Memes/Undertale - TV Tropes

"Papyrus, what's your favourite food?" Alphys: i spend all my time browsing memes now. it's my element

Given its wacky sense of humor and immense popularity around the Internet, it only makes sense that Undertale has spawned a large amount of memes.

For memes related to Deltarune, see here.

Please add entries in the following format:

• The meme. [[labelnote:Explanation]]The explanation behind the meme.[[/labelnote]] ExplanationLike this.
  • Further mutations and successor memes, if any.

SPOILERS ARE UNMARKED, READ WITH CAUTION. open/close all folders

Sans and "Megalovania" Sans and his battle song are full of memes, to say the least.

• Basically anything said by Sans during a Genocide Run:
  • "Do you wanna have a bad time?" / "You're gonna have a bad time." Explanation (Spoilers)A line spoken by Sans before his boss fight / near the end of Snowdin, respectively, on a Genocide route, foreshadowing that he's going to give it his all to stop you if you continue down this path. Fans have latched onto it, using "having a bad time" as a euphemism for the extremely tough Sans fight and the Genocide runs in general, and it's often quoted out of context if something can be connected to those things.
  • A further application of the above is altering the phrase, accompanied by a poor MS Paint drawing of Sans. The most popular variation is "Sanesss", which originates from Underpants. Many people have called Sanesss the Undertale version of Mokey.
  • "geeettttttt dunked on!!!!" Explanation (Spoilers)A line Sans trolls you with on the game over screen if you spare him. Used to describe any sort of Curb-Stomp Battle, including the Sans fight, and has also been connected to Undyne using Alphys as a basketball during the latter's date sequence in a Pacifist run.
  • "on days like these, kids like you..." Explanation (Spoilers)Sans' brief speech before his boss battle has become very famous, and a defining part of the Sans fight. Often used out-of-context with the last part being cut out; even Toby himself has done this. It should be noted, though, that Asgore usually also says "Birds are singing, flowers are blooming", so it's possible that Sans took that quote and twisted it for the occasion.
    • "flowers are singing, birds are blooming. ...fuck." ExplanationA popular joke is of Sans flubbing his Pre-Asskicking One-Liner.
  • "hey there buddy chum pal friend buddy pal chum bud friend fella bruther amigo pal buddy friend chummy chum chum pal i don't mean to be rude my friend pal home slice bread slice dawg but i gotta warn ya if u take one more diddly darn step right there im going to have to diddly darn snap ur neck and wowza wouldn't that be a crummy juncture, huh? do you want that? do you wish upon yourself to come into physical experience with a crummy juncture? because friend buddy chum friend chum pally pal chum friend if you keep this up well then gosh diddly darn i just might have to get not so friendly with u my friendly friend friend pal friend buddy chum pally friend chum buddy" Explanation (Spoilers)A bastardization of Sans' speech to you before his boss fight in the Genocide route, which quickly became popular to quote among fans thanks to its comedically wordy language.
  • "You felt your sins crawling on your back." ExplanationA line reflecting how much trouble you're in against Sans. Fans have taken it and use it as guilt admittance, like "I felt my sins crawling on my back" or "Do you feel your sins crawling on your back?"
  • Taking an enormous amount of damage/having 1 HP and dying in one hit, usually from something innocuous. Explanation (Spoilers)Sans is "the weakest enemy," with all his stats set to 1, and — being the last enemy you fight on a Genocide run — takes more damage than anyone else when you finally hit him. Fans have made comedy out of this by claiming that Sans will die from stubbing his toe or a Bitch Slap.
• Farmer Sans/オイラショック (Oira Shock) ExplanationThe Japanese localization introduced in the trailer for the PS4 port had Sans referring to himself with the pronoun オイラ (oira). However, oira is commonly associated with people from a rural background, hence the Japanese fandom responded with fanart depicting Sans in such a manner.
• "you dirty brother killer." ExplanationSaid by Sans if the player kills Papyrus on a Neutral run. And to many a player, anyone who actually goes through with killing Papyrus is very much deserving of being labelled as such.
• PTA Sans ExplanationAn AU (alternate universe) where Sans becomes Frisk's awesome parental figure and becomes involved in Frisk's school, often butting heads with two antagonistic parents named Linda and Helen. Hilarity Ensues. seems to be working its way around Tumblr.
• AU where Sans is a troper! ExplanationUndertale has a very large amount of fan-made alternate universes, many of which are heavily Sans-centric or built around a certain theme, so a common response to fan-art or fan-made content is to describe a joke AU with the context of said fan-art.
