvilOnlyHasToWinOnce not just to that timeline but all of them]], does [[NeutralNoLonger Sans actually become motivated enough to fight]], and he's by far [[ThatOneBoss the hardest boss in the game]].]]

* TheCameo: After years of "Sans for [[VideoGame/SuperSmashBros Smash!]]" being a massive MemeticMutation among both communities, it was finally revealed that he would be appearing in ''VideoGame/SuperSmashBrosUltimate'' as a Mii Fighter Costume.

* CombatPragmatist: He pulls just about every dirty trick in the book, and constantly breaks the rules to compensate for his low stats. Some examples include [[BeginWithAFinisher launching a powerful attack right at the start of the battle]], dodging your own attacks, ignoring MercyInvincibility, and hitting you ''during menu selection''. In his second phase, he's also able to change attack patterns on the fly just to screw with you. He also delivers some absolutely ''brutal'' [[BreakingSpeech trash talk]] throughout the fight (and subsequent attempts) to remind you just how much of a scumbag you are, and even pulls an ISurrenderSuckers before delivering a OneHitKill.

* CrouchingMoronHiddenBadass: While he's clearly intelligent, Sans is ''incredibly'' lazy and prone to making immature jokes. [[spoiler:Definitely not the character you'd look to for ThatOneBoss material.]]

* DidYouJustPunchOutCthulhu: Through sheer power of [[CombatPragmatist badassery]], [[TheComputerIsACheatingBastard annoyance]], [[ArsonMurderandJaywalking and]] [[IKnowYoureInThereSomewhereFight persuasion]], Sans is the only character who even remotely stands a chance of [[spoiler:stopping you from destroying the world]].[[note]]Granted, any character could technically hold that title if they happen to be the character who made you give up and Reset, but Sans stands out in that he's the only one fighting against you, the player, rather than your character.[[/note]]

* DontMakeMeDestroyYou: Frequently warns you ''not'' [[TemptingFate to keep pushing him]]. You really ''won't'' like what'll happen next if you succeed. [[ThatOneBoss He's not bluffing.]]

* DrosteImage: He keeps a joke book in his and Papyrus' house which hides a Quantum Physics textbook, which hides another joke book, [[RunningGag which hides another Quantum Physics textbook.]] [[HiddenDepths Pretty good metaphor for Sans himself, actually.]]

** Most infamously, when he uses his "special attack", he says "here goes nothing." What happens next is… [[spoiler:[[ExactlyWhatItSaysOnTheTin literally nothing]]. As in Sans ''refuses'' to end his turn, since he knows that your next move will be his last. So he simply waits, hoping that you'll get so bored that you'll give up and quit. Sadly for Sans, [[InterfaceScrew you give him a taste of his own medicine…]]]]

** Sums up just about ''[[ChewToy most of his life]]''. During his boss battle, we learn that he firmly believes [[spoiler:the world is going to be reset no matter what happens]], despite the fact that [[SourSupporter he still continues to root for the protagonist anyway during the Pacifist Route]] (considering the vastly different circumstances of both routes, however, it's quite possible that he legitimately TookALevelInIdealism during the latter while being pushed further past the DespairEventHorizon in the former). He also makes vague remarks about "never being able to go back", which is most likely related to [[spoiler:the unfixable machine hidden in his basement and to his pictures with people the player character can't recognize.]]

** Pester Flowey enough by completing multiple Neutral Runs, and he will eventually tell you to stay away from 'Smiley Trashbag' for [[spoiler:causing him [[OffscreenMomentOfAwesome 'more than his fair share of resets']]]]. [[spoiler:Then you try to [[KillEmAll walk in Flowey's footsteps]], and ''boy'' [[ThatOneBoss are you in for a surprise.]]]]
* ForgivenessRequiresDeath: If you accept his offer of friendship in No Mercy Run: [[spoiler:"If we're really friends.... you won't come back."]] Because why would he forgive a living person who [[spoiler:has the power to bring everyone back to life (i.e. reset the game) and not use it for that purpose]]?

* GenocideBackfire: His fight at the end of the No Mercy Run can be interpreted as this. He is [[ThatOneBoss the toughest boss of the entire game]] and has brought many players to just give up, but he will actually never fight the player in any other timeline but the one where you literally kill everyone in the Underground.

* GoddamnedBoss: InvokedTrope. [[spoiler:He knows that you can just use SaveScumming to keep trying until you take him down, so he deliberately makes his fight as frustrating as possible to make you RageQuit.]]

** Both are [[PerpetualSmiler smiling]] and [[TheGadfly trolling]] [[StrawNihilist nihilists]] [[GoMadFromTheRevelation who've been broken to discover]] they are characters in a game and that some entity can rewind time in it and undo everything they did. [[spoiler:However, while Flowey actually lived as a video game player, rewinded time to see everything himself, [[TheFourthWallWillNotProtectYou actually remembers everything you did in detail and won't hold himself to taunt you with it]], Sans' knowledge on the question is a mystery, but he became fatalist because of it and can only interpret your resets through secret codes and by looking at the Human Child's facial expressions.]]
** Also, both of them are [[ThePrankster pranksters]], [[VoiceChangeling have a talent]] [[ManOfAThousandVoices for imitations]], and [[MysteriousWatcher watch for the protagonist in the shadows]]. [[spoiler:Flowey avoids contact, plays cruel pranks on you consisting of giving you a HopeSpot, makes imitations in the same vein (for example, the infamous Echo Flower in Waterfall where he mimics Toriel's voice before taunting you), and takes action [[NiceJobBreakingItHero once you've fought Asgore yourself]] to take the Human Souls for his own benefit. On the other hand, Sans frequently chats with them, [[ThePrankster plays childish]] [[EyepiecePrank pranks on them]][[note]]for example, the telescope prank in Waterfall (though it could be more serious than it seems to be)[[/note]], offers them a dinner where he shows his talent by imitating Toriel, judges them before they meet the King, and [[ThisIsGonnaSuck only takes action if they go too far]].]]

* GroundhogPeggySue: Sans is an odd case; he's aware of [[spoiler:being stuck in a time loop and is very alert to when a reset happens]], but he carries over little to no memories of previous timelines to the present day. During a Pacifist run, all he does is play the role of a funny PungeonMaster so you could have a satisfying experience with the game [[spoiler:and stop the resets for good once you reach the GoldenEnding]]. ''[[ThatOneBoss If you decide for a Genocide run, however...]]''

* IFellForHours: Weaponized for his [[ThatOneAttack penultimate attack]], combined with GravityScrew and SpikesOfDoom. And it's not even the deadliest part of said attack. At first, the attack looks admittedly quite funny, with Sans pulling various poses as the player’s soul flies past… until it takes a decisive swerve when the last sprite of Sans seen in this segment of the attack features him with dark eye sockets.

* LethalJokeCharacter: Sans is described as the easiest enemy who can do only a single point of damage per hit. As it turns out, what this really means is [[spoiler:1 ATK ''per frame'']]. And boy, does he take advantage of this to the extreme. Not only does he attack at ridiculous rates and in ridiculous amounts, but also, [[spoiler:the 1 ATK means his attacks pierce MercyInvincibility to deal constant damage and leaving a poison effect.]] And they're some of the most ''intense'' in the entire game, because of the speed and range of his attacks (in some cases, there's literally just one tiny spot in the box where you can hide). [[spoiler:He leaves his 1 defense point moot by constantly dodging your one hit kill swings.]]

* PreAssKickingOneliner: [[spoiler:"it's a beautiful day outside. birds are singing, flowers are blooming... on days like these, kids [[KidsAreCruel like you]]... '''[[ThisIsUnforgivable Should be burning in hell.]]'''"]] This is even played with to mess with you even further — he'll cut the speech off mid-sentence and immediately jump into his opening routine entirely at random.

** While Flowey has been pushed to being one, Sans has a lot of icon power on the internet, to the point where people who have only glanced at ''Undertale'' but never played it can probably recognize what game he's from when they see him elsewhere. Tends to happen when you're one of the most liked characters [[spoiler:and a freakishly difficult and memorable BonusBoss, which is verging on ItWasHisSled in most circles]].

* TheStoic: Downplayed in that his casual, comically-smug attitude doesn't change very much no matter what mood he's trying to get across. His emotional range in general is very subdued, even on the rare occasions where he's [[TranquilFury clearly]] [[DissonantSerenity feeling]] [[HeroicBSOD otherwise]].

* WalkingSpoiler: There's quite a bit more to Sans than just the joke-loving skeleton you meet early on. Those avoiding spoilers take heed: even glancing at fanart of Sans will almost certainly give away something about his character. And, y'know, there are a lot of spoiler marks here for a reason. [[spoiler:To sum up, Sans is one of the two {{Fourth Wall Observer}}s, '''the''' FinalBoss of the [[KillEmAll Genocide Route]] plus [[WakeUpCallBoss how]] [[ISurrenderSuckers he]] [[OffscreenTeleportation fights]], and the fact [[IWarnedYou he warns you if you win]] that it's the PointOfNoReturn.]]

