Sans/In battle

For the fight with Sans in the 10th Anniversary Stream, see Sans/In battle (10th Anniversary).

it's a beautiful day outside.
birds are singing, flowers are blooming...
on days like these, kids like you...
Should be burning in hell.

Sans

Sans is the final boss of the Genocide Route. Similarly to the Neutral Route and the True Pacifist Route, he awaits the protagonist at the Last Corridor. However, he forgoes judgment, apologizes to the now-deceased Toriel, and begins an encounter.

Sans alters the SOUL mode to red or blue, and uses white and light blue Attack Types. He attacks with bones in complex patterns, straight beams from "Gaster Blasters", and telekinesis. Excluding telekinesis, Sans's attacks inflict KARMA, which dwindles the protagonist's HP over time.

The battle with Sans is one of the battles where Serious Mode is enabled.

Attacks

SOUL modes

Excluding the first attack, Sans sets the SOUL to blue mode for the first half of the battle. At the halfway point, Sans also occasionally swaps to red mode, after which he uses a mix of red and blue.

Patterns

Sans's attack style is focused on platforming, spontaneity, and forcing quick decisions. Unlike other battles in Undertale, Sans always attacks first at the start of the battle.

Strongest attack

All segments of Sans's "strongest" attack.

There are three segments for the intro attack:

1. Sans activates blue mode and throws the SOUL to the bottom of the bullet board. A red rectangle indicator appears at the bottom, and shortly after, bones rise and cover the area.
2. The SOUL turns red, and a wave of bones appears from the left side of the board. These bones cover the top and bottom of the board and has a somewhat linear gap between them.
3. Sets of Gaster Blasters appear to shoot beams 4 times:
   • Four shoots and covers the sides of the bullet board.
   • Four that shoot from the corners of the board, making the beams appear as an "X" pattern.
   • A replica of the first, which covers the sides of the board.
   • Two large Gaster Blasters emit large beams from the left and right side of the bullet board. The beams cover nearly the entire board except the top and the bottom.

First phase

Sans's first phase lasts until the protagonist's 13th attack. Sans uses the following attacks in order for his first phase. Blue SOUL mode is active for all of these attack turns.

If Sans has exhausted these attacks before he attempts to offer mercy, he chooses an attack at random. The attacks he chooses consist of harder versions of Bone Gap and Platforms 4, Randomized Bone lines, Horizontal bone slides, and Platform Blasters.

Turn no.	Attack	Information	Hard variant
1	Bone Gap	16 lines of bones with a small gap between them, for a total of 8 small jumps. The lines appear from the left and right, and are made of small bones at the bottom, and long bones at the top of the bullet board.	The bone lines appear sooner.
2	Blue Bone	12 sets of bones: 6 appear from the left side of the board, then 6 appear from the right. The left side's pattern is a long light blue bone, then a short bone. The right is short bone, then long light blue bone.	-
3	Randomized bone lines	Randomized pairs of bone lines appear from the left and right, and can appear at varying speeds. These force the SOUL to jump at varying heights through the gaps, which can range from 3 - 6 jumps.	-
4	Platforms 1	Starting from the left is three green rectangle platforms atop a sea of bones. Near the top of the third platform is a set of three bones, and at the end of the sea of bones is a long bone from the top.	-
5	Platforms 2	Starting from the right is a longer platforming segment with seven green platforms. The fourth, fifth, and sixth platforms have a bone above each platform. The last platform has long bones appearing from the top left and bottom right sides.	-
6	Platforms 3	A segment with moving, long green platforms and bones that can block a path. The bottom platforms appear from the right, and the higher platforms appear from the left.	-
7	Platforms 4	The SOUL appears on a small green platform that moves left, then right. The bottom of Board is covered by a sea of bones, and three sets of bones move vertically near the center. The center line of bones descends, while the outer two lines rises.	More bones appear for the outer lines of rising bones, which have a smaller gap to jump through.
8	Horizontal bone slides	Sets of small bones appear on the bottom, from the left, and large bones appear at the top, from the right.	-
9	Platform Blaster	A segment with small moving green platforms and has thin Gaster Blasters. The bottom platforms appear from the right, and the top appear from the left. The thin Gaster Blasters appear from the left or right sides to shoot above or below platforms.	The Gaster Blasters appear sooner.