• Sans is Ness. ExplanationA theory focused on in Game Theory's video on Undertale. Due to the infamous reputation of Game Theory on parts of the web, combined with the fact that Toby himself publicly denied this theory, this frequently gets brought up by fans when talking about outlandish fan theories.
  • "Sans is already in Super Smash Bros.." ExplanationThe reveal of Super Smash Bros. Ultimate and a Switch port of Undertale on the same day gave rise to a slew of posts that, jokingly or otherwise, suggested an Undertale character for Smash — Sans naturally being one of the most frequently seen. Many people joked that, since Game Theory claimed that Sans is apparently Ness, he's actually been there right from the start.
• "SANS IS ACTUALLY IN SMASH" ExplanationOn September 4th, 2019, Smash fans were in for a surprise when, shortly after a Nintendo Direct, it was revealed by Sakurai that Sans was actually coming to the game as a Mii Gunner costume, along with a remix of Megalovania from Toby Fox himself. While that didn't exactly make him a playable character, he got far closer than anyone thought he would get, leading to a fresh surge of "Sans for Smash" memes.
  • Sans isn't actually in Smash.ExplanationSince Sans is only a costume, his status as The Slacker led to jokes that he was too lazy to actually show up, and instead just sent them his outfit and a mask. Or alternatively, it's the player character who's wearing the costume. An interview with Sans and Papyrus mentions this.
• Steven After Not Surviving ExplanationSomeone (LouLouVZ, creator of Spaicy) posted what was a parody of the more outlandish theories, suggesting that Sans is Steven Universe after dying of cancer. Naturally, this sparked a further escalation of increasingly absurd fan "theories" trying to one-up each other in terms of sheer implausibility, leading up to acronyms like "Secretly Actually Ness Skeleton" (see above) or "Shrek After Nuclear Strike." This meme would later on be referenced in Deltarune's "$pamton's $weepstakes" event where one of the items in the website for the event (a jar of white sand with a pink ball and a yellow ball) was referred to as "Spamton After Not Surviving".
• so cool! so cool! so cool! so cool! so cool! ExplanationThis seems to have been accepted among the fans as Sans' default response to anything and everything he finds on the internet.
  • SANS, WHAT ARE YOU DOING? SANS! SANS! SHUT THE FUCK UP, SANS!ExplanationPapyrus' response to the above.
• Sans Undertale ExplanationSans' popularity eventually got so intense and overbearing that his fandom caved in on itself, leading to this meme being used to poke fun at him and his remaining fans. It began as just a bastardization of his name, and was later accompanied by a picture of a poorly drawn Sans or another massively popular character from another fandom (most commonly Nagito Komaeda from Danganronpa who received a similar treatment) badly photoshopped over a picture of the Judgement Hall at the end of the game. Later on, this mutated into anytime Sans, the song Megalovania, or both appear out of nowhere in videos or other games. This meme has since reached a level of ubiquity to the point where pretty much any fictional character you can think of has been referred to as if their last name was the name of the work (written as one compound word if necessary).
• First Four Notes of Megalovania ExplanationThe above meme mutated into a new meme due to the frequent use of Megalovania in memes. The song was so insanely popular even before this that it is now immediately recognizable with just the first four notes (or even less), which has become a meme in and of itself. Some people who are not Undertale fans, and even some that are, find the song overdosed and overplayed, so when the first four notes of it appear out of nowhere it's meant to be a jab at people who are irritated by it.
  • EarthBound SoundFont > Overdriven Guitar ExplanationThe specific sound used for the ostinato used in Megalovania is a sample originally recorded by Shigeru Miyamoto on his guitar for the finale of EarthBound, which in the first part of the final boss sports a fairly heavy metal-style boss theme. Being instantly recognisable nowadays due to Undertale's popularity, the extremely compressed sample has become somewhat of an inside joke among those knowledgeable in music production.
• Sans Fangirls. ExplanationAs mentioned above, Sans's popularity was so intense his fandom collapsed in on itself; this is partially attributed to some younger fans of the game liking him so much that they proceeded to create characters to ship him with, usually poorly-drawn girls who go Yandere at the drop of a hat and threaten to (or in some cases outright) brutally murder their "rivals". Nowadays, you have a higher chance of seeing parodies of these fangirls than seeing any genuine fans.
• Canon Sans vs. Fanon Sans. ExplanationSans' implied depression is a common focus in fan works, but a great deal of them completely miss the mark on how it manifests. In particular, he's frequently portrayed as being extremely emotional and breaking into tears at the drop of a hat, while his canon self portrays it as a complete lack of emotion and motivation. Similar to the "Sans Fangirls" above, fans have parodied this, making humorous comparisons between the two, or portraying them as separate characters altogether. The "canon vs. fanon" comparisons are also applied to other oft-mischaracterized characters (such as Chara and Papyrus), but Sans is by far the most common.
