YMMV / Undertale

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  • Abandon Shipping: After the Version 1.01 patch in January of 2016, modified content in the game added stronger implications that Sans is related to Gaster in some way, possibly as family. This has caused a lot of people to jump off the Sans/Gaster ship.
  • Accidental Innuendo:
    • If you call Papyrus at the snail farm he will mention that the snails are "just like his brother;" as they're "round, slow, and... always emitting slime?" He was most likely referring to the ketchup he drinks leaking out of his ribcage, but you really never know. It doesn't help that if you call him again he adds "Emitting slime... that's just what brothers do!", as if you just questioned him about it.
    • Not the dirty kind of innuendo, but Asgore is first encountered in his garden with his back to the player. He tells them that he's just finishing "watering [the] flowers", and his sprite shakes a couple of times before he turns around... Well, sorry if I walked in on you relieving yourself in the plants, Asgore.
    • In a similar vein, the fact that Burgerpants is at his calmest when smoking his Cigarette of Anxiety gives the impression that he's not smoking a normal cigarette.
      • The fact that his sclerae look slightly red when he's smoking doesn't help.
  • Alternate Aesop Interpretation:
    • Due to how surprisingly deep this game is and Toby Fox not going into detail about what things in the game mean, many folks have come up with other interpretations as to what the game means. Some feel that how Chara steals your soul at the end of a No Mercy run and how the only way to fix it is to delete your save file gives off the moral, "The only way to move forward is to burn your bridges."
    • People have also said the meaning is either the same or the complete opposite of The Stanley Parable — that the only meaningful choice you can make in a video game is to turn it off and walk away forever. Undertale puts huge emphasis on actions having consequences, but it also points out that it's not meant to have infinite replay value. It doesn't help that the message you receive at the end of the pacifist route rather explicitly aims towards the middle ground of these two — don't stop until you make it to the ending that's happiest for everybody, and then stop playing forever.
    • Some of the routes in the game, between pacifist and No Mercy, have a bit of a brush with Fantastic Aesop: "If you have the power to rewind time, you have no excuse not to do the very absolute best." The likelihood is this is meant to be taken as an elaborate, fictionalized way of saying Comes Great Responsibility.
    • Attempting a Pacifist run after successfully finishing a No Mercy run elevates this to Space Whale Aesop: "If you have the power to rewind time and you abuse it too much, an evil spirit will steal your soul and kill everyone you ever cared about."
      • Perhaps more likely, this could be interpreted as "Some mistakes are too terrible to ever be undone. Sometimes things can't be completely fixed."
  • Alternative Character Interpretation: The game is full of deep and multi-layered characters. Therefore, it's just natural that they can be seen in many different — and conflicting — ways. Of course, discussing this ventures into spoiler territory.
    • Frisk: Oh boy. Given The Reveal that Frisk is in fact an entirely independent entity from both the player and the Fallen Child, guesses as to their exact personality abound. Are they only responsible for the True Pacifist run, while Genocide is the result of Chara's corrupted self controlling them thanks to your actions? Did they choose Genocide and then lose control? Were they in control the whole way?
      • Not to mention, and even more disturbing, what the bloody hell ARE THEY? Chara will explicitly tell you that the determination comes from Frisk and not them (unless of course, the determination Chara was speaking for was directed at YOU, which only raises more questions), meaning this small child is so determined to survive they literally warp time and space to keep moving forward. Not only that, but they are inhumanly powerful. While the explanation of LOVE tearing through monsters is one thing, you can destroy Undyne and do defeat Asgore even without a drop of LOVE. And the "Monsters lose to LOVE" explanation falls flat when confronted with Photoshop Flowey and Absolute God of Hyperdeath Asriel. Both are the result of multiple human souls combining with one or more monster souls... and Frisk can rip them apart just as easily. Flowey gets away because of SAVE files, and Asriel because Frisk wants to Save them, but according to the lore, Frisk should have been powerless before them both.
      • There's also a question Asriel raises if you talk to him after the Pacifist Ending — why were they on Mt. Ebott in the first place, even though they most likely knew about the danger? Asriel hints that the Fallen Child didn't go there "for a very happy reason," but concedes that Frisk is a fundamentally different person.
    • Asgore: Is he a genuinely good person placed into an impossible situation who only did what he had to do; a wicked schemer who got away with several murders and planning the destruction of mankind; a coward unable to live up to his promises; or a coward unable to go back on an extremely bad, wrath-induced decision because he can't stand up to his own subjects?
      • Regarding his plan, did Asgore hesitate out of cowardice... or out of pragmatism and intelligence? Had he gone and attempted to take several human souls like Toriel suggested, it would have alerted humanity and despite Asgore's increased power, there was a chance he would've been injured or even killed and could have even led to the extinction of monsters. Then consider how much time could've passed since Asgore would've gotten the first soul and how humanity has advanced since then, especially when you consider the modern-day weapons humans would now have to slaughter monsterkind with. While he may not have wanted to go through with the plan at all, choosing to wait in the underground for any stray humans to arrive is more logical in the long run. While some would call it a long shot, considering that several children have made it there to fulfill the requirements in what seems to be a relatively short period of time, the idea still possessed merit. Furthermore, no one would bother looking for the missing people since they would be assumed dead, having died from falling into the mountain. He would've gotten the souls and maintained an element of surprise on humanity, and with how much time has passed, could've convinced his subjects not to wage war, since they finally made it to the surface.
      • Regarding his motives for making the plan. Does he actually want to take the surface back for the monsters? Does he simply want to give the monsters a new source of hope after the tragic loss of their prince? Or is he lying to himself and Frisk, and is revenge part of his motivations?
    • Toriel:
      • On relationships: Did she leave Asgore because she wanted nothing to do with his plans, to save the children that she knew would fall through the hole on Mt. Ebott, or did she have a problem just with the specifics of the plan and her husband being unwilling to go all the way? How much anger did she share with him over the death of their son, and to what degree has she mellowed out since then?
      • On personality: Is she just as bad as Asgore because, through her pacifism and relinquishing her crown, she essentially condemned the entirety of monster-kind to a futureless, bleak eternity beneath Mt. Ebott? Or does she believe that life underground is better for monsters than on the surface, given how one-sided the war was, and that the humans killed Asriel simply for wanting to return his friend's body?
      • Toriel condemned Asgore for his weakness, saying he could have taken one soul, left the underground, gathered six more souls outside, and opened the barrier that way, instead of waiting for humans to fall in and condemning the monsters to despair. Which begs the question of whether she would have wanted him to go kill humans to harvest their souls, or simply borrow the necessary souls from humans dying naturally; the ambiguity tends to make her come off much more bloodthirsty than him. In addition, when she said this, did she mean she actually supported the general plan, or was she telling Asgore to stop dressing up his actions as noble by saying that if he really wanted to save his people that way, he could have done it already?
      • Some have called Toriel on being a hypocritical coward since as Queen, she could've done the same thing using the Souls and rather than do anything, she ran away from her past and abandoned her husband onto a dark path while criticizing him for handling a complicated issue alone.
      • For that matter, is she a caring, healthy mother, or an overbearing, tyrannical control freak? She does resort to physical violence when Frisk disobeys her, and bakes the same pie regardless of how Frisk answers her question about flavors. Does Frisk matter to her as a person at all, or just as a thing she can impose her will upon?
      • If Toriel survives in the Neutral ending, she returns to being queen and decrees that humans must be treated as friends, but if you killed a fair number of characters, she'll be forced to abdicate and return to the ruins. Does she have stronger principles than Asgore does by virtue of refusing to let the demands of her subjects or her emotions sway her, or is she too weak-willed and ineffectual to lead well? Or is the political climate too hostile to the idea of peace after the death of a royal family member, which means neither she nor Asgore could have dissuaded the monsters from wanting revenge?
    • The neutral endings vary depending on how many monsters you kill (and who); Toriel is only forced to abdicate if you killed a lot of monsters. If you play the neutral more or less as a pacifist, the monsters are a lot more accepting of her new rule and law on humans.
    • Sans: Is he so lazy because that's just how he is, or because he knows everything he does could be undone at any moment and doesn't even bother trying? He even lampshades this during his boss battle.
      • Is he suffering from depression? Is this over his guilt at not being able to save anyone? Is it connected to Gaster in some way?
      • His awareness of the fact that he exists within a repeating timeline has inspired a lot of fan speculation and discussion in terms of how it affects him emotionally and psychologically, especially since he's intentionally meant to be a character that's difficult to get into the head of.
      • For that matter, is he truly aware of the other timelines? There have been numerous instances where he refers to the "glint" in Frisk's eyes and even makes mention of it before his boss fight. It could be that he's just reading Frisk and filled in the gaps.
    • There is an enormous range of interpretations of the first child who fell into the Underground, to the point where virtually every mention of them on this wiki contradicts every other mention of them. Most fanworks tend to depict them as callous and untrustworthy due to their Genocide route role being their only true appearance and their most memorable impact, but that's where the similarities stop.
      • It's clear that they hated humanity and wanted to get revenge, but what about monsters? Did the first child care for their adoptive family and want to help the monsters escape the Underground, or was that just a manipulative ploy? Were they always a monster (figuratively, not literally), or does the No Mercy path transform them into one as a result of the player's influence?
      • And why exactly did the Fallen hate humanity? Were they just a sociopathic jerk from the start, or did they actually have a good reason for such an attitude? Considering their official status as an extension of the player, both possibilities could be equally true.
      • Was the first child even human? Although they have been a soulless entity similar to Flowey/Asriel, were they really human to begin with? At the end of a second Genocide playthrough, they refer to themselves as a demon, but do they mean this literally, metaphorically (similar to how Asriel is dubbed "The Absolute God of Hyperdeath"), or did they end up that way through the player's actions? Was it even the first child themselves that set everything in motion, or were they possessed by something else, the way Frisk becomes if you play the Genocide route to the end?
      • An interpretation Played for Laughs is that in the corrupted Golden Ending, even though they're now possessing Frisk, they're not actually powerful enough to do more than Poke the Poodle. The prototypical example is to assume The Stinger you get in that ending is the entirety of Chara's exploits — if you stayed with Toriel, Chara... disrupts Frisk's sleep and possibly steals their pie. Or if you said you have places to go, Chara can't do more than vandalize Frisk's memento.
      • However, it's likely that Frisk's low LV is the reason Chara killed them all in The Stinger, since they need to increase their LV back to 20 again. Just how much power a LV 20 human possesses in comparison to other humans (and whether it means anything on the surface) is left unclear.
      • There are many hints littered throughout the game that the Fallen Child is the narrator of all the routes, not just the No Mercy route, because of how when the Fallen is in control, looking into the mirror results in "It's me, [Playername]" as the narration text, but when the Fallen isn't, it says "It's you!" or "It's still you, Frisk". If such an interpretation is true, then it adds a new layer to the Fallen's characterisation, as the narrator in the Pacifist and Neutral paths have shown a more dynamic, vibrant, and even sassy personality, and even seems to detest conflict at times, suggesting ways in which Frisk can resolve the battles peacefully. You can find a very well done in-depth analysis here.