False mercy

Sans pauses the battle and attempts to show the protagonist mercy. If accepted, he covers the entire bullet board with bones until the protagonist's HP is depleted entirely. Shortly after, the Game Over screen appears with the sped-up Dogsong playing in the background. Sans taunts the protagonist for their defeat and tells them not to come back if they really are friends. If the Game Over screen is not triggered, the bones eventually retract after enough time has passed, far past the point at which the protagonist's HP should have been reduced to 0, after which the game softlocks.

Second phase

Sans's second phase lasts until the protagonist's 23rd attack. Sans begins to launch attacks while the protagonist is navigating through the battle menu. These attacks cannot deplete their HP below 1.

• Initially, A small bone emerges from the left side of the screen, covering the top-left menu option.
• After the 16th attack, bones begin to slide across the action buttons.
• After the 18th attack, the two previous attacks are combined and occur at the same time.

Sans uses the following attacks, in order, for his second phase. Sans incorporates red SOUL mode more often during these attacks.

1. Screen flicker 1: Sans uses a series of short attacks while transitioning between them by flickering the screen. These attacks mostly use blue SOUL mode, with some exceptions. The attacks are as follows:
   • A massive wall of bones slides across the bullet board, just short enough for the protagonist to jump over.
   • Two walls of bones converge to the center of the bullet board from either side. The walls have a section short enough for the protagonist to jump over.
   • Two sets of bones converge to the center of the bullet board from either side. The sets consist of a light blue bone covering the height of the bullet board followed by two white bones, one short bone followed by another bone covering the height of the bullet board.
   • Two pairs of bone lines slide across the bullet board from opposite sides. Each line has a gap that the protagonist must jump through.
   • Two pairs of bone lines slide across the bullet board from opposite sides. Each line appears at varying speeds and has a gap of varying height that the protagonist must jump through.
2. Gaster Blaster barrage 1: Sans activates red SOUL mode and unleashes thin Gaster Blasters aimed at the SOUL from all directions.
3. Screen flicker 2: Sans uses a different set of attacks that he transitions through by flickering the screen:
   • Sans activates red SOUL mode, and a wave of bones appears from one side of the bullet board covering the top and bottom sides. The bones have a gap that the protagonist must go through
   • Sans activates red SOUL mode, and four Gaster Blasters fire at the center of the bullet board in an "X" or a "+" formation.
   • Two platforms are present above a row of bones covering the bottom side of the bullet board, and two bones covering the top and bottom platforms appear from the left and right. The SOUL appears on the top platform and must maneuver their way around the bones.
   • Sets of small bones appear on the bottom, from one side, and large bones appear at the top, from the other.
4. Directional wall slam 1: Sans activates blue SOUL mode and continuously slams the SOUL onto one of the walls of the bullet board. Each time the SOUL lands, bones rise up and cover the wall. The SOUL must jump in the opposite direction of the wall to avoid the bones.
5. Directional wall slam 2: The interval between slams is shorter, allowing less time to avoid the bones that rise up.
6. Gaster Blaster barrage 2: Sans activates red SOUL mode and unleashes thicker, yet slightly slower, Gaster Blasters aimed at the SOUL from all directions.
7. Vertical bone lines: Sans activates red SOUL mode, and bones scroll vertically down the left and right sides of the bullet board, meeting at the center.
8. Screen flicker 3: Sans combines the sets of attacks from "screen flicker 1" and "screen flicker 2".
9. Directional wall slam 3: The area that the bones cover is significantly larger, and the time given to jump is much shorter.

If Sans's final attack is not triggered at this point, he repeats "Gaster Blaster barrage 2", "directional wall slam 3", and "screen flicker 3" at random.

Final attack

After the 23rd attack, Sans unleashes his final attack. It is comprised of the following segments.