• This image of Monika T-Posing over Sans. ExplanationA fan art made by sansurichin, the pose is used to depict dominance from one side (Monika) and the other side cowering in fear (Sans). As DDLC came to be another genre-subverting game of the later 2010's, the similarly meta-aware Monika came to become as memetic as her peer Sans. Monika's full-blown Breaking the Fourth Wall habits made her incredibly Genre Savvy even in comparison to Sans, thus the joke being that a random high school girl was able to intimidate a Memetic Badass into submission. Label edits of this particular image became very, very popular soon after.
• "Fingers in his ass Sunday". ExplanationA crude MikuMikuDance video of Sans and Nagito Komaeda dancing in the Last Corridor, set to a remix of "ASGORE" by YouTuber BotanicSage that centers around an infamous Amber Rose tweet about Kanye West's sex life. The absurdity of the video and its surprising appropriateness to both Sans and Nagito's personalities made it quickly catch on among Undertale fans, and since then it became a tradition to repost it every Sunday on Tumblr.
  • "The last legal Fingers in his ass Sunday". ExplanationAs December 16th, 2018 was the Sunday before Tumblr enacted its ban on Not Safe for Work content, users of the site have dubbed that day as such, with many artists drawing works of Sans and Nagito Komaeda sharing incredibly heartfelt goodbyes as they face their (theoretical) end. Many users have expressed their disbelief at themselves getting emotional over the meme itself, while others argued there’s not much point to the date name considering people are still going to make content of the meme after the ban’s enactment.
• Sans Default Dancing.ExplanationGiven that both Sans and Fortnite dances are incredibly popular in ironic memes, a combination of the two was pretty much inevitable. This ended up becoming canon thanks to the 5th Anniversary Alarm Clock app dialogue.
• "Maybe it's the way you're dressed?" ExplanationIn 2019, the Soundcloud account "UNDERTALE OST: Recreated" did some detective work, and found out that Sans's "voice" snippet was trimmed from Patrick Star saying "maybe it's the way you're dressed" in the SpongeBob SquarePants episode "Something Smells". SpongeBob being as ripe for memes as it is, the jokes wrote themselves.
• Sans with a Gaster Blaster Arm Cannon ExplanationAfter being made into a Mii Costume in Super Smash Bros. Ultimate, he got classified as a "Mii Gunner", meaning that he has to carry an Arm Cannon. The design team chose a Gaster Blaster, and many memes started portraying Sans having said Arm Cannon attached to himself in the game, with the other characters having appropriate reactions to Sans constantly holding a weapon.
  • "Nobody cared who I was until I put on the mask." ExplanationA joke playing on how the Mii Gunner was seen as a generally unremarkable character before experiencing a drastic increase in popularity after Sans became a possible alternate costume for them.
• Sans merely existing has become a meme itself. This video states that every single bit of Sans has become a meme in its own way, and this led to things like Sans being a Mii Fighter costume in Super Smash Bros. Ultimate, as Kenny Omega's costume in All Elite Wrestling's Halloween promo, and appearing on Jack Black's t-shirt◊.
• Sans Console.ExplanationThe PlayStation 5's designs got fans comparing it to Sans' design and colors, particularly the DualSense controller design. The fact that Undertale as a PS4 game that can be backwards-compatible with PS5 doesn't help.
  • DualSans controller.ExplanationThe PS5's DualSense controller has its name struck with a Punny Name by slapping Sans' name into it. Even the edits of the controller have Sans' face slapped on it.
• Megalovania but ExplanationA sudden wave of Megalovania mixes flooded Youtube soon after - Yukiko - uploaded a video called "Megalovania but beats 2 and 4 are swapped". The end result? Somehow, it still ended up being a good track. This caused a number of others to try their hand at mixing the song in its vein, eventually evolving to the rest of the soundtrack as a whole.
  • Making Megalovania sound bad / You cannot make Megalovania sound bad ExplanationThe "goal" of the people who mix up Megalovania, as said by the comments section, is to make Megalovania sound bad. These mixed up versions always sound good, so people have joked that you cannot make Megalovania sound bad no matter how hard you try.
• X but it's Megalovania. ExplanationRemixing songs with Megalovania's soundfont. The same works with Bonetrousle.
• Perfectly timing Megalovania's beat drop at 12 AM on New Year's day. Explanation Videos of people doing exactly that. See for yourself.