      • This interpretation adds a whole new layer of sadness to the No Mercy route, as the player's bloodlust corrupts whatever is left of the fallen child from someone who helps Frisk through the Underground, despite their hatred of humanity, into someone who assists them in their slaughter of the monsters they once lived with and would kill Asgore, their adoptive father, without hesitation.
    • Why exactly did the humans wage war on monsterkind and seal them underground? The cave writings indicate that the monsters have no ideanote , but considering the fact that many of the monsters you meet are quite clearly not mentally stable by real-life standards, and the fact that there are entire species of monsters, like Vulkins, who don't realize how incredibly hazardous their mere presence is to humans, is it possible that the humans did it out of a legitimate fear for their safety, or perhaps in response to human deaths, accidental or otherwise, at the hands of monsters?
    • The main character's predecessors. Some of them are heavily implied to have taken the lives of multiple monsters before dying. It's left ambiguous what their reasons and motivations were, and plenty of people debate whether they killed those monsters for psychotic fun, or in legitimate self-defense since they didn't have Frisk's resetting powers and thus had far more justification to use lethal force in defense of their life, or if they were the aggressors, but did it out of a tragic desperation to escape the underworld and avoid being used as a weapon through which to exterminate their own species. Most agree it probably wasn't a uniform reason between all of them and that between all six of them, all of these reasons and more could have been behind their actions.
    • W.D. Gaster: what does he want? Because so little is known about him, a multitude of interpretations exist in fan content. A lot of it has Gaster as driven insane by his condition or seeking to return to life even if it is at the player's expense, some portray him as Creepy Good (especially when it comes to laying the smackdown on a No Mercy player), some have him either antagonistic or heroic depending on the circumstances, and in others he is just... weird.
    • Do the monsters naturally want revenge on humanity, or are they going along with their beloved and well-respected king's decision? Gerson says that he agreed with Asgore's decision to stay underground instead of risking a second Hopeless War with humanity, and "felt a little betrayed when (Asgore) eventually changed his mind," but comes around on the Genocide route, when a human's killing them anyway. This could suggest that some of them could accept life underground as safer than the alternative, or that the right circumstances could change their minds. However, the game also says that Asgore's motivation to keep going with the plan was to keep morale up because he believed that the hope of exterminating the human race and reclaiming the surface was all that kept his people going. So either this theory is completely false... or this entire story is a colossal tragedy of miscommunication, with both sides at least partially claiming to support the genocide because they feel the other side wants it.
  • Angel/Devil Shipping: While it's debatable whether or not Asriel would be considered a Devil to Frisk's Angel, this trope is played straight with Frisk x Flowey and Frisk x Chara during the Genocide run.note 
  • Angst Aversion: Not the game itself, which, when played as a Pacifist, is quite uplifting, but with the Genocide route. A lot of players, especially ones that got especially attached to the characters, actively avoid it (and any fanart and fanfic surrounding it) because they just find it too sad.
  • Angst? What Angst?: In the epilogue of the True Pacifist route, the Dogi seem completely unfazed by all of their parents having been merged into an amorphous, faceless and mindless creature. Ditto for Drake and his father in regards to what happened to Drake's mother.
  • Annoying Video Game Helper: Given her attitude towards the player, her role, her Punny Name and the game's nature as a Deconstructor Fleet, Toriel is likely intended as a satire of the obligatory annoying tutorial character that tells you stuff that should be obvious even to a goldfish. She literally holds your hand through at least one puzzle! However, unusually, it's all Played for Laughs and kinda heartwarming more than it is annoying.
  • Anti-Climax Boss:
    • While it doesn't seem like it at first, the Photoshop Flowey battle is actually heavily skewed towards the player. Sure, Flowey's Bullet Hell is the strongest of any boss in the game, but getting hit only cuts your health in half, so you have to be hit plenty of times (14, to be exact) to actually die. The SOUL sequences (which take up about a third of the battle) are actually impossible to die to, and clearing them grants you a ton of healing and a checkpoint for if you die. Once you call out to all six SOULs, the battle is pretty much over; the now vulnerable boss has a so-so health pool and you're showered with green healing bullets while you attack. While it's very likely you'll die several times until you learn how the attacks work, overall the preceding fights with Mettaton EX and Asgore are tougher despite feeling less so, especially if you have low LV. It manages to be a very cool boss fight regardless.
    • For those who expect a challenge at the very end, the final battle from the Pacifist route can be disappointing due to two factors: You can not only "dream" for virtually endless healing items, but it's actually impossible to lose the fight since you end up reviving each time you die. The fight can be especially jarring if you've done the No Mercy route first, since the Climax Boss found there is the hardest fight in the game. That being said, the other factors of the fight are not disappointing at all.
    • While this trope is invoked on the No Mercy route due to the fact that you can kill all but one boss in one hit, the fight with Mettaton NEO stands out in particular. He gains a new form not unlike Undyne the Undying, so in theory he should be a serious threat. In practice, he not only dies in one hit like the other bosses, but he doesn't bother to attack you.
  • Anvilicious: In part due to Hype Backlash, some people have felt the whole moral of "Actions have consequences" was a tad obvious, and since other RPGs have done it as well, to the point of being BioWare's calling card as a company, it could come off as tired.
  • Award Snub:
    • While Undertale getting nominated for any Top 5 at the 2015 Video Game Awards is amazing in and of itself for an independent game released late into the year, the games that were chosen over it were somewhat baffling to many of the viewers. "Best Independent Game" itself was won by Rocket League; most of the fans pointed out that Rocket League might be a perfectly fun game, but it is a multiplayer sports game that, unlike Undertale, doesn't try to tell a story, make any artistic statements, nor toy and experiment with the conventions of the game medium. Additionally, Undertale wasn't even nominated for "Best Narrative," which ended up going to Her Story, or "Best Original Score", which went to Metal Gear Solid V: The Phantom Pain.
    • It is notable that Zero Punctuation outright defied the trope. In the Top Games of 2015 episode, Yahtzee pointed that he only placed games which he had already reviewed on the best games list. Having not done a review on Undertale previously, he then quickly made an impromptu review (literally just him stating that "Undertale is a good game!"), and he went on give Undertale the "Best Game of the Year" award.
  • Awesome Ego:
    • Papyrus thinks he is the most awesome person in the whole world. You still can't help but love him because he's always unflinchingly nice and helpful to everyone. He never looks down on people with smug superiority, but wants to help everyone else be almost as awesome as he is! (Equaling him is impossible.)
    • Mettaton. Just about everybody both in-universe and out thinks he's absolutely delightful.
  • Base-Breaking Character:
    • So Sorry. Some players absolutely despise them for being a furry Self Insert, and think they ruin the game. (The character was one of the ones added by via a generous Kickstarter donation; the donater happened to be a furry and contributed a simplistic version of their own character to be used as So Sorry.) Some players think hating them is an absurd stance. Some players admit that a furry self-insert isn't something they want to see, but don't mind that So Sorry exists since they're very hidden and very optional, so they don't have to. Accordingly, every mention of the character is liable to spark a flame war.
    • Alphys. A lot of players find her character gimmick of constant messages and attempts to help more annoying than funny, especially on repeat playthroughs. And even though she has sympathetic reasons, the reveal that she's been experimenting on sick monsters to create the Amalgamates and manipulating the player to feel better about herself doesn't help, especially since she never directly apologizes for the latter.
    • For the Temmies, there are four groups: those who love them and think they deserved more of a presence, those who found the gag funny but are glad it was kept to a single area, those who find it a lame attempt at "lolsorandom" humor that the game otherwise avoids, and those who think they're overly blatant Mr. Saturn expys.
    • Asgore is either beloved by fans who find him a very likable character who was put through a very difficult situation and ended up making major mistakes due to it or hated for the same reasons Toriel hates him. It doesn't help that he's often a victim of Die for Our Ship as well.
    • Sans has become this as his popularity's reached a fever pitch. The amount of fanart and fanfic focused on him dwarfs all the other characters, complete with numerous AUs centered around different versions of him (and AUs of those AUs) sometimes shipped with each other, and even entire original series inspired by the many different Sanses. Various jokes about his astounding popularity, including comparisons to the Once-ler fandom abound. As a result, a backlash is developing among other fans who perceive that he's becoming to Undertale fandom what Wolverine is to Marvel at the expense of the game's other characters, especially since so many AUs and fan scenarios feature Sans taking their place in the story, alter their personalities or backstories in order to make Sans look better at their expense, or even have them Stuffed into the Fridge altogether to make more room for Sans when they're not being ignored completely. Adding to this are also people who do like Sans, but dislike the fandom response to him because of all the Canon Defilement and Mary Sue Tropes surrounding him (or think that, while he's an interesting character, he takes attention and focus away from other characters who might deserve it more). Not helping things is people thinking the concepts behind many of the broader-encompassing AUs are interesting and have great potential for storytelling, but, barring a few exceptions, a large number of them explore only Sans.
  • Best Known for the Fanservice: For the Furry Fandom, regarding all the animal-looking characters. The Ice Wolf and the Hotland Royal Guards receive special attention.
  • Big-Lipped Alligator Moment:
    • Onionsan's appearance. He shows up, rambles on as you try to walk along the river, has some dialogue choices that don't really make any kind of an impact, and that's the last you ever hear of him. Don't ask Toby about him; not even he knows. Additionally, calling Papyrus or Undyne in his area will just net a confused "Onion...?" from both of them. Yep, they're just as confused as you are.
    • Muffet. She appears essentially from nowhere (her appearance selling spider food looks more like a quick joke than anything else), and unlike other boss fights, hers has almost no relevance to the plot. She alludes to Mettaton's obstacles being an act, but not in a really obvious way. She leaves the plot almost as quickly as she enters it, only seeming to serve as a way to pace the game better. This could be justified in that Muffet was a character that was added into the game due to Kickstarter donation, which could explain why she doesn't fit in. She does, however, have more relevance in the No Mercy Route, where her refusal to leave her spider nest behind creates a route for the player to progress through, where otherwise the player would have been trapped with no way forward.
    • Solving the piano puzzle in Waterfall leads to the Annoying Dog stealing the artifact and flying away while the dog song plays in the background. While he leaves behind Dog Residue that could be used to farm money, the scene to begin with is nonsensical and has no bearing on the plot — especially if it's done on No Mercy.
    • The... whatever-it-is that happens when you lay on the floor of Napstablook's house. While pretty and ultimately very soothing, it's a bit out of nowhere and never explained in-game.
    • Temmie Village is entirely possible to miss and has no bearing on the game if you do, the Temmies are, frankly, really weird, and their village is about as odd as you can expect, their history is a picture of a Temmie riding on a dragon with no additional context, one of them breaks out in hives only upon mentioning said allergy to itself, and another is trying to incubate a hard-boiled egg.
    • To a lesser extent, Memoryhead in the True Lab. They're the only Amalgamate that doesn't obviously resemble any of the monsters you've previously encountered, unlike the others, and they seem to act like some sort of living glitch (their speech is garbled and blocky, the battle text itself is random, and most of the ACTs are from your non-battle menu). Since their appearance resembles a cross between skulls and Giygas, this has led to people wondering if Memoryhead is related to W. D. Gaster in some fashion.