* AllPowerfulBystander: [[DownplayedTrope Downplayed.]] [[spoiler:He seems to be more powerful than everyone else in the underground]], and stays away from fighting because of his laziness [[spoiler:and how he knows that the world will just get reset anyway no matter what]], though he's also fully aware that [[spoiler:unlike everyone else, you are still so much more powerful than him due to your determination that fighting you is a HopelessBossFight. This is deconstructed however, as due to the fact he does not make the decision to fight except in the worst possible timeline, he allows the player to get away with murdering monsters (including his own brother) despite the fact that if he took a stand earlier on, he'd probably be far more successful. This is due to him being aware of the Reset feature and realising that no matter what the player does, it will always be reversed at some point, 'except' in the No Mercy Run where the destruction of the universe permanently alters the game's files.]]

* AlphaStrike: Sans does not mess around on the [[KillEmAll Genocide Route]]. His first attack is his most powerful, a brutal gauntlet of [[spoiler: GravityScrew, SpikesOfDoom, and BeamSpam using [[WaveMotionGun Wave Motion Guns]] that can and most likely will waste you within seconds. To top it all off, [[NoFairCheating he's also the only enemy in the game that gets the first turn]].]]
* AmbiguouslyHuman: Ambiguously ''monster'', in this case. You're normally given no reason to question him, considering he lives among [[FantasyKitchenSink far more bizarre creatures]] that are still clearly monsters, but what we learn about him [[spoiler:at the end of a genocide route]] is another matter entirely. [[spoiler:Not only does he have an awareness of the very mechanics his game is built upon, but he has the ability to ''override'' most of them as well, something no other character in the game is shown to be able to do except [[EldritchAbomination Photoshop Flowey]], who has ''six human souls'' to his name. This allows him to be ''tremendously'' dangerous in combat despite his bare-minimum stats.]] During the battle, he tells you "look. i gave up trying to go back a long time ago. and getting to the surface doesn't really appeal anymore, either.", suggesting he's somehow either in the wrong place, [[FishOutOfTemporalWater in the wrong time]], or both. And even though there's some dispute over the ''precise'' substance, [[spoiler:something red that definitely ''looks'' like blood (it might be ketchup) spills out when he's cut open, despite the fact that monsters are MadeOfMagic and don't shed blood]]. On top of all this, he's the only character in the game who [[spoiler:[[SoundOnlyDeath does not turn to dust on-screen]]]], which some have taken as [[TheLawOfConservationOfDetail a suspiciously specific detail to exclude]].
* AmbiguousDisorder: While his laziness and apathy to almost everything around him (that isn't Papyrus) is played for laughs more often than not, a lot of what he does and says rings eerily close to someone suffering from depression. [[spoiler: In the final Pacifist-route fight, his lines notably aren't hostile as with the rest of your brainwashed friends, but just straight-up hopeless and sorrowful, such as his line in which he advises you to "just give up. i did." In his boss fight in the genocide route, he even discusses this, briefly musing if his refusal to do anything stems from the knowledge that it won't matter anyway or if he's just actively looking for an excuse to be lazy.]]
* AmbiguousSituation: Look at that pixel pattern in the center of his chest. Is that his hoodie's zipper and a white undershirt, or is that his bare ribs and sternum? (His ''Smash Bros'' appearance suggests it's the former).

** Sans himself is in a very abstract, psychological example of this trope due to his [[spoiler:awareness of you and Flowey's timeline manipulation. Since the two of you have the ability to start the game over again whenever you please, he sees his life as an endless GroundHogDayLoop that only you can set him free from, and in almost all circumstances his faith in you isn't exactly solid. Not even death would release him, as you have the ability to reverse that without a hitch, and as such he's left borderline-crippled with nihilistic depression.]]

** Sans' DamageOverTime effect can only bring your HP to 1 and cannot actually kill you. Similarly, his InterfaceScrew attacks do not have DamageOverTime effect and can only bring your HP down to 1.

* TheAntiNihilist: The most [[SlidingScaleOfIdealismVersusCynicism optimistic]] way to interpret his character. He's pretty much resigned to his life, or lack thereof, [[spoiler:being determined by someone else's whims]]. He is nonetheless very jovial and friendly to pretty much everyone but those that deserve otherwise, tries to enjoy life to the best of his ability, and even laments [[spoiler:having to kill you if you drive him to it.]]
-->'''Sans''': [[spoiler:sounds strange, but before all this i was secretly hoping we could be friends.]]

* BadBedroomBadLife: He has a complete mess in his bedroom, including a self-sustaining trash tornado, a jury-rigged light fixture, and an [[ArsonMurderAndJaywalking unmade bed]]. It's only accessible after [[spoiler:the PC reveals their {{Retconjuration}} powers to him, and Sans' laziness and apathy stem from knowing he's trapped in EternalRecurrence.]]
* BadassBoast: He's full of these when he gets serious, but one in particular, which he gives [[spoiler: in the Hall of Judgement]] during a No Mercy run, stands out.
--> '''Sans''': heh heh heh heh...all right. well, here's a better question. do you wanna have a bad time? 'cause if you take another step forward...you are REALLY not going to like what happens next.

--->'''Sans''': it's a beautiful day outside. birds are singing, flowers are blooming. on days like these, kids like you... [[spoiler:'''[[LetsGetDangerous Should be burning in hell]]'''.]]
** Or this one, when you challenge him [[spoiler: after losing his battle three times]]:
--->'''Sans''': hmm. that expression...that's the expression of someone [[spoiler:who's died thrice in a row]]. ''[{{beat}}]'' hey, what comes after "thrice," anyway? [[PrepareToDie wanna help me find out?]]

* BadassOnPaper: Inverted, checking his stats says that he has the worst stats in the game. While this ''is'' technically true, his ATK stat of 1 [[spoiler:ignores MercyInvincibility, his attacks are quite large and thus hard to avoid]], and his HP of 1 is irrelevant — [[spoiler:he dodges every single attack while fighting you.]]

* BeginWithAFinisher: When you fight him in No Mercy, he opens with his strongest attack right away: [[spoiler:a combination of GravityScrew, SpikesOfDoom, and BeamSpam with WaveMotionGun.]] Sans lampshades his usage of the trope:

* BeneathTheMask: Overlapping with SadClown, it's no surprise that Sans has a lot going on under his smiling skull. Even though he comes off as someone who truly enjoys pranking and making [[PungeonMaster bad puns]], Sans doesn't always speak in the goofy Comic Sans font and [[spoiler:he hides the worst secrets of the game. His laziness can be attributed to his heavy depression due to the EternalRecurrence he is trapped in and the friends he lost a long time ago. He no longer cares about the world and has grown huge apathy towards his environment, with the only exceptions being [[LivingEmotionalCrutch Papyrus]] and the promise he made to Toriel.]] He usually sneaks in his real thoughts as "jokes"; sometimes even the player wouldn't notice the hidden implications.
* BewareTheNiceOnes: An extremely chill and amiable guy, Sans is liked by everyone who knows him (except [[TheSociopath Flowey]], obviously) and treats you like an old friend mere seconds after you meet him. It usually takes a ''lot'' of effort to get Sans legitimately angry with you, but if you do... at best, [[spoiler:[[WhatTheHellPlayer he'll call you out for the dirty scumbag you are]]]], and at worst, [[spoiler:''say your prayers and [[ThatOneBoss hope it's over quickly]]''.]]
--> '''Sans''': it's a beautiful day outside. birds are singing, flowers are blooming... on days like these, kids like you... [[spoiler:[[PreAsskickingOneLiner Should be burning in hell.]]]]

* BlankWhiteEyes: [[InvertedTrope Inverted]] with Sans, [[BlackEyesOfEvil whose eyes go all black when he’s serious]].

** His combat description when you CHECK him says that he's the "easiest enemy in the game." This is completely untrue, and since he leads with his strongest attack the moment the fight begins, the player will know — from ''painful'' experience — it's a lie by the time they can read it. Going far enough into the fight will have the game actually confess that reading its messages doesn't seem to be all that useful for you.

* ABloodyMess: Sans, the [[spoiler:FinalBoss of the Genocide Route, bleeds when you kill him]], despite the fact that it’s been established that monsters are made of magic and don’t bleed. It is often theorized by fans that this is actually ketchup, because he can be seen chugging a bottle of ketchup at Grillby’s if you decline from using it yourself. Others theorize that [[AmbiguouslyHuman he’s not even a monster]], in which case the trope is {{Subverted|Trope}}.

* BossRemix: "Song That Might Play When You Fight Sans" is an uptempo version of "sans." with a bit of "Bonetrousle" at the end.[[spoiler:Subverted in that it doesn't play at all in the game. Instead, "MEGALOVANIA" plays.]]

** The guy's already [[DespairEventHorizon so jaded at this point]] that you'd think there'd be no way to break him further, but no, there is one surefire way: find the nerve to [[LivingEmotionalCrutch kill his little brother]]. Do that, and Sans will just... [[spoiler:stop being in the game. ''Completely''. Off-screen, he plunges into some kind of HeroicBSOD and/or HeroicSafeMode, never talking to anybody and stalking you in silence, focusing on your general kill count. He'll only show up near the very end in full TranquilFury mode, and if you reach an ending where you can get him to talk to you again afterwards, he makes it very clear that you really, ''really'' hit him in the one place that still hurts.]]