• "call it knochen könig and have it be for storyshift sans" Explanation (spoilers)On SoundCloud, some fans make remixes of the game's music where they combine certain characters' leitmotifs with other characters' leitmotifs for fanmade AUs. There's a bit of a debate over whether "Megalovania" is Sans' leitmotif, Genocide Chara's leitmotif, or the Anomaly's leitmotif. And fans who think it's Chara's theme would make remixes of "Bergentrückung" and "Asgore" and apply "Megalovania" to it, and fans who think it's Sans' theme would harass the uploaders telling them to rename it to "Knochen König", which is German for "Bone King". And people eventually just started jokingly saying it on remixes of completely different songs.
• Sans GamingExplanationA YouTube channel where every single video name and description are nothing more than "Sans Gaming". The uploads solely consist of weird and bizarre memes, which often have very little to do with Sans and absolutely nothing to do with gaming. This likely exists as a way to mock a popular belief within the Undertale fanbase that Sans would make a funny Let's Play YouTuber if he existed in real life.
• Garfield and SansExplanationThanks to Toby Fox having a well-documented history of referencing Garfield in his pre-Undertale output, fans of both the game and the comic strip took to making fan content associating Sans with Garfield, himself a fellow Fountain of Memes, be it through depicting the pair interacting or depicting one taking the role of the other. The fact that Toby himself uses a Garfield/Sans fusion as his Minecraft skin only amplified the jokes connecting the two characters.
• The PoopshittersExplanation An image of a group of realistic Sans with the aforementioned title became popular in 2021, often portrayed as a music band.
• #SANSSWEEP ExplanationIn September 2022, the Twitter account Tumblr Sexyman OTD hosted a "semiannual sexyman showdown" poll to crown the ultimate Tumblr Sexyman. In the final round, Sans went against Arataka Reigen. With both characters' Memetic Badass status and being very popular sexymen, the poll inspired a lot of bickering, memes, and fanart of Sans and Reigen fighting (or making out). Eventually, Sans won by just 0.1 percent out of over 244 thousand voters, and even Toby Fox himself had something to say about it.
  • The Sans Sweep was so strong it killed the Queen. Explanation Queen Elizabeth II passed away less than a day after Sans won the Tumblr sexyman poll. Many people have commented on the unusual coincidence of how the two contrasting events happened so close in time, with some even joking that the competition is what killed her.
• Hey kid, do you want a weiner in your mouth? ExplanationA fanart of Sans holding a hotdog accompanied by a voiceover of him asking the viewer if they want it in their mouth became a popular Bait-and-Switch. The original artist of the fanart even redrew it in honor of the meme.
• whoa hey pal lets back it up a bitExplanationA reaction image with Sans in a Spooky Dance pose where he looks like he's holding his hands out between him and something disturbing or surprising.
• "human... i remember you're genocides." ExplanationAn edit of Sans's first encounter where he says this line, parodying low-quality fan content and creepypastas involving the Genocide route. This spawned numerous similar edits of both this game and Deltarune, including two variations of the Sans edit corresponding to the other routes in the game.
• "why'd you jump?" Explanation In the game mod Undertale Red & Yellow, Sans can Troll the player on a Pacifist route if they agree to fight him, with him mimicking his Genocide fight until the first and only attack (which is bones on top of the battle box instead of the bottom). With a lot of people's muscle memory having them unnecessarily jump, many fans made edits of the scenario where Sans takes note of that.
• "well this stinks" *starts crying*/2024 fanon Sans vs. 2016 fanon SansExplanation (spoilers)On August 31st, 2024, a Twitter(X) user by the name of @Homdogger posted a drawing comparing how Sans reacts to Papyrus's death if the player kills him (mildly inconvenienced) to how the early days of the Undertale fandom portrayed it as (incredibly emotional). The drawing was ultimately criticized as mischaracterization fighting mischaracterization, as it downplayed how much Sans cared about Papyrus. Nearly a year later, the drawing went viral due to reignition of discussion of Sans's character as well as the fact that, when taken out of context, looks like Sans immediately started crying comically after responding in a deadpan tone, to the point that fans did their own spin on it by redrawing it or make their own version with different characters, Undertale or not. As of late, many voiceovers also involved Sans' crying being pitch shifted to emulate the opening of "Faded" by Alan Walker.
• Sans is now forklift certified. Explanation In the 10th anniversary stream on day 2, the goal for fighting Sans and having him actually attack was reached, and Sans ended up giving the audience a goofy battle where the loss condition was his non-damaging bones pushing the player off the screen. At the end, Sans uses a bulldozer to push the player out of the battle. Fans immediately latched onto this, noting that this meant Sans has a heavy machinery license, which meant he qualified for the "forklift certified" meme.