1. Four repetitions of "directional wall slam 3"
2. A short snippet of "vertical bone lines"
3. Sans slams the SOUL against the left side of the bullet board and extends the right side far past the edge of the screen. As the SOUL falls to the right, a wave of bones scrolls across the bullet board, followed by sets of three bones across the top and bottom, then two rows of bones that close in onto the center. Once the SOUL reaches the right edge of the bullet board, a row of bones rises up to cover the area.
4. Sans flickers the screen and launches four sets of attacks, all consisting of rows of bones rising up to cover certain walls of the bullet board.
   1. Two rows of bones covering the top and bottom, with the SOUL appearing at the bottom
   2. Two rows of bones covering the left and top, with the SOUL appearing at the top left and resting on the top wall
   3. Two rows of bones covering the bottom and right, with the SOUL appearing at the bottom right and resting on the right wall
   4. A row of bones covering the left side, with the SOUL appearing at the top left and resting on the left wall
5. The SOUL turns red, and Gaster Blasters continuously circle the bullet board and fire at the center. The Gaster Blasters form five full circles before the attack ends.

After this, Sans repeatedly slams the SOUL against random walls of the bullet board. The protagonist's HP is depleted by 1 for every slam but stops once their HP reaches 1.

"Special attack"

Sans defeated.

Once the protagonist survives his final attack, Sans uses his "special attack" - preventing the protagonist from accessing the menu by stalling indefinitely, in hopes for them to withdraw out of boredom. After Sans finishes talking, the protagonist must wait as his eyes gradually close, then slowly push the bullet board to the left and then downwards to access the "FIGHT" option. The bullet board cannot be pushed elsewhere, and should the protagonist try to push to the left before Sans closes his eyes, his left eye flashes light blue and yellow as he teleports the protagonist's SOUL back to the middle of the bullet board. This resets the time it takes for him to fall asleep.

When the protagonist's SOUL selects the FIGHT option, they attack Sans. He dodges the attack, but is struck down by an automatic second attack that deals 9999999 damage. Sans starts to leak a red fluid of some sort and, after one final warning, slowly limps off-screen before disintegrating into dust. This ends the fight, with the protagonist's LOVE being set to 20 and HP to 99.

Mechanics

Unlike other bosses, Sans dodges up to 24 attacks, resulting in a "MISS". This way, he negates a need for high defense or health.

Through KARMA (KR), Sans drains the protagonist's HP by 1 per frame, and can inflict multiple weak hits (up to 30) at a rapid rate. This effect is also active during the protagonist's turn. The amount of KR inflicted varies per attack type, and its duration depends on how much the SOUL was hit. However, the protagonist cannot be killed until the KR effect ends. The exception is the SOUL being damaged at 1 HP during one of Sans's KR-inflicting attacks. The protagonist's INV can slow down the effects of KARMA.

Some attacks involve rectangle platforms, which are green on the top and white on bottom. These can be seen outside of the bullet board. The SOUL can jump through the white portions of these platforms and rest on top of one.

After Sans pretends to spare the protagonist and fails, he also attacks with bones on the action menu. These bones deal 1 damage per hit, do not inflict KR, and cannot kill the protagonist.

Strategy

Pre-battle, consumables such as Legendary Hero, Snowman Piece, Steak in the Shape of Mettaton's Face, Instant Noodles, Butterscotch Pie can be kept. Due to KARMA's effects, it is beneficial to wait for the effect to end before using an item.

To progress the fight, the protagonist must keep attacking Sans, as Checking him hints that he cannot "keep dodging forever". Performing any other action besides FIGHT, including skipping/missing the attacks, does not progress the battle, as his dialogue does not appear or advance. Sans cannot be spared, as the only way to end the fight is for the protagonist to defeat him.

While most equipment is useless as DF does not affect Sans's constant 1 damage and AT does not affect his dodging, nor does it help the fact that he only has 1 HP and Defense, there are several exceptions:

• The Burnt Pan's boost to healing items can be very useful for the protagonist to recover health.
• If the protagonist has INV-boosting items equipped, such as the Cloudy Glasses and the Torn Notebook, damage is ignored every few frames, and KR drains slower.
  • Note: While the Stained Apron and Temmie Armor can heal 1 HP every other turn and the latter also boosts some INV, they are both unobtainable on the Genocide Route.