  • Broken Base:
    • The fanbase cannot agree on what name fits the Kill 'em All route better. The more popular choice of name is the Genocide route, since this is exactly what the protagonist does; however, some of the fanbase feels the name is too much of a spoiler, and call it the No Mercy route instead. Those who prefer the name "Genocide" argue back that the "No Mercy" name is too vague and fits other routes of the game better (such as the one where all the bosses are killed but none of the monsters, or one where all the bosses and some of the monsters are killed). A few Take a Third Option and call it "Max LV" (due to the latter resulting inthe player hitting the LV cap) or "having a bad time" (after a creepily-delivered line from an NPC warning the player not to continue their murderous ways).
    • There are those who are split on whether the game's story and overall message is amazing and refreshing or if it's average at best or poorly executed at worst. This is held especially true for the pacifist route regarding Asriel. On one side, you have people who feel that the story doesn't live up to the message of "don't kill and be kind to people" because Asriel was slain by humans after he tried to bring Chara's body back to them out of respect. On the other end, you have those that feel that the aspect of being and doing good is what matters the most rather than what the end result of it brings and how some people simply cannot be saved no matter what you do because that's how life is.
    • Some fans are divided over the Genocide route tainting your game forever. There are workarounds to purify the game, but some people are annoyed at how far out of their way they have to go to enjoy the game their way. The other camp is annoyed at the first group for rejecting the message of "you aren't above consequences."
    • On a similar note, whether or not players should be encouraged to go for the Genocide Route. Many argue that it's a part of the game that must be played in order to get the full experience and not playing it is an injustice to the game. However, the fact that the game repeatedly discourages the player from doing this (especially after achieving the Golden Ending) and heavily guilt-trips them if they do and, as mentioned above, will permanently taint the game with a Happy Ending Override on any future Pacifist runs should they complete the Genocide route has led others to feel encouraging newer players to play the route is overly cruel. (Also, the Genocide route's messages hit the hardest for players going into it willingly.)
    • Discussing Mettaton's gender is often fuel for flame wars on a massive scale; while Mettaton is referred to as he in the game (unlike characters like the Human Child and the ghosts, who both in-game text and characters are content not to specify and the latter of which are actually the same species as Mettaton, making him the only ghost who's gendered in the game), his effeminate behavior and rather... flashy EX form have lead to many an instance of Viewer Gender Confusion among more casual fans and been played in arguments over just what he identifies as.
      • Relating to this, there's whether Mettaton "counts" as being transgender or not. His change from being a ghost to possessing a robot body is referred to in his diaries in similar terms as a gender transition might be, enough that if nothing else there's a case for him being a transgender allegory or trans equivalent of the Discount Lesbians trope of sorts, and is combined with his pronouns changing from a gender-neutral they/them/their into he/him/his - for some fans, this is enough for them to feel that he canonically counts as transgender representation, while others actively deny that gender is even an issue with his character. People on both sides can be incredibly aggressive about the whole thing.
    • There's a decent point of conflict within the fandom over Asriel and his ultimate fate in the Pacifist Run. Some fans argue that his actions as Flowey don't make him worth having his own happy ending, or believe that him staying in the underground as a redeemed but still emotionless flower is suitable penance, or that there needs to be one last moment of bittersweet to keep the ending from being insufferably Tastes Like Diabetes. The other side... well, the amount of Fix Fics that have Asriel saved, one way or another, should tell you that there's a massive crowd who thinks absolutely everyone should get their happy ending, even him.
    • There's also the Internet Backdraft over Frisk's canonical identity. Is Frisk meant to be a Featureless Protagonist Player Avatar, and therefore whatever gender the player is? Or is Frisk always and only ever their own person who refuses to identify as male or female?
    • Mentioning a sequel is usually a surefire way to get the fanbase fired up. One side believes that the game's Golden Ending should remain as is (thus no sequel), while the other side feels that the game can expand upon a sequel and that there's room for it.

    C-E 
  • Character Exaggeration: A lot of characters have been subject to this by fans. Sometimes it's intentional for the sake of comedy, but other times it's not.
    • Sans in game is a Lazy Bum with a penchant for puns, but he'll repeatedly kill you in hopes of making you Rage Quit. In his boss fight and in the Asriel fight, it's made clear that's he's been pushed past the Despair Event Horizon, but it wouldn't be too clear otherwise. He also cares about his brother. One of five things tends to be exaggerated (and sometimes, it's more than one).
      • Sans is too lazy for his own good. To the point that he'll fall asleep while doing extremely simple tasks.
      • The only jokes Sans knows are puns.
      • Sans is incredibly overpowered, to the point where it's impossible to beat him.
      • Sans is openly depressed and literally no one notices. note 
      • Sans is a Knight Templar Big Brother. To the point that he'll kill you for even insulting Papyrus.
    • Papyrus is full of himself, but not to the point where he's unbearable. He also makes spaghetti because he thinks people like it (though he's bad at it) and he makes lots of puns of his own (especially in phone calls), while mostly finding Sans's puns to be bad due to overexposure or otherwise. However, according to the fans, puns are Papyrus's Berserk Button and he'll fly into an Unstoppable Rage after hearing one, he makes spaghetti because he likes it, and to him, It's All About Him.
    • Mettaton's subject to this, not only in personality, but in looks. On the latter, in the game, he's beautiful in the way David Bowie was. To the fans, he's beautiful in a way a woman is. Likewise, on the former, fans sometimes downplay or nix his cutthroat edge and cocky attitude and bend his theatrics and flamboyancy for less of a "gender-bending showman" demeanor and more of a Sassy Gay Friend one.
    • Toriel's clearly not on good terms with Asgore by the time they reunite within the game, but the epilogue does have hints that they may, in time, mend their relationship. Not so according to some fans, who portray her going into a bloodthirsty rage at the mere sight of him.
    • Speaking of Asgore, he, in the game, is a Gentle Giant who, while he does miss his family deeply and wants another chance, understands why Toriel left and hates him. The fans, however, see him as a full-blown Yandere to Toriel, doing anything and everything he can to drag her back to him.
    • While Frisk's morality is still in question, fan's agree that they are an Actual Pacifist, even though you can play as them in a particularly violent neutral run or genocide run. Even in a Golden Ending-pacifist run, they can still show some jerk traits (insulting Papyrus, eating the snowman piece right in front of the snowman, refusing to save Monster Kid, etc) as well as attack a given monster without killing them.
  • Common Knowledge:
    • 'Determination' is often cited with full confidence as the 'trait' for the red SOUL, however in-game the red SOUL's trait is never stated and furthermore, it's mentioned several times over that all humans have Determination. Also in-game the only color Determination is assigned is yellow (In Alphys' True Labs entries), every other time it's mentioned it gets plain white text and it isn't listed with the other traits during the Ball Game, although curiously enough 'Ball Game' is written in red text should you beat it with every other color.
  • Counterpart Comparison:
    • Undyne has a lot in common with Adventure Time's Marceline: both are Action Girls, Hot-Blooded, Cool Big Sis, and the list could go on. Plus they have very similar clothing: jeans, a dark tank top and red boots.
    • Flowey can give some players a certain reminding of Kyubey. The grotesqueness of his powered-up form can also remind some players of the anime's witches.
      • It's also noted that much of what Flowey says wouldn't sound out of place coming from The Joker. His obsession with tormenting the player character and desire to goad them into killing can also be seen as a mirror of the Joker's obsession with tormenting Batman. Even one of Flowey's Nightmare Faces looks like the Joker's face.
    • Sans is frequently drawn as Jotaro Kujo of JJBA, due to his ridiculously hard boss battle, association with the color blue, and one scene where he seems to have the ability to stop time. More often than not, his Gaster Blasters will be his Stand.
      • Aided by the fact that their games are similar and have a lot of mutual fans, many people have also noted a lot of similarities between Sans and Pablo, a.k.a, The Judge; both perpetually sport toothy smiles, are friendly but have strong moral codes, have younger brothers that they love dearly, are sent into a Heroic B.S.O.D. upon said brother's death, and confront the player for their evil deeds at the end of their respective games, potentially serving as the final boss. Sans's final confrontation is even referred to as "[being] judged", thus making his unstated title the same as Pablo's.
      • Taking this a step further, the Genocide route of Undertale could be thought of as a counterpart to the canon route of OFF. Both have notable similarities (such as the player killing everything in their way and destroying the world) that make one wonder if the parallels are intentional.
      • If you consider the game to be a modern-day version of Alice in Wonderland, Sans is very much like the Cheshire Cat. After the child falls down the hole, he greets the child from the woods; he is friendly, but sometimes acts as a distraction, to the point of trolling; he has a fondness for wordplay, can move from place to place in the blink of an eye; and of course his perpetual grin. The player's final confrontation with Sans (in a castle hall just before the battle with the monarch) is eerily similar to the Cat's death in American McGee's Alice, except that if Sans dies, it's at the child's hands.
    • Most characters of the game have been compared with the characters of Wander over Yonder for having at least one major similarity. The character that is compared the most is Papyrus with Lord Hater for both being skeletons with similar character traits, with the only difference being that one of them is evil. Mettaton has also been compared with Emperor Awesome from the same show. Another Wander character, Lord Dominator, gets this with both Undyne (with strong Good-Evil Counterpat vibes) and the Fallen Child in the Genocide route.
    • The Amalgamates are very often compared to the Gem Clusters from Steven Universe. Ironically enough, Steven Universe also has a music track called "Amalgam" concerning fusion, but the tone between the two is radically different.
    • Toriel, with her color scheme and similar clothes, has been compared to Ran Yakumo or, rather, the motherly fanon portrayals of her.
    • The very premise of the game (a child falls down a hole and finds a vast underground world) is similar to the premise of The Great Cave Offensive from the 1996 SNES game Kirby Super Star; in The Great Cave Offensive, Kirby falls into a hole during a hiking trip and ends up in a vast underground world full of treasure. Adding onto this is the fact that both Undertale and The Great Cave Offensive feature antagonistic sentient flowers that show up very early on (Flowey and Lovlies, respectively).
    • The Fallen Child, who hates humanity, befriended a member of the opposing species, and wants to shatter the barrier between worlds and die doing so, has a fair number of similarities with Shinobu Sensui from YuYu Hakusho.
      • The Batter is commonly associated with the Fallen Child as well. They both want to erase the world, after all, and both are also known for Playing the Player.
    • Despite being based off of John Kricfalusi's art style, Burgerpants - with his disdain for his job as a fast food clerk, strained hopes of becoming a star, and general grumpiness - is frequently likened to Squidward.
    • Some fans have noticed a very strong similarity between Mettaton EX and Jewel Man as both are robots with very vague narcissistic personalities, and right down to very similar designs. Some even nickname Jewel Man "the original Mettaton."
  • Crack Pairing:
    • Gaster is a huge launcher of many of them, including Gaster/Asgore, Gaster/Grillby, and Gaster/Alphys. This is largely due to the fact people are shipping a character who doesn't exist with ones who do.