Specific characters Of course, other characters of the game are as popular and memey as Sans is.

Flowey/Asriel:

• "Friendliness Pellets". ExplanationFlowey attempts to trick the player at the beginning of the game by telling them to touch his deadly magic bullets, saying that they're actually "friendliness pellets" that monsters communicate with. It's Flowey's Establishing Character Moment, so they're often connected to him and "LOVE" in general.
• "In this world, it's kill or be killed". ExplanationOne of Flowey's first, most memorable, and also most frequently used phrases. Much like Sans' "do you wanna have a bad time?", this phrase is frequently altered and accompanied with a conksuck drawing of Flowey or paired with an image of a flower with a face.
  • It also spawned a lot of derivatives following the format "In this world, it's [X] or be [X]ed".
• Omega Everyone Explanation (spoilers)As the final boss of the Neutral route, Flowey gains a monstrous photorealistic form known as "Photoshop Flowey" or more commonly "Omega Flowey". It is common for fanartists to create similar Omega forms for other characters, such as Temmie◊, Papy◊rus◊, Aaron◊, Woshua◊, Burgerpants◊, Lesser Dog◊... and Donald Trump◊?
• ______ is now playing Undertale______ is now playing Undertale______ is now playing Undertale______ is now playing Undertale______ is now playing Undertale Explanation (spoilers)Photoshop Flowey is a very difficult boss in the Neutral Route. Upon losing to him, he will crash the game, forcing you to restart it, which pops a toast notification to your Steam friends.
• Big boner down the lane ExplanationA silly-sounding Dummied Out bit of text in the game's files. The phrase gained popularity after a video of a corrupted version of the game showed Flowey saying it right before his boss fight.
• But it refused. Explanation (spoilers)In Asriel Dreemurr's fight, dying will cause your SOUL to break apart, but it refuses to die and continues the fight. The text accompanying it, "But it refused.", has been used for strength and encouragement in the fandom, and is also used whenever something that someone doesn't want to happen occurs anyway, and vice versa.
• Wide Asriel Explanation (spoilers)When Asriel transforms into his final form, he briefly widens his body. This scene is often compared to the "Wide Presidents Walking" meme.
• Emo Asriel and his edgy OC Explanation (spoilers)Asriel is often portrayed in not-so-serious fanworks as an emo teen, and his final form (and less commonly, Photoshop Flowey) is often joked to be his OC that he created before he died, to the point that some treat it as Fanon. Became Hilarious in Hindsight when the artbook revealed that Toby Fox considered giving him "boyband hair".
  • Kids on the playground Explanation (spoilers)Due to this, it's common to compare the ending of the Pacifist Route to a playground fight where Asriel uses his Laser That Kills Anything And Everything but Frisk blocks it with their Shield That Specifically Blocks The Laser That Kills Anything And Everything.
• Photoshop Flowey: NO!! NO!!!!! YOU CAN'T DO THAT!!! YOU'RE SUPPOSED TO OBEY ME!! The seven human souls: ExplanationIt's common to respond to pictures of seven things in different colors by quoting Photoshop Flowey's dialogue when he is defeated, followed by "The seven human souls/[things in the picture]:". It's also used as a general snowclone for groups rebelling against their masters.

• Hideo Kojima: I will help you Explanation A screenshot of the Photoshop Flowey boss fight, in which you are mocked for wanting to call out your mom or dad for help, with a Steam message from the Metal Gear Solid creator, insinuating that Kojima himself would interfere with the game to help you.

Toriel:

• Goat Mom is Best Mom. ExplanationAlthough a clear example of My Beloved Smother, she really does want only the best for the protagonist. Today, there's tons of art showing her being genuinely motherly to either the protagonist, or other characters.
• Don't sexualize goat mom. ExplanationShortly after the demo's release, Toriel became a prominent source of Rule 34 primarily from the Furry Fandom. This is a common response to said smut, or a message not to make it.
• "if you were the toriel cosplayer who gave me a blowjob at dragoncon, PLEASE inbox me. i think you took my wallet. it looks like an NES" ExplanationAn infamous Tumblr post. Nothing more can be said, aside from the fact that it's likely fake (DragonCon occurred before the game's release, but fandom around Toriel had already formed after the demo's release).
• Toriel vaping. ExplanationMore specifically, pictures of a person in a Toriel fursuit vaping that caught on due to how much it contrasts with Toriel's personality.
• tuTORIEL ExplanationA portmanteau of tutorial and Toriel. This is usually inserted into Undertale tutorial videos as a comment. Ended up reaching Ascended Meme status in Deltarune, where Chapter 2 sees Kris' prison cell in Queen's mansion decorated with items based on their search results, including two piano-playing Toriel holograms because they searched "video game piano tutoriel".
• Homophobic Toriel. Explanation (spoilers)Some players have noticed that Gerson talks about how Toriel and Asgore used to display affection in public when they were married, while Toriel stops Undyne and Alphys from kissing in front of Frisk in the True Pacifist Route. This, along with Deltarune implying that she's religious, has caused fans to jokingly theorize that Toriel is homophobic, and that the reason she and Asgore are divorced in Deltarune is because she disapproved of Asgore's feelings for Rudy.
• my child you are breaking my heart ExplanationIn the release trailer, there's a scene where a CGI Toriel crashes into blocks with the above text, with the text "Probably not actual game footage?" under it. Needless to say, this scene isn't actually in the game. This scene is probably the trailer's most well-known scene due to its absurdity, and the CGI Toriel has since also appeared in the Nintendo Switch trailer and the 6th anniversary livestream.
• Toriel MittExplanationFangamer's Undertale Kitchen collection included an oven mitt designed to resemble Toriel's head. Both in the video and the Fall 2024 UTDR Newsletter, the Toriel Mitt would end up doing various antics, like brandishing a knife only to use it to cut the pie. This made the Toriel Mitt beloved among fans

Papyrus:

• "That's the trash can. Feel free to visit it any time." ExplanationPapyrus says this during the date if you examine his trash cans. Fans have re-appropriated it for a variety of purposes, the most popular being the "Sans dies first and Papyrus becomes a vengeful badass" Fanon as his variant of the "get dunked on" quote above.
• "The internet! I'm quite popular there!" ExplanationIn-universe, this is just Papyrus being a comically oblivious Small Name, Big Ego as usual. He's twelve away from a double digit follower count; think about that for a second. How did Papyrus get -2 followers? Out-of-universe, he's possibly second only to his brother in overall popularity among the Undertale cast.
• "I didn't cry! I just… caught something in my eye." "What did you catch?" "TEARS!" ExplanationAn exchange between Papyrus and Sans that's used when referring to the sadder moments of the game.
• Papyrus and spaghetti. It's become a symbol for him.
• "Oh, no! You're meeting all my standards!" ExplanationIf you flirt with Papyrus at the beginning of the battle, he asks what your redeeming qualities are, warning you that he has very high standards. Regardless of what you choose (and your choice is between "I can make spaghetti" and "I have zero redeeming qualities") he reacts with this line, which is used as a form of Self-Deprecation on the fandom's part whenever they find someone sharing their interests.
• "You're blue now. That's my attack!" ExplanationPapyrus' famous "blue attack" turns your SOUL blue. Quite a bit of fanart has been made of this moment. It has also been used in response to images that are blue, especially if the image wasn't originally that color.
• "Sans! Stop plaguing my life with X!" ExplanationA snowclone based on one of Papyrus's lines; the original line was "incidental music." When Papyrus discovers that his bone collection has been stolen by the Annoying Dog, Sans pops his head out of his room just to play Losing Horns for the occasion. Papyrus responds with this line.
• Referring to concept art Papyrus◊ with various bastardized names such as the Alright Papyrus, Papaya, Paperpenis, or Popeye.
• Papyrus no longer believes in you / "I'm going to have LOTS OF FUN!" Explanation (spoilers)Two quotes mentioned within videos of Genocide Papyrus, the first connecting with his Genocide theme, DISBELIEF, and the comic video, Papyrus no longer believes in you, while the other comes from the comic video itself.
• Nobody kills Papyrus / The hardest boss of Genocide run. ExplanationPapyrus has developed a reputation for making Genocide runs very difficult — not because he's hard, far from it (on Genocide, he immediately spares you and refuses to attack), but because players simply cannot bring themselves to harm Papyrus.
• Reading Papyrus' dialogue in Skeletor's voice is practically a requirement now.
• "Papyrus, what's your favourite food?" ExplanationOn the one-year anniversary of Undertale’s release, Toby Fox made a Q&A blog where he proceeded to answer ten user-submitted questions. The submission page used an example of "Papyrus, what's your favourite food?" At least ten users submitted that as their questions, and Toby ended up only answering that question.
• RED X ARE IMPASSABLE! YOU CANNOT WALK ON THEM! YELLOW X ARE ELECTRIC! THEY WILL ELECTROCUTE YOU! etc. ExplanationWhenever Undertale fans see a picture of a bunch of colored squares, or pretty much anything that comes in a lot of colors, it's pretty common to see comments quoting Papyrus' explanation for the tile puzzle's rules.
• Let Papyrus Say Fuck Day ExplanationJune 16th has been declared Let Papyrus Say Fuck day, a day where the Tumblr side of the fandom makes posts involving Papyrus doing "adult" things such as swearing or committing crimes, to combat the frequent infantilism done to him by the fandom.
• Papyrus is Uncle Aaron.Explanation A Twitter user noticed that Uncle Aaron and Papyrus have a similar head shape. This has led to memes and edits about them secretly being the same person, in a similar vein as the "Steven After Not Surviving" meme about Sans, often with acronyms like "Prowler After Perishing".
• WHAT IS A SKELETON'S FAVORITE SNACK?!ExplanationYoutuber and voice actor Tom Schalk made a video of himself messing with a skeleton puppet, trying to tell a joke to a friend and becoming irationally angry when he can't guess the answer. Due to the loud gravelly voice Tom used, people associated the audio with Papyrus, making animations of Papyrus trying (and failing) to tell a joke and becoming comically angry in the process.
• Realistic Papyrus images ExplanationA popular meme among artists is for Sans to tell a pun, and the image turning to Papyrus suddenly having an 100% realistic human skull to convey his Lame Pun Reaction. Others like to combine the realistic human skull with "Let Papyrus Say Fuck" Day.
• Omni-Man vs. PapyrusExplanationA fan video by XCRISX Gamer featuring Omni-Man fighting against SCP-096. The scene in the sun featuring a skeletal SCP-096 finishing Omni-Man off resulted in memes referring to the former as Papyrus while Bonetrousle played in the background, even jokingly mutated to Papyrus if his battle sprite moved.