Sans does not attack the protagonist when he attempts to offer false mercy, which allows the protagonist to heal as many times as they need to.

Quotes

Pre-battle

• heya.
• you've been busy, huh?
• ...
• so, i've got a question for ya.
• do you think even the worst person can change...?
• that everybody can be a good person, if they just try?
• 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.
• welp.
• sorry, old lady.
• this is why i never make promises.
• [Refight]
  • heya.
  • you look frustrated about something.
  • guess i'm pretty good at my job, huh?
• [Refight #2]
  • hmm. that expression...
  • that's the expression of someone who's died twice in a row.
  • suffice to say, you look really... unsatisfied.
  • all right.
  • how 'bout we make it a third?
• [Refight #3]
  • hmm. that expression...
  • that's the expression of someone who's died thrice in a row.
  • ...
  • hey, what comes after "thrice," anyway?
  • wanna help me find out?
• [Refight #4]
  • hmm. that expression...
  • that's the expression of someone who's died quice in a row.
  • quice? frice?
  • welp, won't have to use it again anyways.
• [Refight #5]
  • hmm. that expression...
  • that's the expression of someone who's died five times in a row.
  • convenient, huh? that's one for each finger.
  • but soon...
  • you'll need a cool mutant hand to count all of your deaths.
• [Refight #6]
  • hmm. that expression...
  • that's the expression of someone who's died six times in a row.
  • that's the number of fingers on a mutant hand.
  • but soon...
  • you'll need to find a mutant hand with even more fingers.
• [Refight #7]
  • hmm. that expression...
  • that's the expression of someone who's died seven times in a row.
  • hey, that's good. seven's supposed to be a lucky number.
  • who knows, maybe you'll hit the jackpot...
  • and that number will multiply tenfold.
• [Refight #8]
  • hmm. that expression...
  • that's the expression of someone who's died eight times in a row.
  • that's the number of fingers on a spider.
  • but soon...
  • wait, don't spiders have legs?
• [Refight #9]
  • hmm. that expression...
  • that's the expression of someone who's died seven times in a row.
  • ...
  • nope, wait, that's definitely nine, sorry.
  • or was it ten?
• [Refight #10]
  • hmm. that expression...
  • that's the expression of someone who's died ten times in a row.
  • hey, congrats! the big one-oh!
  • let's invite all your friends over for a big shindig.
  • we can have pie, and hot dogs, and...
  • hmmm... wait. something's not right.
  • you don't have any friends.
• [Refight #11]
  • hmm. that expression...
  • that's the expression of someone who's died eleven times in a row.
  • well, give or take.
  • there's nuance to this stuff.
  • don't think i'll be able to count very well from here.
  • count for me, ok?
  • we'll start from 12.
• let's just get to the point. [Refight #12+]
• [Refight after killing Sans]
  • ...
  • that expression that you're wearing...
  • ...
  • well, i won't grace it with a description.
• [Refight after killing Sans two or more times]
  • ...
  • that expression that you're wearing...
  • ...
  • you're really kind of a freak, huh?