    • A tag glitch on Fanfiction.Net once resulted in "Sans" being listed as a pairing for one story. Just Sans, by himself. This became a fandom in-joke, and Toby Fox even once joked that it was his favorite ship.
    • There are even people who ship Alphys and the Amalgamates (some of which, like Reaper Bird and So Cold, are barely sentient).
    • Undyne and Muffet, two characters who never meet or interact in-game (and one of which is canonically in a relationship), have gotten some fanart.
  • Crazy Awesome: Frisk in a full-blown pacifist run takes being a Badass Pacifist to its logical extreme and blows past it in some areas. It takes a special kind of craziness to get certain monsters to spare them by hugging a talking mini-volcano, running toward a sentient airplane, or playing fetch with anthropomorphic dogs that are armed to the teeth.
  • Creepy Awesome:
    • Is Flowey a terrifying character? Yes. Is he also a Magnificent Bastard who plays all his cards right? Also yes.
    • Flowey kicks it up a notch in the neutral run when he turns into Photoshop Flowey, a form that turns him into a complete Eldritch Abomination. However, his complete mucking around with Save Scumming and the his massive amount of screwing with the interface makes him a pretty badass boss.
    • Then there's the Amalgamates, combining the features of several undead monsters into a highly disturbing something that may or may not be suffering through worse than hell. They are only encountered during True Pacifist in one of the bleakest areas of the entire game, are mostly not quite easy and definitely horrifying to fight, and in at least one case really cuddly.
  • Creepy Cute:
    • Muffet, a murderous spider girl with an adorable design.
    • Some of the Amalgamates can become this once you realize they're just as innocent as all the other monsters. Most notably the dog Amalgamate, Endogeny.
    • The Fallen Child. In the Genocide Route, they're a cute, smiling child that's become an unrepentant mass murderer. Doesn't help that a lot of fanart portrays them with various degrees of aging-up and physical attractiveness.
  • Crosses the Line Twice:
    • If you kill Tsunderplane, it starts plummeting down while saying "but I never got to-" before crashing and exploding.
    • Jerry is made obnoxious in so many ways that he wraps around into being a Love to Hate character instead.
    • In a masochistic sort of way, getting dunked on by Sans is likely to be frustrating and unexpected for new players, and having your trust be betrayed by the game is extremely startling in a meta sort of way. But the fact that the Non Standard Game Over is accompanied by Dog Song, one of the silliest songs in the game sped up to be even sillier, takes a bit of sting out of the wound and instead makes the experience Actually Pretty Funny.
  • Crossover Ship: A few, but two that stand out are Frisk and/or Chara with Madotsuki due to all of them being children in EarthBound-esque games with an affinity for knives, and in Frisk's case sharing identical facial expressions throughout the entirety of their respective game.
  • Die for Our Ship: Asgore is bashed a lot by the more hardcore Sans/Toriel shippers due to already having a pre-estabilished relationship and later fall out with the latter, not helping matters is that Toriel provides a lot of ammo for shippers to use in their bashing against him while making Sans sound like the ideal partner.
    • Toriel also gets the same treatment from others, often claiming that she left Asgore not for the totally sympathetic reasons she's stated to have left him for, but for petty irrational reasons brought on by a complete breakdown following the death of their son.
    • Frisk/Asriel shippers tend not to be very nice to Chara, often downplaying or downright writing out all of their sympathetic qualities and twisting them into an uncaring, abusive jerk who doesn't care about Asriel at all despite the heavy in-game evidence against this, and sometimes going as far as to rewrite the entire backstory in order to make it so Chara and Asriel were never really friends just to make Frisk look better. Even when they're not being demonized, shippers almost never fail to have Asriel make some sort of snide remark at their expense.
  • Draco in Leather Pants:
    • While Asriel isn't necessarily evil enough as himself, Asriel as specifically his insane God of Hyperdeath form, when he is decidedly still a villain, has a lot of fans who like him more than his true, redeemed self.
    • Toriel. While she's not a bad person, the fact that she treats the player character so kindly at the beginning of the game makes it easy to overlook that she basically attempted to abduct a child with lethal force and treated her ex-husband Asgore questionably. She's also an example of Base-Breaking Character since some of Asgore's defenders take it too far and make a Ron the Death Eater out of her.
    • Depending on the mass amounts of Alternate Character Interpretation and complete utter lack of in-game evidence supporting any side, the Fallen Child may be an example of this. While there's some precedence for this in that they had a (unsaid) reason for wanting to disappear and aren't a world-destroyer unless you, the player, guide them towards being one, they still weren't "the best person" according to Asriel, and they've undeniably become an evil Omnicidal Maniac by the end of the Genocide route. In spite of this, many fans portray them as simply being misunderstood in life and still not being wholly corrupt even after destroying the world and taking Frisk's SOUL.
  • Enjoy the Story, Skip the Game: A general consensus among casual fans says this: while the game is worth playing for the story, the actual gameplay is decent at its best and boring at its worst. What makes this worse is that the game itself discourages players from replaying it, especially if they reach the Pacifist ending.
  • Ensemble Darkhorse:
    • Muffet. Her adorable and well-done design, interesting personality, difficult yet fun and interesting boss fight, and great song for her battle make her a lot of people's favorite minor character. There's just as much fan art for her, if not more, than Toriel. It might help that she's designed by Michelle Czajkowski of Ava's Demon fame.
    • Everyman, part of an attack done by one of the Amalgamations, is also becoming surprisingly popular, especially after being given an official name by Toby, despite being no more than a bullet in another enemy's bullet hell. It's even considered an icon of constant speculation source Dr. Gaster.
    • "Burgerpants," the cashier at MTT Burger, has gotten a fair amount of love for his desperate and miserable demeanor and goofy expressions, on top of being a character that those who work in the fast food industry can relate with. On top of being one of the very few characters that aren't scared of the Fallen in the No Mercy route.
    • The Royal Guard Dogs in Snowdin, but particularly Doggo (who has been very popular with the Furry Fandom) and the Lesser Dog (for his neck-stretching antics). Even Toby seemed surprised that Doggo became so popular.
    • Ice-E, the mascot character for Monster Kidz Word Search, has enormous popularity in comparison to his relevance (appearing in one scene as a picture).
    • The Temmies appear in only one location, but are widely popular for their cute design and adorable quirks, often being called the Mr. Saturns of Undertale. The shopkeeper Temmie is especially popular for both providing the best armor in the game and its Surprise Creepy moments.
    • Woshua, who's just a random encounter, but is popular among the fandom due to his amusing speech patterns, character gimmick, and some hilariously dark dialogue, which have caused him to be regarded as a self-appointed memetic Moral Guardian.
    • Snowdrake is another random encounter who's quite popular due to his adorable design and So Bad, It's Good puns, as well as his backstory making him a huge Woobie, as well as being one of the most tangible examples of Video Game Cruelty Potential if you choose to kill him.
    • Rather coincidentally, all three of the "fire elemental" NPCs count. Grillby is loved for being one of the few named minor characters, having a unique design, and there being plenty of room for fans to develop him (particularly with his relationship with Sans). Heats Flamesman is liked for providing a random, hilarious moment, even getting a flair on the Undertale subreddit. And the fire girl in a Sailor Fuku in Hotland is liked just for being adorable.
    • Perhaps the strangest example out of all of these, the Yellow Soul, due to the prevalent 'yee haw' meme on Reddit.
    • Of the side characters who don't have a bearing on the plot, Napstablook is adored for being huggably sad all the time, having a jazzy boss theme, saving the player from the Mad Dummy, and the weird yet awesome moment that happens if you choose to hang out with them.
    • Madjick also has a bit of a following, seemingly for no other reason than it was a running joke that somebody started.
    • The Annoying Dog, who most players will find more amusing than annoying due to the ways it trolls the cast, such as apparently being one of Papyrus's death traps and sneaking into the player's inventory and then absorbing a "legendary artifact" when deployed.
    • The Tsunderplane, for being a parody of Tsunderes. Not that it likes being popular or anything!
  • Epileptic Trees: The community as a whole believes that the "trait" corresponding to the red human SOUL (as in Blue=Integrity, Yellow=Justice, etc.) is determination. The Ball Game, which provides SOUL color lore, doesn't explicitly name a trait for the red SOUL, instead listing the traits of the other SOULS or saying how the player "continues to be themself." The only place in the game where this is implied is where Asgore says that Frisk and the First Human share the same feeling of hope in their eyes, while they both have a red soul as indicated by the First Human's coffin
  • Esoteric Happy Ending:
    • The Golden Ending in general is quite positive, but the Amalgamates returning to their families to live happily seems out of place, considering the horror attached to their reveal and the Body Horror they experience.
    • As mentioned under Fanfic Fuel, Flowey/Asriel's fate rubs a lot of people the wrong way, and somewhat diminishes what would otherwise be a literally perfect ending for everyone.
    • A similar, but far more subtle and subjective case could be made about Sans. He explicitly states at the end of a genocide route that it doesn't matter to him if he makes it to the surface or not - he's been so conditioned by Flowey/the player's continuous resets that making it would just feel like a false hope being dangled in front of his face. The question here is a matter of Alternate Character Interpretation; was he only saying that because he was at his Darkest Hour, and has enough faith in the protagonist/player by the end of a pacifist route to enjoy life on the surface like everyone else, or will he spend the rest of his days just as depressed and nihilistic as before?

    F 
  • Fandom Berserk Button:
    • Discussing the protagonist's Ambiguous Gender will often lead to some very nasty flame wars on such sites as tumblr and the like, as the mystery is intended to be that way according to Word of God.
    • So Sorry's existence is a huge sore spot for the fandom to the extent even mentioning the guy sparks flame wars between those who hate him and those who wish the haters would stop bashing him and move on.
    • Try criticising the game in general or say you liked another game better in 2015 and the heat of a thousand suns will be felt from the (ahem) louder part of the fanbase. Unfortunately, this has resulted in a lot of backlash against the fandom as a whole, with its chill, friendly portions getting the same reactions as the overzealous ones from people who've seen too much of the latter.
    • An especially nasty one that Let's Play-ers often face: Playing a Neutral run, either on purpose or out of ignorance. Expect the comments section to be aflame with fans lamenting the deaths of NPCs and perfectionists demanding that the player restart the game and perform an absolutely flawless Pacifist Run, even if the player made it clear they wanted to play the game blind. Note that this makes a True Pacifist run completely impossible, since it can't be done on a first playthrough.
      • One huge Berserk Button seems to be killing Toriel on a Neutral Run, as Dookieshed puts it. He even lampshades this with how the title "Why You Should Kill Toriel" is clickbait, and argues that Undertale is a game that needs to be experienced, at the risk of the player not doing a full Pacifist Run.
      • As an example, popular YouTuber Mangaminx ended up on the receiving end of this. It soured her opinion of the game and the hype surrounding it, though she still completed the Neutral playthrough just to spite her detractors. The fact that she has a low opinion on games with Multiple Endings to begin with (which Undertale is) doesn't help either.