** [[AlmightyJanitor Sans]] appears to be extremely knowledgeable about almost everything that goes on in the game but [[LazyBum spends all his time loafing around]] and [[PungeonMaster making puns]] for his own amusement. [[spoiler: It is heavily implied that Sans is some form of time traveler/scientist that has observed multiple timelines. The reason he's so lazy is that [[CosmicHorrorStory he knows the truth about how easily the world can be reset regardless of what he does]]. Only on the [[ApocalypseHow Genocide Route]], where the VillainProtagonist becomes a threat [[EvilOnlyHasToWinOnce not just to that timeline but all of them]], does [[NeutralNoLonger Sans actually become motivated enough to fight]], and he's by far [[ThatOneBoss the hardest boss in the game]].]]
** Depending on the ending, Sans can get a job where he's surprisingly competent. If Mettaton becomes king, [[spoiler:Sans becomes his personal agent]]. If Papyrus is crowned king, [[spoiler:Sans does all the administrative work to spare him from broken by politics.]]
* BrokenAce: In theory, Sans should have it made: he's nice, he's quick with a joke, he's got his own kind of laid-back charisma, and he makes friends so easily he's able to get chummy with [[spoiler:the queen of all monsters]] without even trying or telling her her name (or vice-versa). He's got a great house, an easy job, a loving brother, and a town full of people who all know his name, with one character having some slight ShipTease with him (that being the drunk rabbit NPC at Grillby's). He's also [[spoiler:one of the most powerful monsters in the underground without [[InexplicablyAwesome any time wasted on explaining why]], is extremely smart with a deep scientific background, and has a lot of useful odd powers like teleportation.]] His one and only apparent flaw, really, is his extreme laziness, and even then, it's used mostly for harmless jokes and only serves to make him more lovable than anything. But, as you've probably guessed from the abundance of spoiler tags on here, [[HiddenDepths Sans is a far deeper character than he seems]]. Beneath everything, [[spoiler:Sans is a deeply cynical nihilist struggling with self-loathing, existential exhaustion, and, according to many fans, crippling clinical depression. His backstory is extremely vague, but it's clearly still affecting him deeply, as it involved the death/disappearance of many people Sans was close to, including a character fairly heavily implied to have a familial tie with him. In addition, he alone knows that the world he lives in is trapped in a GroundhogDayLoop and, as such, finds it almost impossible to care about anyone or anything other than [[LivingEmotionalCrutch his brother]]. There's also evidence that he may be a drinker to some degree, and if you read deeper into the game's writing, you'll find that the vast majority of his relationships don't go further than friendly acquaintanceship.]] Sans may have the building blocks to be the underground's number-one big shot, but without the care or means to arrange them properly, all he's really amounting to is a lazy bum who's just barely able to make ends meet. Were it not for his brother, he'd likely not even have the motivation to properly take care of his basic necessities.

* CombatPragmatist: He pulls just about every dirty trick in the book, and constantly breaks the rules to compensate for his low stats. Some examples include launching a powerful attack right at the start of the battle, dodging your own attacks, ignoring MercyInvincibility, and hitting you ''during menu selection''. In his second phase, he's also able to change attack patterns on the fly just to screw with you. He also delivers some absolutely ''brutal'' [[BreakingSpeech trash talk]] throughout the fight (and subsequent attempts) to remind you just how much of a scumbag you are, and even pulls an ISurrenderSuckers before delivering a OneHitKill.

* TheComputerIsACheatingBastard: One way to look at Sans' battle is him being the ''only'' aversion to the trope. He can do literally ''anything'' you can during your battle. [[spoiler:Both of you can dodge, both of you don't give mercy invincibility to your targets, both of you can feign offering mercy to instant kill a tough foe, and both of you can attack the other when it isn't your turn. You just happen to do the last one better in order to finally win.]]

** There is nothing he can do to stop [[spoiler:the constantly repeating time loop he's trapped in]], so he eventually just numbed himself to all of it. Unless the player carries out a Genocide run, he usually just shrugs off any deaths that happen and mocks you in the end for causing them, [[spoiler:knowing that it'll be reset anyway]]. The one and only thing you can do that really manages to get to him is [[LivingEmotionalCrutch murder his beloved brother]], which sends him into a full-on HeroicSafeMode at worst. And if you do go full Genocide, well... [[spoiler:he may ''pretend'' to take it in stride when he dies, knowing the entire world is about to be destroyed, but [[BrokenSmile the look in his eyes gives him away]]]].

* TheConscience: Sans is literally ''your'' moral compass. He's a reflection on everything you do during your journey through the Underground. He'll [[YouBastard chastise you if you kill]] randomly/indiscriminately, or he'll be your best friend ever if you're benign. Kill everyone, and watch out, [[BewareTheSillyOnes he'll come down upon your wickedness like a ton of bricks]]. Even during the final fight, he's not fighting for the Underground's sake... ''you've already destroyed everything he knew and loved''. [[spoiler: He's fighting for YOUR sake as well, knowing full well that if you successfully get past him, you're eternally damned, as the Fallen Child will claim your soul.]]

* CrouchingMoronHiddenBadass: While he's clearly intelligent, Sans is ''incredibly'' lazy and prone to making immature jokes. [[spoiler:Definitely not the character you'd look to for ThatOneBoss material]].

* DamageOverTime: In addition to [[spoiler:massive direct damage]] when you touch them, his attacks also leave a [[spoiler:slow damage over time effect called Karmic Retribution.]] The more you get hit, the longer this effect lasts.

** Sans spends the entire fight playing on your expectations and trying to catch you off-guard. How do you defeat him? [[spoiler:By catching ''him'' off-guard with a surprise attack]] while he taunts you after pulling yet another NonchalantDodge. Especially notable is that [[spoiler:you're not ''supposed'' to be able to attack twice in one turn. He bends and breaks combat rules, then gets done in by the same approach.]]
** He can inflict this on you. Earlier, Papyrus spared you and offered a hug, only to be killed while his guard was down. Midway through the fight with Sans, he tries to spare you. [[spoiler:If you accept his mercy, he also offers a hug, then kills you while you're off-guard]].

** Another happens at the end of No Mercy, where he turns the conventions of Turn-Based [=RPGs=] on their head. [[spoiler:He ''starts'' the fight with his strongest attack, powerful enough to waste you within moments. He plays into the expectation that every boss battle has that BattleIntro — only to ''[[TalkToTheFist skip]]'' said intro to sucker-punch you. You may have 99 ATK, but there's no Dodge stat in this game, meaning there's nothing that says he can't just sidestep your attacks. And he knows that Scratch Damage will ''hurt'', even against 99 DEF, [[DeathOfAThousandCuts when done a lot, with added poison effect.]] Then he starts to outright cheat by not letting you have your turn in peace, attacking you while it's your turn. And this is all before his space/time bending abilities, tricking you into {{Smash Cut}}s after Smash Cuts.]] Needless to say, this makes for a ''very'' difficult battle.

* DespairEventHorizon: He's goofy and a PungeonMaster, but underneath that big grin, Sans... Sans is not well. [[spoiler:Living with the knowledge that at any second, your life can be irrevocably snatched away from you, for every minute of the day tends to do that to a guy.]]

** When he decides to step in and take action [[spoiler:at the end of Genocide run, he’s pretty much resigned to [[HopelessBossFight his tragic fate]]. But knowing you’re about to destroy the world...]] he just can’t afford to not care anymore. He gives one hell of a final fight with the hopes of getting you to RageQuit or reset to a more merciful game route, but at the end of the day, you have the SaveScumming ability that he has no counter against.

* DidntSeeThatComing: Sans is savvy enough to keep his guard up at all times, even when he's offering reconciliation or ''sleeping''... [[spoiler:But he didn't expect you to be able to attack two times in a single turn.]] [[WideEyesAndShrunkenIrises The look on his face]] says it all.

* DoubleMeaning: His pre-battle speech, specifically the bit where he said how you are "REALLY not gonna like what happens next", can easily be interpreted as how difficult the fight is going to be. However, reading his lines further, specifically "Seeing what comes next" and "Don't say I didn't warn you..." when you mortally wound him, also opens the interpretation that [[spoiler:'what happens next' is an ApocalypseHow caused by the Fallen Child followed by a HeelFaceDoorSlam where you must give up your soul to restore the world if you wish to return.]]
* TheDreaded: Anybody who successfully invokes Sans's wrath learns to fear him. Flowey states in a post-Neutral conversation that [[spoiler:Sans is the only thing that has kept him from reaching Asgore on his No Mercy runs, and he's had to reset multiple times to avoid him; the only time Flowey gets the better of him is in the True Pacifist run by catching him and everyone else off-guard. The Fallen Child, despite expressing nothing but contempt and confidence during the rest of Genocide Run, will [[OOCIsSeriousBusiness express concern]] only when they have to fight Sans.]]