Battle

• [First time and only until the opening attack is survived once]
  • it's a beautiful day outside.
  • birds are singing, flowers are blooming...
  • on days like these, kids like you...
  • Should be burning in hell. [Sans's voice is not present for this line.]
  • [Opening attack plays]
  • huh.
  • always wondered why people never use their strongest attack first.
• [After surviving the opening attack once; abruptly cuts to the opening attack]
  • it's a beautiful day outside.
  • birds are singing,
  • [Opening attack plays]
  • anyway, as i was saying, it's a nice day out.
  • why not relax and take a load off?
• [After surviving the opening attack 2+ times]
  • ready?
  • [Opening attack plays]
  • here we go.
• [Attack #1] what? you think i'm just gonna stand there and take it?
• [Attack #2]
  • our reports showed a massive anomaly in the timespace continuum.
  • timelines jumping left and right, stopping and starting...
• [Attack 3] until suddenly, everything ends.
• [Attack #4]
  • heh heh heh...
  • that's your fault, isn't it?
• [Attack #5] you can't understand how this feels.
• [Attack #6]
  • knowing that one day, without any warning...
  • it's all going to be reset.
• [Attack #7] look. i gave up trying to go back a long time ago.
• [Attack #8] and getting to the surface doesn't really appeal anymore, either.
• [Attack #9]
  • cause even if we do...
  • we'll just end up right back here, without any memory of it, right?
• [Attack #10]
  • to be blunt...
  • it makes it kind of hard to give it my all.
• [Attack #11]
  • ... or is that just a poor excuse for being lazy...?
  • hell if i know.
• [Attack #12]
  • all i know is... seeing what comes next...
  • i can't afford not to care anymore.
• [Attack #13]
  • ugh... that being said...
  • you, uh, really like swinging that thing around, huh?
  • ...
  • listen.
  • i know you didn't answer me before, but... [Normal spare dialogue]
    • somewhere in there. i can feel it.
    • there's a glimmer of a good person inside of you.
    • the memory of someone who once wanted to do the right thing.
    • someone who, in another time, might have even been...
    • a friend?
    • c'mon, buddy.
    • do you remember me?
    • please, if you're listening...
    • let's forget all this, ok?
    • just lay down your weapon, and...
    • well, my job will be a lot easier.
  • friendship... [Spare dialogue if the protagonist has previously tried sparing Sans]
    • it's really great, right?
    • let's quit fighting.
  • [Spare]
    • ...
    • you're sparing me?
    • finally.
    • buddy. pal.
    • i know how hard it must be...
    • to make that choice.
    • to go back on everything you've worked up to.
    • i want you to know... i won't let it go to waste.
    • ...
    • c'mere, pal.
    • [Fight screen after getting betrayed by Sans] geeettttttt dunked on!!!
      • if we're really friends...
      • you won't come back.
• [Attack #14]
  • welp, it was worth a shot.
  • guess you like doing things the hard way, huh?
  • [if the protagonist previously tried sparing Sans]
    • woah, you look REALLY pissed off...
    • heheheh...
    • did i getcha?
    • well, if you came back anyway...
    • i guess that means we never really WERE friends, huh?
    • heh.
    • don't tell that to the other sans-es, ok?
• [Attack #15]
  • sounds strange, but before all this i was secretly hoping we could be friends.
  • i always thought the anomaly was doing this cause they were unhappy.
  • and when they got what they wanted, they would stop all this.
• [Attack #16]
  • and maybe all they needed was... i dunno.
  • some good food, some bad laughs, some nice friends.
• [Attack #17]
  • but that's ridiculous, right?
  • yeah, you're the type of person who won't EVER be happy.
• [Attack #18]
  • you'll keep consuming timelines over and over, until...
  • well.
  • hey.
  • take it from me, kid.
  • someday...
  • you gotta learn when to QUIT.
• [Attack #19] and that day's TODAY.
• [Attack #20]
  • cause... y'see..
  • all this fighting is really tiring me out.
• [Attack #21]
  • and if you keep pushing me...
  • then i'll be forced to use my special attack.
• [Attack #22]
  • yeah, my special attack. sound familiar?
  • well, get ready. cause after the next move, i'm going to use it.
  • so, if you don't wanna see it, now would be a good time to die.
• [Attack #23]
  • well, here goes nothing...
  • are you ready?
  • survive THIS, and i'll show you my special attack!
• [After final attack]
  • huff... puff...
  • all right. that's it.
  • it's time for my special attack.
  • are you ready?
  • here goes nothing.
  • yep.
  • that's right.
  • it's literally nothing.
  • and it's not gonna be anything, either.
  • heh heh heh... ya get it?
  • i know i can't beat you.
  • one of your turns...
  • you're just gonna kill me.
  • so, uh.
  • i've decided...
  • it's not gonna BE your turn. ever.
  • i'm just gonna keep having MY turn until you give up.
  • even if it means we have to stand here until the end of time.
  • capiche?
  • [Pause #1]
  • you'll get bored here.
  • if you haven't gotten bored already, i mean.
  • and then, you'll finally quit.
  • [Pause #2]
  • i know your type.
  • you're, uh, very determined, aren't you?
  • you'll never give up, even if there's, uh...
  • absolutely NO benefit to persevering whatsoever.
  • if i can make that clear.
  • no matter what, you'll just keep going.
  • not out of any desire for good or evil...
  • but just because you think you can.
  • and because you "can"...
  • ... you "have to."
  • [Pause #3]
  • but now, you've reached the end.
  • there is nothing left for you now.
  • so, uh, in my personal opinion...
  • the most "determined" thing you can do here?
  • is to, uh, completely give up.
  • and... (yawn) do literally anything else.
• [Attack #24] heh, didja really think you would be able to-
• [Attack #25 (automatic)]
  • ...
  • ...
  • ...
  • so...
  • guess that's it, huh?
  • ...
  • just...
  • don't say i didn't warn you.
  • welp.
  • i'm going to grillby's.
  • papyrus, do you want anything?