    • Tell somebody who believes the Fallen Child is the true villain of Undertale that the Fallen Child was really the Narrator All Along or vice versa.
      • Or worse, tell either of them the Fallen Child was really the Anomaly and the true Player Character.
    • Complaining about being stuck on the puzzles. Since the puzzles in the game range from jokingly easy to only mildly difficult, and given that many puzzles will just let the player pass through if they fail a few times, complaining about the puzzles being too hard tends to indicate that the complainer didn't try at all.
    • There was a period when calling the Kill 'em All path by the "wrong" name was a good way to experience a Flame War. Both "No Mercy" and "Genocide" were considered the "wrong" names for various reasons, and most other names were originally coined as third options for people sick of the debate. Nowadays, the fandom mostly acknowledges that there is no official name... so asserting that one name or the other is "correct" is the new flamebait.
  • Fandom Rivalry:
    • While not as heated (note that OFF is also under Friendly Fandoms), some discussion has also happened between this game and the fandoms of LISA and OFF, two other indie RPGs that deconstruct the genre of RPGs and put heavy emphases on consequences for actions.
    • There has been some argument between fans of this game and of Homestuck, mostly concerning the music track "Megalovania" which appears in both.
    • Thanks to Toby tweeting about the game's Metacritic rating (a good 95+), there have been heated discussions involving it and the equally rated Metal Gear Solid V: The Phantom Pain.
    • Thanks to an organized rally by Undertale fans, mostly on Tumblr, to advance the game in GameFAQs's "BEST. GAME. EVER." poll, resulting it in winning the poll, some Nintendo fans have cried foul after that led to it beating out classics like Super Mario World, Pokémon Red and Blue, Super Mario 64, Super Smash Bros. Melee, and The Legend of Zelda: Ocarina of Time. Part of the issue is that Undertale's initial entry into the contest at all was because of a confirmed bot flooding votes. While the game managed to keep gaining traction on the strength of its fans alone, the controversy surrounding its nomination has caused a lot of genuinely sour feelings towards the game and the fandom. This has come to a head with the Legend of Zelda fandom, when Undertale beat Ocarina of Time for "Best Game Ever." This hasn't been helped by fans of both games being incredibly sore winners/losers.
    • The Five Nights at Freddy's fandom is probably the worst offender of them all. Since both are indie cult favorites turned mainstream hits, many nasty conflicts have arisen between the two groups.
    • The Cave Story fandom tend to be annoyed if Undertale shows up in the "Cave Story" Tumblr tag, generally viewing this game as a successor to Cave Story, or unfairly having the popularity that Cave Story should. Regardless, many more like the idea of a Cave Story/Undertale crossover.
    • While the Steven Universe fandom normally gets along quite well with the Undertale fandom, as seen below under Friendly Fandoms, there is one thing that gets Steven Universe fans upset with Undertale fans. The song "Stronger Than You" sung by Garnet in the Steven Universe episode, "Jail Break", received a fan-made parody set in the Undertale universe sung by Sans. The parody is extremely popular with Undertale fans. In fact, its popularity is so great that the parody comes before the original Steven Universe song in search engines, and some people even think that the parody is the original.note  Needless to say, Steven Universe fans and Undertale fans who have Hype Backlash towards Sans were not happy with the result.
    • These days, ironically the EarthBound fandom. People got tired of people bringing Undertale up in all MOTHER/EarthBound discussions, and some places ban all mentions of the game entirely.
    • Many less mature Homestuck fans are rather aggressive in their dislike of Undertale and its fandom, mostly thanks to ire over MEGALOVANIA's usage and subsequent explosion in popularity causing many to assume it came from the game, when it was in fact featured within Homestuck several years prior. note  This is notably mostly rather one-sided, with the majority of Undertale fans bemoaned by these people likely having little clue on Homestuck's existence for the most part.
  • Fanfic Fuel: A truly massive amount of it, given what other fandom Toby works with, it's likely that there was just enough of a lack of answer to a lot of questions deliberately to give fans stuff to write about.
    • With the True Ending allowing the monsters to access the human world, many fans are already coming up with ideas about how they manage in the outside world.
    • Whoever the six Human SOULs were and what they went through before their inevitable deaths is good fuel for speculation, as well.
    • A popular What If? scenario involves switching Sans and Papyrus' places in a No Mercy run, speculating that if Sans was killed first by the player then Papyrus would have either turned into a vengeful badass who "no longer believes in you" and gives you "a bad time" or a broken skeleton who is still too good-hearted to unleash his full power.
    • The skeleton characters have this in spades, from Sans's Breaking the Fourth Wall and Crouching Moron, Hidden Badass powers to the hidden Dr. Gaster and how he met his fate. Sans's awareness of the fact that he's in a repeating timeline is very open to interpretation as well, with many a fanfic exploring the psychological and emotional effects it would have on him, speculating on exactly how much he's able to remember, and making What If? scenarios in which he (and sometimes other characters) are able to remember them fully.
    • Because the Golden Ending still leaves one character, Asriel, in a tragic situation, a common setting for a fanfic is about abusing the timey-wimey nature of SAVING and LOADING to truly save everyone. The ones that don't have Frisk "fix" Asriel's soul usually involve Flowey getting uprooted, stuck in a flowerpot, and living with Frisk as a sort of "vile houseplant".
    • The Fallen Child's backstory, since it's never truly answered in game. Were they really out to unseal the barrier and free the monsters, or was it a ruse to destroy everything? Were they evil all along, or did they just have a Dark and Troubled Past? What is their relationship to Frisk: as a guide and mentor, or as a parasite?
    • A less notorious What If? scenario is Alphys getting her own boss fight during the No Mercy path. One particular interpretation (which also is a kind of Memetic Badass) is her piloting a giant robot called Mechalphys, a cross between a Starman and the R7000 series, which got popularised after an idea that the DeviantArt user hfbn2 came up with.
  • Fan Myopia: It was hit with a very strong case of this wherein people constantly overblew how important the game was, as well as their own fanon and in-jokes, resulting in a lot of people wondering just who on earth this "Sans" or "Toriel" is, or why "Genocide route" was being thrown around so much. See also Hype Backlash and Hype Aversion.
  • Fanon:
    • The skeletons in particular invite a ton of this:
      • Sans calling Papyrus by the affectionate nickname "Pap" or "Paps".
      • As a stylistic choice, many fan artists depict Sans as literally being chubby, in-spite of his being a skeleton. Which led to the popular fanon that both he and Papyrus both have some "Ghost Flesh" or other magic organs of sorts that they can manifest at will.
      • Papyrus is often associated with the color red or orange while Sans is associated with blue, presumably because that's the color of their outfits. This leads to things like Papyrus's magical abilities being depicted as orange in contrast with Sans's blue (even though both brothers use the same blue and teal colors for their abilities), and drawings with anything non-skeletal on their bodies (blushing, body fluids, the aforementioned "ghost flesh", etc.) being in these colors as well, even though Papyrus visibly has a normal pink-colored blush during his date , and Sans probably bleeds red, assuming it's not actually ketchup).
      • Sans's sprites have a pair of curved lines just under his eyesockets; what these are are never specified, but fandom tends to agree that they're bags or dark circles.
      • Sans's mouth is usually portrayed more expressively within fanart than it is within the official game. While the game usually portrays him with a jovial or sinister grin (only tweaking it slightly under certain conditions as to not make it seem jovial), fanarts tend to change the shape of said grin to make it more obvious he's not feeling happy at the moment, if they don't remove it altogether. Likewise, many people depict Sans as rarely opening his mouth while speaking, presumably because he's one of the few characters in-game who doesn't animate while talking (a few others being Undyne under certain situations and Alphys under most situations).
      • Sans's Offscreen Teleportation are universally called "Shortcuts", based on several lines of dialogue where he says he knows a shortcut immediately before walking you away from the destination or towards a dead end, but arriving at the same place anyway; he never openly associates them as the same thing, and there's no indication he's using his teleportation or actually meaning a shortcut at face value.
      • It is very, very common to depict Sans keeping/wearing Papyrus' red scarf as a Tragic Keepsake during a genocide route, to the point where it's pretty much a shorthand way for fanartists to tell the viewer "this is Sans in a genocide route". Such a connection is never even hinted at in-game. As an aside, this is usually complimented by Papyrus keeping/wearing Sans's jacket in fanart related to the aforementioned hypothetical Genocide route where Sans is killed first instead.
      • It's very popular to depict Sans's hoodie with fluffy or furry lining on the hood, despite official artwork and merchandise showing that's not the case.
      • Sans's Glowing Eye of Doom during the final battle of the genocide route has inspired some creativity in the fandom. In the game, it only starts glowing when he's using any of his Mind over Matter attacks on you, but some fans depict it acting up whenever he's using any kind of attack (likely for dramatic/symbolic effect) or feeling particularly strong negative emotions, which somewhat conflicts with the in-game implication that his eyes turn black to indicate this. Fans have also taken liberties regarding what the glowy-stuff actually looks like; because of the game's simple sprite design, it only appears to be a flashing blue iris and nothing more, but many fans draw it being flame or neon-like, often trailing or flaring out of his eye.
      • When Sans is defeated after his boss battle, something red starts to come out of him. Opinions vary widely as to just what this is: the most obvious answer would be blood, but monsters are explicitly stated to turn to dust after they die, so this is unlikely. Other common interpretations include ketchup, which Sans is shown to enjoy drinking on other routes, and raw Determination.
      • Fans really seem to like the idea of W.D. Gaster being Papyrus' and Sans's father. They do likely have some connection, Sans uses "Gaster Blasters" in an attack, for example, but whatever it is, the game doesn't elaborate on it.
      • A popular fanon origin story for Sans and Papyrus is that they're creations of Gaster's, typically his clones. Some play this for drama, with Gaster performing horrible experiments on the brothers, while others go for a lighter take and simply characterize Gaster as an eccentric scientist who wanted children, or a scientist that got attached when an experiment produced unintended results.
      • Fans seem to have unanimously agreed that the mysterious entity found in the Dummied Out Room 269 (the entity in question is identified as spr_mysteryman by the game's code) is W.D. Gaster. This is not confirmed, but you wouldn't know that going by the fandom - even the Undertale Wiki goes with it. In the same vein, for all the different ways fans have chosen to design Gaster for their fanart, it's also just about unanimously agreed that he has a circular hole through the center of each of his hands. The ambiguous way his sprite is designed could be interpreted this way, but you'd be extremely hard pressed to find one artist that doesn't.
      • Sometimes, the Gaster Blasters are portrayed as the "pets" of Sans and Papyrus. They can be surprisingly cute for floating snake heads that shoot giant laser beams.
      • Papyrus's Voice Grunting noises are nondescript compared to Sans's, but he is frequently interpreted as sounding like Skeletor. Similarly, Sans's voice has been interpreted as sounding identical to Cr1TiKaL so often that he pointed it out in his video playing the game, saying that he had gotten a ton of messages and emails telling him about how well his voice would fit. Fan voice actors took the idea, ran with it, and gave the fanon voices a sort of Vocal Evolution where they're not straight impressions of the source voices, but still have the qualities of them, with Papyrus being higher pitched with a tendency to roll his r's, and Sans having a low, drawling voice.