** Downplayed when he suggests [[spoiler:that the player is responsible for all the resetting of the timelines that he's noticed. It's true that the player is responsible for all the resetting ''after'' Frisk falls into the realm of the monsters. But there was plenty of resetting ''before'' that point, too. Flowey is known to have done plenty of resetting before you and Frisk showed up, and a piece of dialogue with Toriel on a second (non-True Reset) playthrough of the game suggests that the human children from before also had this capability.)]]

** If you CHECK him in battle, he is described as "Can only deal 1 damage." This is true, but [[spoiler:he dodges all your attacks, and his rapid-fire attacks override MercyInvincibility and leave behind residual damage, meaning every frame that heart touches his bone attacks will drop your HP point-by-point very rapidly.]]
** Most infamously, when he uses his "special attack", he says "here goes nothing." What happens next is... [[spoiler:[[ExactlyWhatItSaysOnTheTin literally nothing]]. As in Sans ''refuses'' to end his turn, since he knows that your next move will be his last. So he simply waits, hoping that you'll get so bored that you'll give up and quit. Sadly for Sans, [[InterfaceScrew you give him a taste of his own medicine...]]]]

** "Song That Might Play When You Fight Sans" is a BossRemix of "sans." [[spoiler:The operative word is "might"; the song isn't even in the game's files and Sans' boss music is "MEGALOVANIA"]].

** He is really, ''really'' lazy, even if the cause of that is up for debate. While it's played for laughs every time it comes up for the most part, [[spoiler:he winds up exhausted should the player make it all the way to the end of his final barrage in No Mercy. From there, he starts to doze off...]]
** When Sans unleashes his special attack, which turns out to be [[spoiler:prolonging his turn to get you to quit]], the only way to beat him is to [[spoiler:drag the box you're in over to the 'FIGHT' option. The only hint you're given to do this? Any time you get too close to the lower left-hand corner, Sans' eye flashes blue, and you are thrown back to the center. His precaution is ultimately what causes his death.]]

* FinalBoss: Of the [[spoiler:No Mercy]] route. After him, [[PostFinalBoss you move on to Asgore]], [[spoiler:[[ZeroEffortBoss who's automatically one-shotted]], so he's the last true boss you'll fight.]]

** He's also one to [[spoiler:Flowey]]. Both are {{Fourth Wall Observer}}s who present themselves as being harmless and goofy, but hide a much more cynical personality beneath that veneer. But while Sans is a loyal friend and loving brother who only acts against you if you go out of your way to be as evil and monsterous as possible, [[spoiler:Flowey]] is using you the entire game and attempts to murder you in cold blood several times no matter how kindly you treat him.

** When you first enter Snowdin, there's a large branch in the path that's "too heavy to move", implying that it's fairly large. Once Sans starts following you through the forest, you hear a loud cracking sound. If you backtrack a bit, you'll notice that the branch has been ''snapped in half''. [[spoiler:Considering Sans and the Human Child are about the same size and a skeleton is probably much lighter than a human, Sans must have crushed it with magic... and demonstates this ability to you first-hand during his fight, where he flings your soul violently against the walls, ceiling, and floor.]]
** During the epilogue of the GoldenEnding, Papyrus got his wish of driving a car on the highway. Which then got outsped by Sans on a tricycle. Was Papyrus just driving ''really'' slowly? (But then again, he's on the highway.) [[spoiler:...Or does Sans have hidden talents?]]
** Pester Flowey enough by completing multiple Neutral Runs, and he will eventually tell you to stay away from 'Smiley Trashbag' for [[spoiler:causing him [[OffscreenMomentOfAwesome 'more than his fair share of resets']]. Then you try to [[KillEmAll walk in Flowey's footsteps]], and ''boy'' [[ThatOneBoss are you in for a surprise.]]]]

* FragileSpeedster: Sans is [[spoiler: a OneHitPointWonder]], but is skilled at dodging and makes very rapid attacks with his magic. Good luck getting even one hit in.
* FriendlyEnemy: This is how he [[BeneathTheMask truly]] perceives [[spoiler:the protagonist throughout most of the game. He deliberately acts friendly to try and keep them happy on a Pacifist playthrough, and while it's likely sincere to some degree, he still clearly remains wary of their actions. Deep down, he wishes to have a genuine friendship with them, however; he admits as much during his boss battle.]] By the end of the Pacifist route, while he does unambiguously care about them, it's still somewhat up to debate how much he truly trusts them due to his paranoia.

* FrothyMugsOfWater: Or rather, a nice bottle of ketchup. Sans slammed the bottle like water. Fans even like to imagine him getting [[DrunkOnMalts drunk off it.]]
* FrozenFace: Downplayed in that he's able to emote with his eyes, but doesn't seem capable of changing the shape of his mouth, giving him a permanent skeletal grin. [[spoiler:[[SubvertedTrope Or so we're led to believe]]. Look very closely during two specific moments (when Flowey grabs him near the end of the Pacifist route and when he gets fatally wounded near the end of the Genocide route), and you'll see the corners of his mouth shift very slightly, turning his grin into an expression of shock and pain. It's still up to interpretation, however, if this is the full extent of his ability to do so, or he's actually capable of emoting normally and simply [[StepfordSmiler chooses not to]]. It's debatable whether or not this can be considered canon, but in the Undertale Kickstarter Reward Tier video, there's a brief moment where Sans takes out a drink and drinks it, and when he does, his [[FreezeFrameBonus mouth actually closes.]]]]

** During the PlayableEpilogue, if you [[spoiler:call Toriel (who answers you through text), she lends the phone to Sans because it's too small for her hands: he uses it to mock her [[MyBelovedSmother motherly demeanor]]. She then takes the phone back to mock his BigBrotherInstinct.]]
* GameFace: Sans is always grinning, constantly looking around to make aside glances while he talks, giving him a cheerful, animated feel. [[spoiler:When his eyes disappear and he just ''stares'' straight at you with empty, pitch-black eye sockets, you know things have just gotten real. And when his left eye starts [[GlowingEyesOfDoom glowing]]... start praying, for all the good it will do.]] On the flip side, [[spoiler:his eyelights also disappear at one point in a Pacifist run, when he tells you his secret secret codeword: "I'm the legendary fartmaster.", implying confiding such is SeriousBusiness.]]

* GlassCannon: He's capable of rapidly shredding down your considerable HP, yet he himself only has [[spoiler:1 HP]]. To make up for this, he [[spoiler:dodges each and every one of your attacks until the very end.]]

* GodzillaThreshold: ''You''. The one thing that can make Sans get off his ass and actually try is the threat of [[spoiler:a player character about to KillEmAll and poison every timeline in the game.]]

** Also, both of them are [[ThePrankster pranksters]], [[VoiceChangeling have a talent]] [[ManOfAThousandVoices for imitations]] and [[MysteriousWatcher watch for the protagonist in the shadows]]. [[spoiler:Flowey avoids contact, plays you cruel pranks consisting of giving you a HopeSpot, makes imitations in the same vein (for example, the infamous Echo Flower in Waterfall where he mimics Toriel's voice before taunting you) and gets into actions [[NiceJobBreakingItHero once you've fought Asgore yourself]] to take the Human Souls for his own benefit. On the other hand, Sans frequently chats with them, [[ThePrankster plays childish]] [[EyepiecePrank pranks on them]][[note]]for example, the telescope prank in Waterfall (though it could be more serious than it seems to be)[[/note]], offers them a dinner where he shows his talent by imitating Toriel, judges them before they meet the King and [[ThisIsGonnaSuck gets into action if they go too far]].]]

* GoodIsNotSoft: Although Sans is a genuinely nice guy and almost always acts it, [[spoiler:he was apparently completely prepared to murder you the moment you stepped out of the Ruins if not for a promise. While his implied motivation for doing so -- ridding the world of the creature that he believes is the cause of the time anomaly his world is stuck in -- was clearly good (and, in many runs, completely justified), it still speaks volumes that he was willing to stone-cold murder a child in order to achieve it.]] And, if you kill enough people to make him [[spoiler:intervene and fight you,]] he treats you absolutely ''ruthlessly''; with the exact same smug-as-hell attitude he always has, [[spoiler:he insults you, mocks you, torments you with deliberately-unfair attacks, cheats, lies, rubs his own power in your face -- whatever it takes to discourage you enough that you stop playing, since he knows that's the only way he can possibly save everybody at this point]].

** Sans compares you starting and restarting the timeline via saves as this [[spoiler:in the Genocide path as you're fighting him. Part of his laziness is because he knows how futile everything would be if it all resets again.]]