Flavor text

Any phase

• The easiest enemy. Can only deal 1 damage. [Check]
  • Can't keep dodging forever. Keep attacking. [Check after attacking at least once]
• You felt your sins crawling on your back. [Neutral, 0-10 KR]
• You felt your sins weighing on your neck. [Neutral, 10-20 KR]
• KARMA coursing through your veins. [Neutral, 20-30 KR]
• Doomed to death of KARMA! [Neutral, 30-40 KR, difficult to trigger due to KR drain rate]
• Skipped ahead. [Neutral; unused]

1st phase

• You feel like you're going to have a bad time. [Encounter]
• Just keep attacking. [Neutral]
• Sans's movements grow a little wearier. [After attacking four times]
• Sans's movements seem to be slower. [After attacking nine times]
• Sans is sparing you. [When Sans pretends to spare the protagonist]

2nd phase

• Felt like a turning point. [Neutral]
• The REAL battle finally begins. [Neutral]
• Reading this doesn't seem like the best use of time. [Neutral]
• Sans is starting to look really tired. [Neutral]
• Sans is preparing something. [Neutral, when he talks about his special attack]
• Sans is getting ready to use his special attack. [Neutral, when he talks about his special attack again]

Trivia

The Gaster Blaster's firing animation.

• The firing sound of Sans's Gaster Blasters consists of two layered sounds used by Asriel. First, the text sound when "ASRIEL DREEMURR" displays at the beginning of his battle (mus_sfx_a_gigatalk), and second, a beam sound used by Asriel's Chaos Buster and final attack (mus_sfx_rainbowbeam_1). The sound effects are pitched up, sped up, layered, and slightly offset from one another to make the Blaster's firing sound.
• Sans is the only monster to not have his health bar visible at all.
• When Sans first talks about his special attack, he asks the player if it sounds familiar. This is referencing Papyrus's special attack.
• Sans's dialogue before his first attack parallels Asgore's dialogue when the protagonist confronts him in the Throne Room on the Neutral Route. as they both use the quote "Birds are singing, flowers are blooming..."
• Sans and Papyrus's bones have different sprites; Sans has more rounded attacks, while Papyrus's are flatter on the top and bottom.
• The last two attacks on Sans, including the one that connects, always use the animation from the Real Knife, regardless of the weapon that is currently equipped. The same goes for the automatic attacks on Asgore, and all attacks against Flowey/Omega Flowey.
• If the game is closed during the battle, Sans counts this as a death when making his next comment before battling the protagonist again.

Version history

Version tag	Changes
v1.001	Fixed dialogue prior to Sans's first attack after the third death. Sans now always says "ready?" followed by "here we go."
v1.05	Fixed a bug in which several lines of Sans's pre-fight dialogue cut off early.