      • A popular joke/plot point in fan material is Sans having a ridiculously high tab at Grillby's that he never pays off, so much so that "pay your [optional expletive] tab" is practically Grillby's fanon catchphrase. Although we do see him put a meal on his tab at one point in the game, we're not given any definite evidence that he does this regularly, and the notion that he does actually conflicts with the bird monster's statement that Sans is one of Grillby's best customers (Of course, said bird monster later admits that he's making everything he says up, so that doesn't really mean much).
      • Fans often agree that Papyrus has access to the Gaster Blaster attack. There's not much to indicate he does other than his "non-bone attack." However new dialogue from the 1.001 update supports this a touch: After abandoning a Genocide route at Papyrus, in his room is the box of unused bones. When examined:
      Papyrus: HAD I ONLY USED MY SPECIAL ATTACK, YOU SURELY WOULD HAVE BEEN BLASTED TO... WAIT, WHERE'S MY SPECIAL ATTACK?
      • Related to above, a common theory is that Papyrus is as powerful or even stronger than Genocide Sans but is Willfully Weak because of his kind nature.
      • Since, when killed on a Genocide run, Papyrus's head falls off and dissolves much later than the rest of his body, it's a common theme in animations to depict Frisk/Chara stepping on his head to finish him off.
    • As a popular stylistic choice, fan art of battles will almost always show a human's soul being represented as a heart floating a short distance in front of or inside of them. This is mostly to help such art make sense, as otherwise a full combat floating heart looks awkward at best.
    • A lot of people interpret the protagonist as being completely mute or unable to talk. This doesn't make a lot of sense because that would render them unable to talk to people on the phone, but regardless the idea persists. A common variant of this is to interpret them as being mute by choice. They are often presented as being fully capable of speech, but preferring to communicate with sign language. A possible explanation for why this is popular is simply that ambiguity is such an integral part of the protagonist (to the point that calling Frisk "he" or "she" is enough to start a flame war) that even assigning a certain voice to them just doesn't seem right.
    • There have been quite a few works which portray the six other human souls as children just like the protagonist and the Fallen Child, even though the game doesn't provide any concrete indication as to any of their ages. There is evidence this could be correct, however; Toriel's house does have toys and kids' shoes of various sizes, which supports the theory, and Toby also referred to several children falling into the monsters' realm in an interview before the game came out.
    • We never do see what Napstablook's cousin looked like before becoming Mettaton, but most fanart depicts them as a little pink ghost with long hair covering one of their eyes, much like Mettaton EX. Likewise, the Mad Dummy's ghost is assumed to be yellow or orange like them, and the Ruins Dummy is assumed to be a green ghost with a missing eye.
    • Similarily, we never do learn Napstablook's cousin's name before he became Mettaton. A large majority has settled on their name being "Happstablook" due to Papyrus dubbing them as such. Note (spoilers) 
    • In the fandom, The Fallen Child is almost universally drawn with red eyes, this might be because of the Soulless Pacifist Ending, where they pull an Eye Awaken with glowing red eyes. This is done regardless of whether Chara is being portrayed as evil or not.
    • Similarly, in contrast to the protagonist's gender which is often left completely open-ended, fandom does tend a little toward interpreting Chara/the Fallen as female. A few factors in this are the rosy cheeks on Chara's sprite (which can be gender-neutral but are often associated with femininity) and the very name "Chara" being indicated as the proper name for the Fallen and vowel-ending names in English, the game's native language, usually being feminine (on top of "χαρά", in Greek, usually being feminine when used as a name, meaning "joy", "beloved", or "delight"). There is still tons of room for a male Chara in fandom, though, especially given Toby Fox's indication that you should use your own name for the Fallen (if you can't think of anything else), suggesting that the Fallen's gender should perhaps match the player's own.
    • The First Child's real name being Chara. Officially they have no canon name for the reasons given above, but the game has a special response if you use it, the launch trailer using the name, and the in-game files refer to the character as such, causing many to consider it as good as canon at this point.
    • In some lighter hearted stories with The Fallen child/Chara and Frisk (either be it share mind or somehow separate), They're generally shown as sociopathic in words alone, being harmless.
    • Chara is very commonly depicted in fanworks as a victim of prolonged abuse while they were alive and before they fell into the underground by those who don't believe they are evil and want to tie their unspecified "not happy reasons" for climbing Mt. Ebott to their hatred of humanity. Adding to this, and connecting it to the above headcanon that their eyes are red, their eye color is often portrayed by defenders as one of the things the humans in the surface abused them for, like here. Frisk is also very commonly believed to have red eyes, and occasionally to have been a victim of abuse like Chara, leading them to climb the mountain just like them.
    • Despite Napstablook's overworld sprite depicting them as taller than Frisk, Sans, and quite a number of other characters, fanart will frequently depict them being the size of a plushie.
    • The six previous humans have varying thoughts on what they should act like, but the Dark Blue/Indigo SOUL is generally portrayed as being extremely violent, verging on No Mercy run levels of murderous due to their lost possessions, which are said to be covered in dust, which people frequently take to specifically mean the corpses of one or more monsters.
    • Fan depictions of Mettaton often portray him as someone who Really Gets Around and hits on Anything That Moves. While he's a vain Mr. Fanservice who banks a lot of his popularity on his good looks, the game never makes any indication of his sexual or romantic inclinations, even in Getting Crap Past the Radar form.
    • Mettaton is not exactly the greatest boss to Burgerpants, but a sizable portion of the fandom likes to portray him with an "I will bully you- but if anyone else bullies you, they get hit" mentality.
    • Burgerpants, to many fans, seems to usually be depicted with a slight Southern US/Texas drawl, and usually smoking a cigarette, sometimes to the point of chain-smoking (despite only one of his expressions featuring a cigarette).
    • Despite her very modest sprites in-game, most artwork and fictional descriptions of Toriel depict her as having a very full, voluptuous figure, typically sporting very large breasts and wide hips. While this is no doubt a result of the common sexualization of fictional characters, it's also likely the result of Toriel's motherly nature, as full-figured or voluptuous figures are commonly associated with matronly archetypes.
    • It's not uncommon to see fans depicting the flame girl in a Sailor Fuku (who is sometimes simply called "Fuku") as either Grillby's daughter or at the very least related to him somehow.
    • Virtually everything about the nature of the Fallen Child's purpose in-game.
      • One of the most popular theories, by far is that the Fallen Child is the one who begins moving Frisk during the cutscenes in the Genocide Route.
      • Another big idea that's risen recently is that The Fallen Child is the narrator in all routes, not just Genocide.
      • In addition, in part because of their name in promotional materials which is derived from "character" and "True Chara" in the game's files, it's been speculated that Chara is the actual player character, and is either controlling Frisk throughout the game or sharing control with them as they did with Asriel. Suffice to say that the Fallen Child is one of the most important and most poorly understood characters in Undertale, and that speculation about their role is unlikely to reach a conclusion at any point in the near future.
    • Pretty much any full-body depiction of the shopkeepers (with the exception of Gerson, whose full body is seen on his tarot card,) since their sprites are only seen from the waist up.
    • A pretty popular "after the Golden Ending credits" theory is the idea that Frisk came back and retrieved Flowey in the underground, with the determination of including him in their new family in the hope of eventually redeeming him. Cue Flowey learning (though always perplexed and unwilling) from all the main characters.
    • As mentioned with Chara aka The Fallen Child example above, Frisk's gender is intentionally written to be up to the player's interpretation, never explicitly referred to as male or female, but the fanart of them as a teen/young adult tends to lean more on the latter (Albeit slightly).
    • Asriel almost in his entirety ends up being this, as a result of being a One-Scene Wonder. From the little we see of him, we know he's generally lovable, innocent, and childlike, though acceptably adult considering all he's been through over his existence. On the other hand, (perhaps purely to emphasize Chara's mean-spirited nature from artists who believe in that interpretation), a lot of fanart tends to depict him as an incredibly cowardly, naive crybaby prone to fleeing, hiding, or crying at the first sign of conflict, not unlike Lucas at the start of MOTHER 3. Granted, much of this particular fanart is set before Asriel and Chara's collective deaths, though from what we hear ingame, Asriel was surprisingly adult even during those years and was reluctant at worst when facing hard situations. When this isn't the case, Asriel as a child is usually at the very least depicted as far more naive and gullible than is implied ingame. As a saving grace, much if not all of these cases tend to be for the sake of emphasizing Asriel being adorable rather than putting him down in any way.
  • Fan-Preferred Couple:
    • Outside of Canon pairings, Mettaton/Napstablook enjoyed popularity for a while, although its popularity dropped significantly after Mettaton/Papyrus became big and Napstablook and Mettaton being cousins became a more well-known fact.
    • People seem to ship Toriel/Sans a lot due to their Odd Friendship as shown from the true end, as well as Toriel being shown to be very angry at Asgore. On the other hand, people do also ship Toriel/Asgore.
    • Mettaton/Papyrus is huge, mostly based on Papyrus' comment about Mettaton and his sexy rectangular body.
    • Frisk/Asriel is incredibly popular, given their interactions at the end of the True Pacifist route.
    • Chara/Frisk has been growing pretty fast recently, possibly because they're the only humans in the game.
  • Foe Yay Shipping:
    • The player character has the option to flirt with quite a few of the enemies in the game, though they obviously don't remain enemies for long regardless if you spare or kill them.
    • Chara x Sans is also very popular, coming on the heels of the final Genocide route battle and the preexisting popularity of Self-Insert Fic shipping with Sans, which Chara's metatextual nature plays well into.
  • Friendly Fandoms:
    • With the JoJos Bizarre Adventure fandom, due to Mettaton EX's rapid posing and the Dummy's penchant for throwing knives being reminiscent of DIO. Some people have also compared Asriel and the Fallen Child to a younger Jonathan and Dio Brando.
    • Most of the OFF fandom as well, due to similar aspects through the games, like graphics, wacky monsters, a mostly Featureless Protagonist, and a shockingly dark storyline and having to face the consequences of killing everything in your path.
    • For the same reasons as the OFF fandom, EarthBound and MOTHER 3. It helps that Toby Fox had previously contributed to the community. There's a lot of crossovers in their ranks, usually under the name "Mothertale."
    • Fans of Wander over Yonder have developed an interest in the game for having similarities with the show, like both having characters who are skeletons, wacky monsters, and for having a similar goal of befriending the enemy instead of defeating them, resulting in a fair number of crossover fanart like characters of both cosplaying as one another.

    • Fans of Steven Universe seem to enjoy Undertale a lot. Tons of crossover art of the two, including fusions and depictions of the characters together or in each other's setting, has been created, and the fandoms tend to get along very well ("Stronger Than You", as mentioned above, nonwithstanding).
    • The Touhou fanbase has also latched onto Undertale due to Toby Fox being a fan of Touhou, The Bullet Hell segments in Undertale being inspired by Touhou, references to the games, and Toby even using ZUN's musical style on a few songs (most notably in "Battle Against a True Hero".