Undyne:

• "Undyne suplexes a huge boulder, just because she can." ExplanationOne of the descriptions in the dialog box during the fight with Undyne reflecting her Hot Blooded-ness. It's become a snowclone, with "huge boulder" being replaced with something else.
  • "Undyne suplexes herself, just to prove that nothing is impossible." ExplanationAnother description from her fight, popular due to how absurd it is, and the obvious question of how it's even possible.
• "ANIME'S REAL, RIGHT?!?!"
  • ♥ Anime is real
  • Anime is not real. Explanation (spoilers)At the end of the "date" with Alphys, Undyne has a brief crisis when she's faced with the possibility that "human history" is not actually truthful, and asks you the truth in her panic. It's given as much attention as some far more important choices in the game, and the sheer ridiculousness has led to this question being tossed around as Serious Business. Also, anything relating to Undyne the Undying will be met with at least one person saying that, yes, anime is real.
• Her cooking methods. Mostly because it connects with Papyrus and his spaghetti.
• "WELL??? Are you CHERISHING??? CHERISH HARDER!!!" ExplanationIf you befriended Undyne and call her in the room with the bird that flies you over a disproportionately small gap, she tells you to cherish the bird. Calling her again causes her to say this line. Fans of course adapted it to cherishing all kinds of things.
• Fish Vriska ExplanationUndyne bears many resemblances to Vriska Serket of Homestuck, both in appearance and personality.
• Undying ZUNpets / Undyne the unused Touhou Boss. Explanation In a crossover meme with the Touhou Project, a lot of people have noticed how Touhou's memetic "ZUNpets" use the same sample ("Romantic Tp. from the Roland SD-90") as the trumpets used in Undyne's "Battle Against A True Hero" boss theme. "Battle Against a True Hero" also uses a very similar song structure to many lategame Touhou boss themes. Not only that, but Undyne is one of the definitive difficulty spikes in Undertale's Genocide run, so people commonly joke that Undyne channeled her inner Touhou to make the Bullet Hell segments of her bossfight much harder. As Toby is a known fan of the Touhou series, these references are likely intentional.
• * Seven. ExplanationUndyne's first spoken line in the game has her stating that seven human SOULs are needed in order to break the barrier. The first part of this has her simply uttering "Seven.", which many have divorced from the rest of the line for the sake of jokes, mainly revolving around asking Undyne questions where seven is the answer (I.E.: "Hey, Undyne! What number was six afraid of?"),

Mettaton

• Mettaton going "Awooga." ExplanationA joke he makes if you compliment his voice during his boss battle — he has the voice of a siren, see.
• Mettaton's flamboyant posing is a meme in and of itself, often being compared to JoJo's Bizarre Adventure or David Bowie.
• "Would you smooch a ghost?" Explanation (spoilers)Partway through Mettaton's quiz, he asks the player this question, and rigs it so that it can't be answered with anything but "Heck Yes", because Mettaton is a ghost and is inflating his ego as usual. Fans use it for both Mettaton himself (mainly his attractive EX form), as well as resident adorable ghost Napstablook.
  • "Would you smooch a goat?" note An offshoot of the above meme, based around the Dreemurrs.
• Mettaton's legs. Explanation (spoilers)It's become popular to add his EX form's legs onto other characters from the game (mainly Sans, for the comedy inherent in his being one of the shortest characters). Possibly in response to his line, "Who needs arms, with legs like these?" if you remove his arms during the battle.
  • leg so hot, hot hot leg, leg so hot, you fry an egg. ExplanationThis predates Undertale by at least a few years, but it seems to have become the standard response to anything that involves Mettaton's legs.
• Mettaton NEO is infamous for being a literal Zero-Effort Boss despite looking awesome and having a badass buildup. Many YouTube videos and Vines exist dedicated to mocking how ridiculously easy the battle is. Or, alternatively, to try to give him an opportunity to shine and to be a badass.
  • Some have joked that NEO stands for Non-Effective Obstacle. However, this joke is dead as of Chapter 2 of Deltarune, whose secret boss, Spamton NEO, not only is the strongest boss in the chapter, but he even turns Nigh-Invulnerable in the Weird Route.
• OOHH YEEES~ ExplanationMettaton says this in a very sexual manner upon transforming into his EX form. It's one of the very rare quotes in the game not to use Voice Grunting. Because of these reasons, it's become a popular sound effect. His "YEAH," the sound he makes when you hit him during his boss battle, also qualifies as a meme, although it's less common.
• Similar to Papyrus, anyone familiar with Markiplier tends to use his voice for Mettaton.
  • Even Markiplier himself decided the character sounded like him... leaving him to do an impression of himself for all Mettaton's dialogue.
• Everybody gangsta until the calculator turns into David Bowie. ExplanationA lot of jokes are made about the contrast between Mettaton's initial simple box form and his fabulous humanoid EX form.