* HeroOfAnotherStory: It's plain as day once you've learned what he knows that before [[spoiler: Frisk]] came around, Sans was the only one working behind the scenes trying [[spoiler: to save the Underground from Flowey]]. He's been keeping tabs on [[spoiler:the activity of the timeline, has been working diligently on some kind of machine in the basement of his home, and he keeps tabs on virtually the entire Underground with a little help from his teleporting shortcuts.]] To top it off, when you face him in battle, [[spoiler:he can attack you at all times and avoid all attacks, almost as if ''he'' was the player character and ''you'' were the boss monster.]] If you complete a few neutral runs in a row, [[spoiler:Flowey]] warns you to steer clear of Sans, as he had barred [[spoiler:Flowey]]'s path multiple times before, and caused him to reset. [[OffscreenMomentOfAwesome Successfully.]]
* HeroicSafeMode: One could say this is his default mode during [[spoiler:all runs]]. In Neutral and Pacifist, he [[BeneathTheMask acts friendly]] towards the player to keep his world (especially [[LivingEmotionalCrutch his brother]]) safe and stalks them around to keep tabs on their kill count. [[spoiler:If you kill his brother or start a Genocide run, this mode is taken UpToEleven; he stops trying to befriend you and only focuses on trailing your actions, until the Judgement Hall where he either gives his judgement with very clear {{Tranquil Fury}} or outright fights you to save the world.]]

* HoistByHisOwnPetard: After an entire fight of throwing InterfaceScrew after InterfaceScrew at you, you beat his 'special attack' -- [[spoiler:i.e. him refusing to make his next move so you can never take your turn]] -- by breaking the interface yourself, allowing you to [[spoiler:press the Attack button in spite of it not being your turn. When even that doesn't work, The Fallen Child says "fuck it" and hijacks control from you to finish the job.]]

* HopelessBossFight: His battle in the No Mercy run is this. [[spoiler:Not for you, but for ''him''.]] While he can (and will) kill you very quickly and messily, [[spoiler:he knows it won't do any good since you can just reload your save and try again, and it's only a matter of time before you finally defeat him. The best he can hope for is to try to get you to RageQuit from the difficulty.]]

** If you [[spoiler:kill him]] and then reset the battle twice, he will provide a unique piece of dialogue at the opening of each new fight which suggests that he might be feeling a bit fearful himself. Of course, that's just one way of interpreting it -- given his lack of voice acting and [[TheStoic very unreadable demeanor]], they could just as easily mean he's [[WorthyOpponent impressed]], surprised, or just outright disgusted.

* IFellForHours: Weaponized for his [[ThatOneAttack penultimate attack]], combined with GravityScrew and SpikesOfDoom. And it's not even the deadliest part of said attack. At first, the attack looks admittedly quite funny, with Sans pulling various poses as the player’s soul flies past... until it takes a decisive swerve when the last sprite of Sans seen in this segment of the attack features him with dark eye sockets.
* IGaveMyWord: Sans hates making promises, but if you can get him to make one, you bet your life he'll keep it. Deconstructed however, as you can ruthlessly slaughter just about anybody you want in the underground, up to and including his own brother, and despite the pain it clearly causes him, [[spoiler:he ''still'' won't break the promise he made to Toriel to keep you safe. Only once you're at the end of a Genocide route and he knows for sure that you're going to destroy ''[[OmnicidalManiac everybody]]'' [[OmnicidalManiac and]] ''[[OmnicidalManiac everything]]'' if he lets you live does he finally set this commitment aside to try and stop you, and even then, the last thing he does before attacking you is apologize to her for it]]. This decision is somewhat justified, however, since [[spoiler:he's aware of your ability to reset the game, so he knows that you're more than likely going to start over shortly after you finish and everything will be back to normal. It's only on a full Genocide route that everything gets destroyed ''permanently'' with every future time-reset variation irrevocably tainted, hence him breaking the promise.]]
* IKnowYoureInThereSomewhereFight: Sans' comments at the midway point of his boss fight has him call out to "someone who wanted to do the right thing", followed by a plea for them to let it end and reset. It's not made clear if [[spoiler:he can remember a previous Pacifist run, can sense Frisk's kind heart beneath the OmnicidalManiac the Fallen[=/=]the Player has become, or if he's simply bluffing, but it's clear he knows this ''isn't'' how it's supposed to be, and he's trying to get Frisk to realize that too. Unfortunately, Frisk is either [[LossOfIdentity completely gone]] or [[AndIMustScream still can't break free from your control]], so the effectiveness of this plea comes down to it reaching the player, not Frisk.]]

* ItsPersonalWithTheDragon: [[spoiler:Any player who plays a No Mercy run only to fight Sans apply this trope on him by default]].
* ISurrenderSuckers: Do you enjoy sparing people only to kill them when their guard is down? Well, if you think [[spoiler:Sans is being sincere when he offers a truce to a mass murderer like you... [[KarmicDeath prepare to get dunked on.]] Why would he let you go so easily if [[ApocalypseHow you're going to end everything]]?]]
* ItNeverGetsAnyEasier: It's strongly implied that the reason Sans acts so [[DissonantSerenity bizarrely nonchalant]] on most Neutral runs, chatting it up and being friendly with you despite the fact that you could be killing people left and right, is because [[spoiler:he knows he exists within a GroundhogDayLoop. Once you're done, you're almost certainly going to reset the game and send everything back to the way it was before, so he doesn't waste time mourning or fearing for his people's future.]] However, there is still one thing you can do in a Neutral run that will never fail to [[HeroicBSOD cut him to the core]], no matter how many times you do it: [[LivingEmotionalCrutch kill his brother]].

** Shortly before fighting Papyrus in the Genocide run, Sans will take you aside and give you a very clear warning: if you continue down the path you're on, you're gonna have a bad time. Should you ignore his warning and continue killing, it will be the last thing Sans tells you before he vanishes from the game entirely. [[spoiler:Until you make it to the Judgement Hall, where, after giving you one last chance to turn back, makes good on his warning and initiates battle with you. You'll probably find yourself wishing you had listened]].

** With the little info on his backstory, the only clear part is that Sans wasn't always a "lazybones". For a long time, he did his best to "fix" [[spoiler:the broken machine in his basement; possibly to bring back people he lost and by extension, to get to the surface. Unfortunately, the machine can not be fixed according to WordOfGod and Sans has no power to stop the resets]]. By the time you meet him, he's already resigned to [[EternalRecurrence his fate]] and doesn't care about [[spoiler:going to the surface or seeing his lost loved ones anymore.]]
** This is the main point of his "Special Attack", where he decides to [[spoiler:not end his turn, intending to bore you into quitting the game.]]

* LastStand: His boss fight. Sans knows that [[spoiler:your power to reset]] means that he can't beat you. But after seeing all the death left in your wake, knowing that you'll go on to [[spoiler:destroy the entire world]], and that there's no one else who can fight you, he decides he can't afford to not care anymore. Sadly, despite his best efforts to get you to give up, [[spoiler:his laziness ends up costing him his life.]]
* LazyBum: [[ZigZaggedTrope Zigzagged]], despite being one of his most obvious character traits. While in most runs, he's so apathetic as to be barely mobile, he puts more effort into stopping you than anyone but Undyne on [[spoiler:a Genocide run]]. It's also implied that [[spoiler:he busted his ass in the past to try and solve his world's problems through time and space before he realized it was simply impossible]], resulting in his current depressed, hopeless state. That being said, he admits that he might just be using depression as an excuse for his faults, and his lack of energy ends up [[spoiler:killing him regardless when he falls asleep, allowing the player to finish him off.]]

* LethalJokeCharacter: Sans is described as the easiest enemy who can do only a single point of damage per hit. As it turns out, what this really means is [[spoiler:1 ATK ''per frame''.]] And boy, does he take advantage of this to the extreme. Not only does he attack at ridiculous rates and in ridiculous amounts, but also, [[spoiler:the 1 ATK means his attacks pierce MercyInvincibility to deal constant damage and leaving a poison effect.]] And they're some of the most ''intense'' in the entire game, because of the speed and range of his attacks (in some cases, there's literally just one tiny spot in the box where you can hide). [[spoiler:He leaves his 1 defense point moot by constantly dodging your one hit kill swings.]]

* ManChild: Not nearly to the extent of his brother, but he definitely has shades. On top of having a very goofy sense of humor, his work ethic, cleaning habits, and general lifestyle are all reminiscent of a lazy, irresponsible teenager. Unlike Papyrus, however, this has a lot less to do with his actual maturity level and lot more to do with him [[spoiler:having [[StoppedCaring very little motivation in life to do much of anything]] due to a ''lot'' of unresolved emotional baggage]]

* MediumAwareness: Sometimes breaks the fourth wall as part of a gag. He knows ''much'' more than he lets on, however. For instance, he's aware that [[spoiler:a God-like being he has no hopes of meaningfully communicating is manipulating and reseting reality at will.]] This is the reason why he's so apathetic and lazy -- [[spoiler:the only alternative he can see is living in constant paranoia that the world will reset at any moment.]] He's also aware of how battle structure works [[spoiler:and tries defeating you by prolonging his turn, denying you your turn.]]

* MetaphoricallyTrue: His stat readout lists him at [[spoiler:1 attack and 1 HP]]. And while that is technically true, he not only ''refuses'' to let your attacks land, but his attacks [[spoiler:continually deal 1 HP for every instant their hitboxes make contact with you ''and'' apply a poison effect that ticks down at -- you guessed it -- 1 damage per frame.]]