    • Homestuck fans, former or otherwise, make up a large portion of the Undertale fanbase due to having similar (albeit more lighthearted) humor, the same musical inventiveness of Toby Fox, timeline shenanigans in the plot, and three dimensional characters that seem simple at first glance.
    • Fans of Spec Ops: The Line have been warm to Undertale, as both games heavily deconstruct the idea of the player killing everything in sight to horrific extents.
    • As result of various shoutouts and similar messages, fans of Yandere Simulator and Undertale get along quite well. It also helps that YandereDev himself seems to be a fan of Undertale.
  • "Funny Aneurysm" Moment:
    • For Black Comedy, Flowey tricking the player into catching all the "friendliness pellets" and making it clear that "In this world it's kill or be killed". In a Genocide Run, his "best friend" the Fallen kills him so that he faces Cessation of Existence.
    • Flowey makes a surprised squeak when Toriel bats him away in the game's beginning. She also calls him a terrible creature for tormenting a child, that is, you. Then you learn that Flowey is the soulless incarnation of her son Asriel, which means Toriel hurt her own child and didn't know.
    • Similar to the above, Flowey also calls Toriel an "old hag" if you kill her, and refers to Asgore as an "old fool" if Flowey performs the coup de grace on Asgore on the Neutral path. His contempt for those two becomes depressing and disturbing after you realize that they're his parents.
    • Dr. Alphys's Establishing Character Moment appears to be an adorkable scientist who accidentally created a "killer robot" that loves a good show. Then you learn that the "killer robot" was a charade she made up to as to insert herself into your story, and she performs one Epic Fail in putting on a show to "save" you. Furthermore, you may learn that she was suicidal and does kill herself in several endings. In a True Pacifist Run, you learn that part of her baggage comes from creating the Amalgamates while attempting to save monsters.
    • Mettaton at one point dresses up as Juliet and sings that the human and they are Star-Crossed Lovers and that "it breaks my heart" to Shoo the Dog. Later on Mettaton reveals before his boss battle that he actually likes humans a lot, admires them, and holds no grudge. In a Genocide Run he tries to fight you to save the humans.

    G-H 
  • Gateway Series: To Bullet Hell games.
  • Germans Love David Hasselhoff: Undertale is very popular among Korean and Japanese gamers. The Korean translation of the demo, the only current official translation in a language other than English, was made in response to fan request, with a fan translation of the full game in Korean coming out soon after its release. The fanbase in Japan is also quite large and probably more unified there, with some big names among the fans including Yoko Taro, Swery 65, and Hato Moa. It also received detailed entries in Pixiv dictionary. This culminated in a much-requested Japanese localization announced in E3 2017.
  • Goddamned Bats: In the demo, Vegetoids. No ACT will placate them; the only way to spare them is to carefully whittle their HP down until they're willing to give up, which risks accidentally killing them. Additionally, the "Eat" act kills them. This is both obnoxious and wildly out of place — in both the rest of the demo and the entire full game, every monster can be placated without having to Do Well, but Not Perfect at reducing their HP, and no ACT will ever kill a monster. Thankfully, both of these traits were removed from Vegetoid in the full game.
  • Good Bad Bugs:
    • The save file is in no way protected from editing. The very first line is your character's name, in plain text. And unlike when entering your name at the beginning, printing your name during the game has no character limit.
    • You can encounter a bug if you stand on the farthest of either side of the path before Undyne's speech. Depending on which side you're on, you can either get a head start as you go through the cave before initiating the first fight, or immediately start the fight outside of the path and be unable to make progress without restarting as you're constantly chased. Also, the boss constantly respawns at the spot where they land, even if you run away repeatedly.
    • A common "glitch" in games created with Game Maker which is also present in Undertale: walking up against a wall and holding both the up and down arrow keys will cause the Human Child to walk in both directions at once, e.g. walk up for one frame, down for one frame and then repeat, creating a flickering affect as they stand in place against the wall. Similarly, holding down an arrow key and keeping it depressed while switching to another window will trick the game into thinking you're still holding the key down, making you walk in place. Despite looking rather silly, both these techniques are considered beneficial, can be combined together so you can do something else while waiting for monsters to show up, and are commonly used in the No Mercy run due to the encounter rate being determined not by time, but by the amount of steps you've taken. This bug has been dubbed the "Murder Dance" by fans.
    • If you call Papyrus or Undyne while standing on the conveyor belt in Alphys's room, Frisk will keep moving and the dialogue for the person you called will scroll off screen. Coincidentally, the call dialogue for this room is likely to be some form of "Don't do that!", causing many players to think it was a deliberate Easter Egg until it was fixed in the patch.note 
  • Harsher in Hindsight:
    • During the judgment in a pacifist run, Sans says he would have given up a long time ago if he were in your position. This seems like his old laziness/apathy acting up, but in the final battle, as a lost soul he says things like "just give up. i did." and "why even try?" Everyone else as seems to revert to how they were before you got to know them, but Sans was never explicitly despondent up to this point. To say nothing of the Kill 'em All run where he says that he can't bring himself to put any effort forth, because he knows that everything is going to reset anyway.
    • In the Golden Ending, Asriel says that he will become a flower again after he releases everyone's souls and pretty much tells you to leave him alone in the Underground and not reset so that everyone else can have their happy ending. On Undertale's first anniversary, Toby on Tumblr created a canon Q & A with all the characters being asked about Papyrus's favorite food. Asriel has reverted to Flowey form, though he does answer the question correctly and doesn't try to kill you or criticize the questioner.
  • Hilarious in Hindsight:
    • It's hard to tell if it's this or if he knew note  but Toby asking for NSFW images of the game to be tagged "Undertail" so people browsing the game's name wouldn't see stuff they didn't want to was given kind of a humorous spin when the Furry Fandom completely embraced the game. Likewise a line from Sans in Hotland. It Makes Sense in Context as he's selling hot dogs, hot cats, and other such things, but it also sounds like a tongue-in-cheek reference to the inevitable Furry Fandom.
    Sans: ... you really like hot animals, don't you?
    • Within the game itself, there's Papyrus' line during his "date" when you examine the computer where he claims to be extremely popular on the internet. It was meant to be a joke about him being kind of a loser and won't accept it because of his ego, but in the actual internet, well, even he would be stunned by how popular he actually became. Likewise, the conclusion of his date has him lamenting that he's drawn the player into falling desperately in love with him. It's supposed to be a jab at his ego, but ironically he's considered a Mr. Fanservice with a thriving fangirl following in real life, complete with Self-Insert Fic and art. On a somewhat lighter note, during the fight against him, he will note several things that he imagines will happen should he capture you and join the Royal Guard, including Asgore making hedge trim art in the likeness of his face. He actually gets this wish granted in the True Pacifist ending, despite the Royal Guard being disbanded before he can become a member, as Asgore can be seen making said hedge a reality in front of Toriel's school on the surface.
    • Whether or not Toby knew or heard about it beforehand, real-life Glamburgers have existed for over a year, although they're infinitely more expensive and aren't purple, as seen here.
    • After the True Pacifist ending, talking with Mettaton will trigger some dialogue, and among those, talk about having Toriel plushies, but with his face on them. Then a wish was becoming true.
    • A cross-game moment, but Bravely Second, which came out in Japan just a few months before this one, also uses Breaking the Fourth Wall to call out the player for messing with the game's characters for their own sick amusement, and has a Final Boss that addresses the player, messes with your save files and can attack while you're on the menu screen. However in that game, it undergoes a Decon-Recon Switch almost immediately.
    • Another cross-game thing; many people have noticed similarities between Mettaton and securitrons note . Likewise, it's a common joke to swap Photoshop Flowey's face for Yes Man's.
    • In the Monster Rancher episode, "Holly's Happy Birthday", Suezeo and Hare (both males) both leap at each other for a kiss gone wrong after being influenced by an outside source (Mocchi putting a flower crown on Holly before kissing her). Undyne and Alphys (both females) also attempt this after being influenced by an outside source in the True Pacifist ending (Mettaton encouraging them to just kiss already) before being stopped by Toriel. Although Undyne does kiss Alphys in the credits.
      • What makes this moment funnier is that when Mocchi does kiss Holly (on the cheek), all the other monsters freak out. This game allows you to flirt with slime and your own surrogate Goatmon, and date a skeleton with an Awesome Ego, a crazy lesbian fish lady, and a geeky lizard scientist (with a potential option in the latter to kiss her as part of the roleplay), all without nobody batting an eye (Well, except Toriel, who questions it if you do flirt with her, and calls you 'interesting' if you do this after calling her 'mom', even telling Sans about this in the True Pacifist ending, and Undyne in the Alyphs date.)
    • Undertale and Steven Universe are Friendly Fandoms because they both feature an All-Loving Hero who is a Technical Pacifist. One Steven Universe episode titled Onion Gang has an expy of Frisk named Soup and a question of sparing or killing an innocent creature. (As a bonus, this episode was released on Undertale's anniversary.)
    • After Papyrus has an admitted obsession with making spaghetti, which is often inedible, it's hilarious when in a Q & A that Toby created he admits that he's never tried spaghetti and only makes it because everyone else seems to like it.
    • W. D. Gaster bears a striking resemblance to this artwork of SCP-1599.
    • By chance, Papyrus is remarkably similar in attitude to Horrorman, a cheerful skeleton from the long-running Japanese kids' franchise Anpanman. The only real difference is that Horrorman is technically a villain, but they're both too goofy and good-natured to be effective at their jobs. They also both enjoy being nice to other people.
  • "Holy Shit!" Quotient: The fight with the Final Boss of No Mercy route is this, especially the Alpha Strike. The reaction of everyone playing the game blind against this boss can be boiled down into "WHOAHWHATTHEFUCKISTHATSHITFORREAL".
  • Hype Aversion:
    • While Undertale is a great experience, the fandom overpraises it too much sometimes, with many people saying it's "THE BEST GAME EVER! 20/10 " or "LITERALLY MADE ME CRY FOR HOURS!", and they are also very prone to reveal spoilers (especially Tumblr). Some people would rather not play the game at all just to avoid the risk of disappointment.
    • As mentioned under Hype Backlash, the fact that the game has to be played blind for the full experience is a huge mark against it for a lot of people wary about the game for one reason or another, since most responses to "Why should I give this game a chance?" can be summed up in "You just have to take my word for it because everything I could praise about it is a spoiler."
    • Winning GameFAQs "Best. Game. Ever." poll over well-established favorites like The Legend of Zelda: Ocarina of Time and Final Fantasy VII left many people writing it off as yet another case of an Internet fandom going overboard with its hyperbole, or even refusing to play the game purely out of spite.
  • Hype Backlash:
    • Not as fierce as others, but still inevitable with a game that received such a storm of popularity and critical acclaim. Putting aside people who hate it simply for being popular, the most common criticism from players is that the story is good, but the bullet hell mechanics often turn people away. There's also many who don't agree with the way the message is handled in the No Mercy route, with the primary complaint being the game permanently locking you out of the Golden Ending in all future playthroughs is overly harsh. Another portion of this is that every single reviewer for the game recommended playing it first, and many agree that the best way to play the game is almost entirely blind, or completely blind, which becomes a problem due to the advent of message boards and Youtube.