Asgore

• Asgore "You Must Be This Tall To Live" Dreemurr explanationDue to being partially, if not completely, responsible for the deaths of (what were likely) 6 children, the fandom loves to create nicknames like these◊ for him.
• ASGORE YOU USELESS FUCK ExplanationProbably due to this, a common joke is that the barrier isn't that big of a deal like Asgore makes it out to be, and that there were probably several workarounds that he could've used to free everyone instead of waiting for humans to drop in (such as digging under the barrier).
• Asgore Did Nothing Wrong ExplanationAsgore's fans have taken it upon themselves to create a counter-meme to the above.
• Asgore "Epic Divorce Man" Dreemurr ExplanationThe result of a tumblr combining tweets from the infamous "dril" account with pictures from Undertale (this one in particular). Has probably been strengthened with the release of Deltarune, as it seems that Toriel and Asgore's wholesome marriage really does tend to end with the two of them on bad terms in every universe.
• NO MERCY/Asgore Fight In A Nutshell ExplanationIt's very common to edit videos involving someone smashing an object into bits into parodies of Asgore destroying the Mercy button before his fight, as shown here.
• Asgore named X. ExplanationAsgore is well known for his poor naming skills, to the point that things with overly specific or bluntly descriptive names are often joked to have been named by him.
• Burgertrucking ExplanationA frequent misspelling of Asgore's pre-battle theme, which led to some fanart of Asgore running a burger truck.
• Dentist Asgore. ExplanationBefore the battle with Asgore, he tells you to "think of it like a visit to the dentist". This has led to fanart and memes of Asgore as an actual dentist, often replacing his trident with a giant toothbrush. Alternatively, since he compares a fight to the death to a dentist visit, there's some jokes about him being scared of dentists, too.

The Fallen Human/Chara:

• 201X/The first human has fallen. ExplanationThis meme began circulating around New Year's of 2019. Since the year Chara fell down was "201X" according to the game's intro, this means that 2019 is the last time Undertale could have taken place in. With the revelation that there is an actual Mt. Ebbot in Spain, people began speculating that Chara had already fallen down the mountain, and that the events of the game will take place in the future. Even Toby Fox got in on this meme.
• I am [insert something silly] Explanation (spoilers)When you meet Chara at the end of a Genocide run, they introduce themself: "I am [player's name]". Fans jumped on the opportunity to humiliate the detested child by inputting stupid things at the start of the game and watching Chara◊ insult themself◊. (The latter screenshot is obviously edited, but it's still possible to have Chara say that, minus the rainbow effect. Also note that the fallen child's name cannot exceed six characters without editing the game. However, even with these limitations, some still make jokes with the name.)
  • You're not actually [something stupid], are you? SpoilersLikewise, Asriel's line from the Pacifist route gets abused as well.
• No chocolate. SpoilersA sentence pronounced (or thought) by Chara in red letters when looking in Asgore's fridge in a No Mercy run. Because of its silly and unexpected nature, especially when you think it is the character whose obsession is to kill everyone who says that, the Fallen Human's taste for chocolate has been flanderized to obsession on the Internet, making them a Draco in Leather Pants.
  • Chara hates white chocolate. SpoilersAmong chocolate-lovers, white chocolate is frequently compared unfavorably to milk and dark chocolate thanks to it consisting mainly of cocoa butter with no actual cocoa solids. Consequently, several members of the fandom have decided that the chocolate-loving Chara holds similar disdain for white chocolate. An example here.
• Discussions about Chara's morality are a meme by themselves. While some still want to argue peacefully (or simply refuse to take one side or another), two radically opposite "squads" formed to convince every other fan with their ideas:
  • Chara Protection Squad Explanation (spoilers) Because of the longstanding debate over whether Chara/the Fallen Human is actually evil or not, those who believe they are good have labeled themselves the "Chara Protection Squad" (or "Chara Defense Squad"). This has crossed over to other works with other Character Protection Squads.
  • Chara Offense Squad Explanation (spoilers) In contrast with the above, those who believe Chara to be truly evil to some degree call themselves "Chara Offense Squad" in contrast with the ones above, accusing them of being too biased and ignoring important points of the story. They also ask themselves how much the Fallen Human really cared for the monsters and their adoptive family.
• Chara's name debates.ExplanationAmong the many aspects of Chara that are hotly debated, one of the sillier/more minor ones is how to pronounce their name. Fans are split between calling them "Car-a", "Care-a", and "Char-a", although one thing they all seem to agree on is that it should never be pronounced "Chair-a".
• Comparing (Genocide) Chara to Not Important.ExplanationThey both want to kill everyone, if for wildly different reasons. Also may have to do with how he proclaims "My genocide crusade begins here" in the teaser trailer for the game.
• You can't spell DETERMINATION without TERMINATION. Explanation Is sometimes used when players talk about the Genocide run. Most of the time it is pasted over a picture of Chara.
• Chara's flesh stripe.ExplanationDue to the limited color palette of Chara's sprite, the stripe on their shirt is the exact same color as their skin. This has led to all sorts of alternative interpretations of their appearance, from Chara wearing a crop top to their clothes being made of flesh.
• Christopher MoonExplanationA YouTube user with a Chara profile picture who comments under popular videos, mainly Undertale or Deltarune-related, and who’s often pointed out for "being everywhere", not unlike the character they use as a profile picture.
• Why would Chara make me do this?ExplanationIn the early days of the Undertale fandom, it was common for fans to portray Chara as the Big Bad of the Genocide Route, due to the implication that they possess Frisk's body over the course of the route. This sentiment later died down as the themes of the route were examined more closely, as it became seen as a way for Genocide players to absolve themselves of guilt for killing everyone. Nowadays, the "Chara is the killer" interpretation is a popular subject of parody, with fans blaming Chara for everything bad that they do, no matter how implausible.