* MinoredInAssKicking: Sans would very much prefer to [[TheSlacker sit around and make jokes all day]], only stepping into your adventure once in a while to share food or friendly advice with you, but if pushed far enough, [[spoiler:[[UpToEleven Sans becomes the single most dangerous monster in the underground.]]]]

* MyRulesAreNotYourRules: Sans [[spoiler:can break the rules of the entire game by ignoring your MercyInvincibility, randomly jumping from attack to attack, dodging (which is something other characters can't do), and killing you when you accept his offer to [[ISurrenderSuckers spare him]].]]

* NonchalantDodge: Sans can [[spoiler:sidestep your attacks]], and wonders why no one else tries it... But then it's subverted to disturbing effect when [[spoiler:the Fallen Child takes over [[DiagonalCut and slices him in two despite his attempts to dodge.]]]]

* NoSell: Sans' battle is designed so that none of your equipment will give you an edge--[[spoiler:not even the [[InfinityPlusOneSword Real Knife]] or [[ArmorOfInvincibility the Locket]]--as he dodges every one of your immensely powerful attacks and pierces your defense via DeathOfAThousandCuts. You ''can'' still get healing boosts from the Burnt Pan and Stained Apron or gain a slight few MercyInvincibility frames from the Torn Notebook and Cloudy Glasses, but it doesn't count for much.]]

** While he does have a subtle emotional range throughout the entire game, the one and only time where he truly and genuinely loses his cool is near the end of [[spoiler:his boss fight. Should you survive his penultimate attack, he, in a fit of what is clearly rage and/or desperation, turns your SOUL blue and begins slamming it around the battle box like a child flinging around a toy, a stark contrast from the quick-but-controlled way he'd been fighting the entire battle.]]

* ObfuscatingStupidity: Sans appears to be a regular goofball -- [[spoiler:unless you take the No Mercy route, where he threatens you and challenges the player to an ''extremely difficult'' boss battle.]] In addition, the contents of his workshop and his {{Offscreen Teleportation}}s imply he's a quantum physicist with a working time machine, who has a working knowledge and connection with the space-time continuum in-game.

* OneHitKill: Partway through the fight, Sans will offer [[spoiler:to spare you.]] This is a trap; if you accept this offer, Sans will [[spoiler:fill up the combat box with bones arranged in a jail-cell pattern that ''can't be dodged'', taking off all your health and resulting in a game over.]]

** Sans is almost always cracking wise or lazing about, seemingly without a care in the world. Yet he has his moments of gravity, and when it comes time to deliver them, [[GameFace his pupils fade into darkness]], his VoiceGrunting disappears (often taking the background music with it), and he loses his AllLowercaseLetters speaking style. He even changes fonts (he usually speaks in Comic Sans, but switches to the sans-serif 8bitoperator for his serious lines). Also, if it's your fault that Sans finally decides to [[LetsGetDangerous stop being lazy]], well... [[ThisIsGonnaSuck you're gonna have a bad time.]]
** Also, he avoids hard work, even if you kill all the leaders... but his love for his brother is stronger than his sloth. [[spoiler:If Papyrus becomes king, Sans will work really hard for him.]]
* OrphanedSetup: Due to coding error, some of his [[HaveANiceDeath lines]] [[spoiler:from No Mercy]] in the earlier versions of the game didn't have the intended punchline, as below (the missing parts are in bold) .

* PaintingTheMedium: To start, Sans speaks in comic sans. Secondly, he spends most of the game talking in AllLowercaseLetters... but at random he'll leave his I's capitalized, and he will sometimes use apostrophes correctly but sometimes won't. Yes, Sans is so lazy he can't even use AllLowercaseLetters consistently. Or to put it another way, Sans speaks like he's ''typing'' but is too lazy to type properly; now remember that Toby Fox had to type all of Sans' dialogue.
* PayEvilUntoEvil: During his fight in a [[spoiler:Genocide run]]. By this point, [[spoiler:you've basically committed mass-slaughter and killed Papyrus who wasn't fighting and wanted to help you.]] Sans puts you through absolute hell, without hesitating to cheat and play unfairly, [[spoiler:even faking a spare.]]

* PintsizedPowerhouse: He's about as tall as the Child, [[spoiler:and is undeniably one of the strongest bosses in the game.]]

* PreAssKickingOneliner: [[spoiler:"it's a beautiful day outside. birds are singing, flowers are blooming... on days like these, kids [[KidsAreCruel like you]]... '''[[ThisIsUnforgivable Should be burning in hell.]]'''"]] This is even played with to mess with you even further -- he'll cut the speech off mid-sentence and immediately jump into his opening routine entirely at random.

* ReasoningWithGod: You, the player, are effectively the god of the world of ''Undertale'' and are treated as such in-universe. In battle, [[spoiler:Sans reaches out to you personally and pleads with you to call off your current playthrough, reminding you that you were once friends.]]
* TheReasonYouSuckSpeech: Delivers one to the player in the second stage of his battle, questioning why they want to destroy his world so badly. [[spoiler:Given that this happens after his attempts to stop the player through trickery and just plain making the battle difficult have failed, doubles as an attempt to BreakThemByTalking.]]

* RetiredBadass: Setting aside the question of [[spoiler:just how in the world he got to be such a badass, the game also strongly implies he used to be a ScienceHero of sorts. He even has a badge of some sort lying around in his secret room, suggesting his role was official to some degree.]]
* RightForTheWrongReasons: He's correct in that you, as the Anomaly, are [[spoiler:causing timelines to reset]], given that the player's likely gotten the Neutral and Pacifist endings before going down the Genocide route (never mind SaveScumming). However, Sans has no idea about Flowey's actions prior to the player's intrusion into events, meaning [[spoiler:he's accusing you of ''all'' the prior resets that induced his apathy in the first place as well.]]
* RippleEffectProofMemory: Although most characters in the game have a severely downplayed example of this, only allowing them to retain subconscious, deja-vu-esque memories from previous timelines that serve no practical purpose, Sans took it a step further by [[spoiler:apparently training himself to read people on a borderline-Orwellian level. Just by studying your facial expression, he can make a number of accurate guesses as to what you've been up to in your previous playthroughs, including if you ever had the nerve to kill his brother.]] He never reveals the full extent of this ability unless you make it to [[spoiler:the final battle with him, where he's able to, among other things, keep track of the exact number of times you've died up to your ''eleventh'' attempt just by glancing at your face.]]

** Alluded to when facing him as a Lost Soul, and explicitly stated [[spoiler:when fighting him on a No Mercy run]]. His knowledge of [[spoiler: the player's and Flowey's interference with the timeline (through saving and resetting), and the belief that things will inevitably be reset again in the future]], has left him exhausted and existentially depressed. It's implied that this also has something to do with the strange machine Sans is working on...
** Sans also displays a degree of self-loathing, most notably in the ending where [[spoiler:you kill all of the important characters and at least one other monster, leaving the Underground utterly bereft of leaders]]. Sans talks about why he didn't take up the throne and explains that it isn't his style, and that he prefers to take things easy... before explaining that that was a joke and the whole mess they're stuck in is exactly what happens when "people like [him]" take it easy.

* SealedEvilInADuel: Attempted. [[spoiler:His 'Special Attack' is simply to start his turn... and never end it]]. He outright says that he intends to just sit there until you get bored and turn off the game. [[spoiler:Unfortunately, he falls asleep after a while, allowing you to finally kill him.]]

** While Flowey has been pushed to being one, Sans has a lot of icon power on the internet, to the point where people who have only glanced at Undertale but never played it can probably recognize what game he's from when they see him elsewhere. Tends to happen when you're one of the most liked characters [[spoiler:and a freakishly difficult and memorable BonusBoss, which is verging on ItWasHisSled in most circles.]]

* ShaggyDogStory: Sans firmly believes [[spoiler:his life is a big one due to resets and his mysterious failures to "go back", and excuses his laziness to his awareness of this fact.]] He is not completely wrong, although [[spoiler:it is possible for you to finally put an end to it either by abstaining from a True Reset after completing a Pacifist run or by [[ShootTheShaggyDog shooting his dog]] by playing a Genocide run.]]
* SheatheYourSword: What his special attack turns out to be -- [[spoiler:he just never ends his turn, meaning ''you'' never get ''yours'', unless you find a way to cheat the system.]]

** His opening attack, which is a string of [[spoiler:extremely powerful attacks and, more importantly, ''goes before your first turn''.]]

* SmugSmiler: One of the better tropes one could use to describe his default attitude. While it's usually a lighthearted example to emphasize his status as TheGadfly and a DeadpanSnarker, it takes a turn for the [[GrinOfAudacity deadly]] should you manage to [[spoiler:drive him to the point of having to fight you.]]
* TheSocialExpert: Most would consider him to have the most normal social etiquette of any character in the game, and he is very popular with the other residents of Snowdin. Pretty much everybody knows him by name and his mailbox is always jam-packed. Taken to the extreme when it's revealed in the Genocide route that he [[spoiler:can read people so well he can practically read their minds, all the way down to extremely nuanced detail.]]

-->'''Sans''': hey, [[SincerityMode i really respect what you did back there. thanks.]]

* SourSupporter: Part of what's BeneathTheMask, Sans is very good at hiding this side of him throughout the Pacifist route. He sort of implies his disbelief towards the protagonist's desire to get back home during his dinner date, but it's not until the last minute that we understand the extend of his [[DespairEventHorizon cynicism]]. And this is if you didn't kill his brother; if you dare to kill Papyrus, [[HeroicBSOD he disappears from the game entirely]], and if you didn't invoke a Genocide run, the only support you'd ever get from him would be [[spoiler:not being brutally murdered by him.]]

** He's also this trope offensively: his final move before his special attack is a [[NoHoldsBarredBeatdown brutal beatdown]] who only takes 1 HP per hit until your character only has 1 HP left. After that, his moves only smash you on the walls without any effect.

** During normal gameplay, there are many small hints that by themselves wouldn't mean much, but taken altogether, paint a bleak picture of his everyday life; he overeats unhealthy comfort food, sleeps far too much, puts bare minimum effort into his work, has very few close friends despite appearing popular, and may or may not be a regular drinker. None of this is surprising on the surface -- it's just the sort of thing a lazy slob like him would do -- but when you contextualize it with the little information we're given on his backstory and the fact that [[spoiler:he's living with the knowledge that his life is a GroundhogDayLoop where nothing really matters and he'll never get the chance to move forward]], and it goes from being amusing to a pretty obvious implication of depression. Exactly how much this affects him varies depending on how the player affects the world, how hopeful things seem, and personal interpretation on the player's part. [[spoiler:Even on the best possible path, he has enough awareness of just how easily things can be turned back that it's very likely he'll be fighting an uphill battle to become his old self once he's living on the surface.]]

* StoppedCaring: He doesn't seem to care about anything aside from bad jokes and his brother. [[spoiler:He's figured out that someone or something has been resetting and manipulating the timeline, and has given up trying to stop them... aside from befriending everyone he meets in the hope that one of them is the source and he can finally make them contented enough to stop]].

* SurvivorGuilt: There's vague but plausible breadcrumbs of evidence within the game that, when strung together, suggest that [[spoiler:he's the only survivor of some great catastrophe that either killed or permanently separated him from the people featured in his scrapbook, contributing to the cynicism and self-loathing he lives with today.]]
* SymbolicBlood: When he's [[spoiler:killed at the end of a Genocide Run]], a red liquid that ''looks'' like blood starts dripping from his wound. However, it's been clearly established that monsters don't bleed when they die, and simply turn to dust. Because of this, it's unlikely that the substance is actually blood (unless Sans [[AmbiguouslyHuman isn't really a monster]])--it might be ketchup.

* ThatOneBoss: In-universe; according to Flowey, whose sociopathy and [[spoiler:ability to SAVE]] drove him to start treating the Underground like an RPG, [[spoiler:Sans caused him "more than his fair share of resets." He's likely to do the same to you in a Genocide run.]]

* ThisLooksLikeAJobForAquaman: His stats are the worst of any monster in the game, ''including a literal child'', and he can only deal 1 damage to the player with each attack. Howevever, [[spoiler:his [[DamageOverTime special ability]] being called [[{{Karma}} KR]] seems to imply that he is specifically effective against the player at the end of the No Mercy Run ''[[CreateYourOwnHero because]]'' of all the LOVE collected before fighting him.]]

* TookALevelInCynic: [[spoiler:After Flowey's constant resets]], Sans lost the passion he once had. He also has a broken machine in his basement that according to WordOfGod can not be repaired, no matter the amount of hard work Sans put in to fix it. One can only imagine the pain he went through to get to the point of [[StoppedCaring not caring about anything anymore.]]

* TrademarkFavoriteFood: He seems to like ketchup a lot--we see him down a whole bottle of it at Grillby's, and he keeps a container of it at his sentry station (along with other condiments like mustard and relish). [[spoiler:It's possible that the SymbolicBlood leaking from his body after you kill him is also ketchup, since it has the exact same color.]]
* TragicDream: We don't know exactly why, but he really, ''really'' wants [[spoiler:that machine in his secret room fixed.]] Sadly, WordOfGod has stated that this will never happen, and he's long given up even trying anymore.
* TranquilFury: Sans, of course, is a very chill skeleton... and the most chilling thing about him is his no-nonsense font and lightless sockets if you manage to piss him off. Taken UpToEleven during [[spoiler:the final battle with him, where he's ''still'' grinning with one hand in his pocket as he ''pulverizes'' you with the other one, one of his eyes literally flashing with rage.]]

* {{Troll}}: Screwing with people is pretty much his M.O, and since it's normally [[TheGadfly in good nature]], one of the more subtle ways he lets you know that you've [[TranquilFury pissed him off]] is when he starts taking a page from this trope. One of the best (and arguably most hilarious) instances of this is during [[spoiler:his boss fight, should you accept his offer of mercy (and get hit with the subsequent -- and completely unavoidable -- OneHitKill attack).]] The "Game Over" music will be replaced with a sped-up version of the goofy "Dog Song" track as Sans mocks you. Reload the game and talk to him again and he'll mention how incredibly pissed off you look.

* WalkingSpoiler: There's quite a bit more to Sans than just the joke-loving skeleton you meet early on. Those avoiding spoilers take heed: even glancing at fanart of Sans will almost certainly give away something about his character. And, y'know, there are a lot of spoiler marks here for a reason. [[spoiler: To sum up, Sans is one of the two {{Fourth Wall Observer}}s, '''the''' FinalBoss of the [[KillEmAll Genocide Route]] plus [[WakeUpCallBoss how]] [[ISurrenderSuckers he]] [[OffscreenTeleportation fights]], and the fact [[IWarnedYou he warns you if you win]] that it's the PointOfNoReturn.]]

* WeakButSkilled: Technically speaking, he really is the weakest enemy in the game, having only 1 HP and only capable of doing 1 damage. He makes up for it through clever abuse of game mechanics. [[spoiler:He only has 1 HP, but he dodges all of your attacks instead of just taking them like every other monster in the game. His 1-damage attacks don't trigger the MercyInvincibility, so he does 1 damage ''per frame''. That's not even getting into his [[ISurrenderSuckers SPARE trick]], or his "special attack". Indeed, the only reason you can even kill him is by breaking the rules yourself -- dragging your SOUL over to the ATTACK button ''during his turn.'']]

** [[spoiler:''"LOVE, too, is an acronym. It stands for '''Level of Violence'''."'']] - Near the end of the game, Sans reveals that [[spoiler:the EXP and LV stats]] refer to something ''much'' different than in other games. [[spoiler:EXP stands for "execution points" and quantifies the pain you've inflicted on monsters, while LV/LOVE stands for "Level of Violence" and measures how easy it is to kill them.]] The one hint of this being the case happens early in the game and is easy to miss, so Sans spelling it out at the end can easily come out of left field.

* WideEyesAndShrunkenIrises: The lights in his eyes become very small pinpricks of white [[spoiler:after you mortally wound him.]]

* WorldsBestWarrior: There is not a soul in the Underground more deadly than the short, goofy pun-lover. Sure, he might be the physically weakest monster there, [[spoiler:but he'll essentially ''break reality'' to take you down.]]

* WowingCthulhu: Very few things even remotely faze the protagonist during the Genocide route, let alone impress or frighten them. [[spoiler:Sans is one of those things.]] He's also the one and only character [[spoiler:Flowey]], out of fear, respects on any level aside from [[spoiler:the Fallen Child.]]

* YankTheDogsChain: In a No Mercy run, he reveals that his apathy stems from a fear of this trope, because [[spoiler: he knows that any happy ending can be undone by the player resetting]].
-->'''Sans:''' you can't understand how this feels. knowing that one day, without any warning... [[spoiler: it's all going to be reset. look. i gave up trying to go back a long time ago. and going to the surface doesn't really appeal anymore either. 'cause even if we do... we'll just end up back here without any memory of it, right?]] to be blunt... it makes it kinda hard to give it my all.

* YouHaveResearchedBreathing: He's the only character in the entire game who even makes an attempt to [[spoiler:dodge your attacks. Sure, by that point in the game you're evil incarnate and could kill anything you want with a single blow, but you're still a small child wielding a kitchen knife (or whatever the Child has equipped) -- jumping out the way shouldn't be rocket science.]] Sans even [[LampshadeHanging smugly points this out]], which makes sense given his [[spoiler:awareness of other mechanics in the game]].
* ZenSurvivor: Sans knows a lot he's not letting on, borne from [[DarkandTroubledPast hard experience]], but knowing that telling you won't do any good, he masks this and acts to guide you in oblique aways while seeming apathetic to everything.

* FoolishSiblingResponsibleSibling: He manages to be both with Papyrus; in terms of superficial maturity, he's the foolish, but in terms of ''[[HiddenDepths actual]]'' [[HiddenDepths maturity]], he's the responsible.

[[Characters/UndertaleMainCharacters Major]] ([[Characters/UndertaleTheHumanChild The Human Child]], [[Characters/UndertaleFlowey Flowey]], [[Characters/UndertaleTorielAndAsgore Toriel]], ''Sans'', [[Characters/UndertalePapyrus Papyrus]], [[Characters/UndertaleUndyne Undyne]], [[Characters/UndertaleAlphysAndMettaton Alphys]], [[Characters/UndertaleMettaton Mettaton]], [[Characters/UndertaleAsgoreDreemurr Asgore Dreemurr]])\\

[[Characters/UndertaleMainCharacters Major]] ([[Characters/UndertaleTheHumanChild The Human Child]], [[Characters/UndertaleFlowey Flowey]], [[Characters/UndertaleTorielAndAsgore Toriel and Asgore]], '''Sans''', [[Characters/UndertalePapyrus Papyrus]], [[Characters/UndertaleUndyne Undyne]], [[Characters/UndertaleAlphysAndMettaton Alphys and Mettaton]])\\

* SquishyWizard: Taken UpToEleven with Sans, who has 1 attack, 1 defense, and [[OneHitPointWonder 1 HP]], but who uses convoluted magical attacks with no MercyInvincibility to compensate.

[[Characters/UndertaleMainCharacters Major]] ([[Characters/UndertaleTheHumanChild The Human Child]], [[Characters/UndertaleFlowey Flowey]], [[Characters/UndertaleAsgoreDreemurr Toriel and Asgore]], '''Sans''', [[Characters/UndertalePapyrus Papyrus]], [[Characters/UndertaleUndyne Undyne]], [[Characters/UndertaleMettaton Alphys and Mettaton]])\\

[[Characters/UndertaleMainCharacters Major]] ([[Characters/UndertaleTheHumanChild The Human Child]], [[Characters/UndertaleFlowey Flowey]], [[Characters/UndertaleAsgoreDreemurr Toriel and Asgore]], '''Sans''', [[Characters/UndertalePapyrus Papyrus]], [[Characters/UndertaleUndyne Undyne]], [[Characters/UndertaleMettaton Mettaton]])\\

[[Characters/UndertaleMainCharacters Major]] ([[Characters/UndertaleTheHumanChild The Human Child]], [[Characters/UndertaleFlowey Flowey]], '''Sans''', [[Characters/UndertalePapyrus Papyrus]], [[Characters/UndertaleUndyne Undyne]], [[Characters/UndertaleMettaton Mettaton]], [[Characters/UndertaleAsgoreDreemurr Asgore Dreemurr]])\\

!![[center:[-''[[Characters/{{Undertale}} Main Character Index]]''-]]][[center:[-[[Characters/UndertaleMainCharacters Major]]-] ([-[[Characters/UndertaleTheHumanChild The Human Child]]-], [-[[Characters/UndertaleFlowey Flowey]]-], [-Sans-], [-[[Characters/UndertalePapyrus Papyrus]]-], [-[[Characters/UndertaleUndyne Undyne]]-], [-[[Characters/UndertaleMettaton Mettaton]]-], [-[[Characters/UndertaleAsgoreDreemurr Asgore Dreemurr]]-]) | '''[-[[Characters/UndertaleOtherCharacters Minor]]-]''' | [-[[Characters/UndertaleMonsterEncounters Monsters]]-] | [-[[Characters/UndertaleSpoilerCharacters Spoilers]]-] ([-[[Characters/UndertaleTheFallenHuman The Fallen Human]]-])]]

[[caption-width-right:162:''"i've gotten a ton of work done today. a [[PungeonMaster skele-ton]]."'']]

* AlmightyJanitor: He's the Snowdin Forest watchman who is perfectly fine with shirking his duties and moonlighting with several other money-making schemes. He has [[OneHitPointWonder 1 HP]] and his attacks can only do 1 damage. [[spoiler:He also has a ''working knowledge'' of quantum physics, has figured out the timeline is being manipulated ''without'' a fully RippleEffectProofMemory, and is effectively TheDragon to Asgore. Oh, and those stats? His attacks ignore MercyInvincibility and apply a DamageOverTime effect, and he can ''dodge'' incoming attacks. IN SLIPPERS.]]

* TheDragon: To Papyrus [[spoiler:and Asgore]].
* DragonInChief:
** Heroic example. Papyrus, [[spoiler: Asgore]] and Sans are all immensely strong, but Sans is both exponentially stronger ''and'' smarter than both of them. Sure, [[spoiler: Asgore showers us with a BulletHell that's difficult to dodge]], and Papyrus is described by Undyne as "pretty freakin' tough" and shows that during his boss fight, but Sans ''[[RealityWarper breaks the rules of the game]]'' by [[spoiler: ignoring your MercyInvincibility, by [[SuddenGameplayChange turning the thing into a platformer]], and by evading your attacks.]]
** A more obvious example between him and Papyrus, though this relationship is more PlayedForLaughs than Sans' relationship with Asgore. Granted, Papyrus tends to do most of the work and probably only puts Sans to work due to his increasing laziness. See Papyrus' AngerBornOfWorry entry.

** [[spoiler:He's also one to Flowey. See GoodCounterpart for further explanations.]]

* HardWorkHardlyWorks: Papyrus constantly tries his best to join the Royal Guard while Sans just mostly slacks off. [[spoiler:Yet Sans is by far the stronger of the two brothers. Subverted. The reason Papyrus is having a hard time joining the Royal Guard is not because his lack of strength, but because of his unwillingness to fight seriously. As for Sans himself, his knowledge of the fact that everything is just going to be reset no matter how much he tried in the past is the reason for his laziness. In addition, he has caused Flowey 'more than his fair share of resets' in the past, meaning he used to be a hard worker. Double subverted in the Genocide run because no matter how many tricks he uses during his fight, he'll still lose in the end unless you RageQuit.]]

* GroundhogPeggySue: Sans is an odd case; [[spoiler:he's aware of being stuck in a time loop and is very alert to when a reset happens, but he carries over little to no memories of previous timelines to the present day. During a Pacifist run, all he can do is to play the role of a funny PungeonMaster so you could have a satisfying experience with the game and stop the resets for good once you reach the GoldenEnding. ''[[ThatOneBoss If you decide for a Genocide run, however...]]'']]

* HorrifyingTheHorror: [[spoiler:Both Flowey and The Fallen Child]] dread the moment Sans gets serious.
-->'''[[spoiler:Flowey]]:''' Say, if I have ONE piece of advice for you... DON'T. Let (Sans). Find out ANYTHING about you. He'll... well... Let's just say. He's caused me more than my fair share of resets. Stay away from him.
-->"You feel like you're going to have a bad time".

* LeaningOnTheFourthWall: More than a bit MediumAware. [[spoiler:He uses this to full effect when denying you your turn in the battle against him, thus denying you the ability to actually progress through the game. Also extended to how he treats your reloads, which he seems to observe from an in-universe perspective. While Flowey is actively aware of how you handle the timeline and abuses savestates to skip around, Sans seems to treat your different loads as alternate timelines and simply skips forward in battle without any visible justification. The main method of figuring out you've reloaded? Not through hard evidence, but simply recognizing how you react to different things. "That look on your face...it means something."]]

* BodyguardingABadass:
** Averted. He becomes Mettaton's bouncer/agent in the [[spoiler:King Mettaton Neutral ending]]. While on paper, Sans is the weakest monster, [[spoiler:his combat abilities outclass anyone else's]]. It is left vague if Mettaton knows this.
** Played straight [[spoiler:to the player. While Sans is powerful and [[ThatOneBoss hard to defeat]], he is technically less powerful than you because if he dies, he remains dead without your intervention. You, however, are immortal and every time you die, you are sent to the last save point so you can try again. That doesn't stop him from trying to protect you because of the promise he made to Toriel.]]

* MediumAwareness: Sometimes breaks the fourth wall as part of a gag. [[spoiler:He knows ''much'' more than he lets on, however; for instance, he's aware that a God-like being he has no hopes of meaningfully communicating is manipulating and reseting reality at will. This is the reason why he's so apathetic and lazy -- the only alternative he can see is living in constant paranoia that the world will reset at any moment. He's also aware of how battle structure works and tries defeating you by prolonging his turn, denying you your turn.]]

** [[spoiler:''"You'd be dead where you stand."'' - referencing that if Toriel hadn't asked him to leave you be, he would've instantly killed you the moment he saw you.]]

** Amusingly, they both have different opinions on Let's Players and their audience. [[spoiler:In the No Mercy run, Flowey calls the audience of Let's Players cowards and sickos for wanting to watch the Genocide route without doing it themselves. In the Neutral and Pacifist routes, specifically on the Xbox edition [[ItMakesJustAsMuchSenseInContext inside Papyrus' sink]], Sans, ever the lazybones, asks why you wouldn't just watch a video of the "exclusive [Xbox] game" instead of playing it yourself.]]

** Amusingly, they both have different opinions on Let's Players and their audience. In the Genocide route, Flowey calls the audience of Let's Players cowards and sickos for wanting to watch the Genocide route without doing it themselves. In the Neutral and Pacifist routes, specifically on the Xbox edition [[ItMakesJustAsMuchSenseInContext inside Papyrus' sink]], Sans, ever the lazybones, asks why you wouldn't just watch a video of the "exclusive [Xbox] game" instead of playing it yourself.