    • While most fandoms tend to spread quotes, images and references to their fandom on things that have nothing to do with it, the Undertale fandom is currently one of the most persistent, causing quite a lot of backlash from people that are by now annoyed of all the "X is filling you with Determination" memes, comparing random characters (sometimes even of older series or games) to Undertale characters and similar.
    • This is especially true for Let's Players and streamers, who always come under fire from their Unpleasable Fanbase, some of whom think they should take a certain route, and others who feel they should play the game blind. It's made some of them refuse to Let's Play the game at all. Those that DO play the game seem to regret it later since no matter what they do, it's never good enough. Most start playing blind, but if they don't follow the pacifist route on the first time or miss a small detail, then they're "playing the game wrong". The most common case is when the Let's Player doesn't know how to spare Toriel, so they kill her, and the entire comment section is filled with angry comments demanding the player to start the game over and "do it right this time". If the LP'er does reset, they get further angry comments calling them a "sissy".
      • Let's Players that have proclaimed to play all variants often get yelled at for playing "in the wrong order". While half the fandom thinks that one needs to play No Mercy and Neutral first to really enjoy the perfect ending, others call the player stupid because by doing that they would just not get to see the charm of the game and lose interest.
      • One of the biggest cases regarding a Let's Player clashing with the Undertale fandom is apparently Mangaminx. She got pretty much the whole game spoiled in the comments on her first video despite her explaining extensively in the video and description that she wanted to play blind. She then proceeded to kill every character she could out of pure spite (with missing a few where she was too slow such as Mettaton), only to now amuse herself with videos where she ridicules the comments she gets on both her Undertale videos and her ridicule-videos. Her placing it on the top of her "TOP5 most disappointing games 2015" more or less made her a proclaimed enemy of the entire ''Undertale'' fandom.
      • Markiplier had an equally controversial first run on the game, as when he got to his second video, people slammed him for not using the accepted fanon voices, going so far as to give him, his mother, and his dog death threats. This convinced him to stop playing the game for over a year, only to return in October 2016, but without listening to the fans.
    • Within the fandom itself, the track "Megalovania", used for the No Mercy Final Boss fight. Some fans have formed the opinion that while it's a great track, its sheer popularity dwarfs that of most other tracks in the game that don't get as much as love as they feel they deserve.

    I-P 
  • Idiosyncratic Ship Naming: "Fishbones" for Papyrus/Undyne, "Kingdings" for Asgore/Gaster, and "Fontcest" for Sans/Papyrus.
  • It's Easy, so It Sucks: Some people think Undertale is a bit too easy on the Neutral and Pacifist routes. While the fact that you only have 20 HP on the latter makes things harder, some fights only amount to waiting out the enemy or performing relatively simple sequences of ACT commands, so there's less strategy involved in going on the offensive, and in the final boss on the latter route, you're automatically revived if you die. The Genocide route has two of the hardest bosses in the game, especially the final boss, but as you can see elsewhere on this page, there are reasons why a lot of people don't want to play it.
  • It's Popular, Now It Sucks:
    • As mentioned above, ever since Undertale began winning brackets in the 2015 GameFAQs "Best. Game. Ever." contest, it brought complete ire to many people as it beat Super Mario World and several other games that are considered Sacred Cows.
      • One of the follow-up polls had GameFAQs ask users if they were planning to buy Undertale since it won. The "No, and I refuse to ever buy it purely out of spite" choice came in second place with 24.71%.
    • Sans, being by far the game's most popular and well-known character, has had some people turn on him because of this trope, due to his seeming ubiquity and being a source of Hype Backlash. It doesn't help that you need to see or play the Genocide Run, which the game and a good section of the fanbase dissuades you from doing, to understand his popularity.
  • It Was His Sled: Many things from this game qualify due to the nature of it, but most particularly, the fact that there's even Routes in the first place. The game intends for you to play it through normally, then strive for one route or another to see what can happen within the game's parameters, but due to liberal discussion about routes and the many details of the storyline, most people introduced late to the game already know to probably play the Pacifist Route first.
  • Jerkass Woobie: Once one learns exactly why he is such a jerk in the first place, it's easy to feel sympathy for Flowey.
  • Just Here for Godzilla:
    • A prominent subset of the Undertale fandom is centered on Sans and the many AU versions of him, with little interest in the rest of Undertale. It's gotten to the point that many Sans fans view themselves as separate from those of the actual game or its other characters.
    • More specifically, a lot of people play the Genocide Route just to fight Sans, which is notorious for being the hardest fight of the whole game. Whether they reset after the fight is over and go for a Neutral ending or go all-out with the Genocide ending varies from player-to-player.
  • LGBT Fanbase: Undertale has a pretty decent one, with the prevalence of canonically LGBT characters note  and other characters appealing to the Bara Genre note .
  • Love to Hate:
    • Flowey. Everything he does is to spite you or make you suffer in some way. To the point where fans find it more endearing and less annoying. It helps that he is a Magnificent Bastard, killing Asgore and absorbing the six Souls in the Neutral path and leading a plan to obtain all the Monster Souls by convincing you to go for the Pacifist Route. This gets turned on its head however when it's revealed that Flowey is the reincarnation of Asriel Dreemurr who can no longer feel any positive emotions, which makes him sympathetic.
    • Jerry is disliked by just about everyone in-universe, and fans happily picked up on this.
  • Memetic Badass:
    • Sans, due to being the most powerful monster in the underground despite his laziness, and really showing it on the No Mercy path.
    • Undyne, a powerful, hammy, and relentless fighter who suplexes boulders because she can. She falls even more into this in the No Mercy run as Undyne the Undying, where she is the only boss that can take more than a couple hits from you; not even Sans can do that.
  • Memetic Loser:
  • Memetic Mutation: Lots, with this game's writing. Now has its own page.
  • Memetic Troll: Chara gets this reputation for their influence in the backstory, as well as the permanent effects they have on the game after a Genocide run is complete. While Flowey and Sans are canonical trolls, Chara undergoes Alternate Character Interpretation as a smartass that casually does mean things (usually to the Human Child or the Dreemurs) just because they can. Chara's Deadpan Snarker tendencies also tend to crop up in narration as teasing jabs at Frisk. There's even a theory that Chara doesn't actually kill the monsters during the corrupted Pacifist Ending, but is messing with the player and letting them assume the worst to teach them a lesson about the consequences of their actions.
  • Misaimed Fandom:
    • Overlaps with Do Not Do This Cool Thing. Many fans of the game actually enjoy the No Mercy route, despite it having a goal of making players feel terrible and unsatisfied. These tend to be story-focused fans (the dark, tragic plot can be just as gripping as the normal story, and it shows many characters at their best) and Challenge Gamers (with the route hosting two extremely tough fights that require players to seriously master the game mechanics in order to succeed). It's worth noting that the majority of Sans's popularity comes from the No Mercy route.
    • On the other end of the spectrum, there are MANY fans who openly object to people not playing the True Pacifist route for their initial blind playthrough, which defeats the purpose of playing the game blind and making your own choices without knowing of the consequences.
    • Players scapegoating them for the No Mercy Run, and, depending on your interpretation of them, believing they're inherently evil in the first place. While Chara does become an Omnicidal Maniac at the end of the Genocide run and destroys the world (and the game), Chara is not responsible for every kill on the No Mercy Run - the player is. Chara is able to take over because the player's LOVE is transferred to them, and it could be that that drives Chara into believing Genocide is the best and only thing left to try. In other words, Chara's behaviour is very likely affected by the player's actions, and there is evidence to the idea that they were at least a good person who made bad mistakes in the Pacifist run, just like the other characters.
  • Moe:
    • Asriel Dreemurr is this to many, many fans of the game, thanks to his adorable design, sweet personality, gentle little voice, and status as a Grade-A woobie.
    • The entire Dreemurr family could be this. Toriel is loved by many for being so loving and caring to the player, and for being one of the sweetest, and most polite characters in the game. Her ex-husband, Asgore, is also adored by a good chunk of the fanbase, and he's just as sweet and polite as his ex-wife. All three are also huge woobies.
    • Just about every major character, and even some minor characters, qualify to some extent. Frisk on a pacifist route is a sweet little kid, the Dreemurrs are mentioned, Napstablook is a adorable ghost monster with almost no self-esteem, Sans is a chubby grinning skeleton who masks his inner frustrations with jokes, Papyrus is a dork, Undyne is a Defrosting Ice Queen tsundere, Muffet is an incredibly cute spider-girl who loves baking and tea parties, Alphys is an emotionally-vulnerable adorkable anime nerd... There's a reason even people who haven't played the game love the characters.
  • Moral Event Horizon:
    • In the Fallen Child's backstory, the Thanatos Gambit of eating buttercups knowing it would poison the Fallen, possessing Asriel, and forcing him to be Mistaken for Murderer by humans in hopes of either restarting the war between monsters and humans or, in a lighter approach, saving all monsters.
    • For Toriel, Asgore crossed it by declaring that any human that fell down into the Underground would be killed and their soul used to break the barrier and kill all humans. What's more, Asgore agrees with her. While he clearly is not remotely happy about what he's doing, he knows full well that his plan to harness the souls of seven dead children to exterminate the human race puts him beyond redemption, and as a result he doesn't allow for any scenario in which he both fails his mission and continues to live. He refuses to let the child spare him, going so far as to smash the mercy button off of the player's command menu, and when the child wins and spares him anyway, if it's a second playthrough and Flowey doesn't show up to kill him, he kills himself because he simply can't live with having taken six children's lives.
    • By the end of the No Mercy run, the Fallen Child has almost taken full control of Frisk. Why is this important? Because they know Flowey is actually their adopted brother who loved them dearly... and they, not Frisk, kill him anyway.
    • The entire No Mercy run is a cavalcade of horrible, horrible actions the player commits, but the game always gives them an out, up until they go up against Mettaton NEO. Finishing off Mettaton NEO after killing every other monster in Hotland is the true "point of no return", and only resetting your save and starting over can get you off the genocide at that point. And actually finishing this merciless route is an even greater point-of-no-return from which no amount of resetting can truly redeem you.
    • There are a couple other important "turn-back" horizons: You can take Papyrus's offer of mercy, or you can spare the Monster Kid before the Undyne battle.
  • Most Annoying Sound:
    • Get used to the sound of your soul shattering into pieces followed by "Determination", especially if you're on a No Mercy run and find yourself against the two bosses that pose an actual threat.
    • The constant notification sound you get from Alphys's social media posts when you're trying to navigate Hotland can get quite grating, but then again, that's the whole point.
  • Narm:
    • Sans's warning that the player is "gonna have a bad time" during the Genocide route makes for an incredibly well-implemented Meaningful Echo near the end the game, to the point where the phrase is almost as ubiquitous with the character as the battle itself... except for anybody familiar with a certain outdated meme. The line isn't ruined, but it takes quite a bit more effort to take it seriously.
    • To some, the puns come off as this - mostly with the fact that some characters feel the need to bring them up when it seems like there are more important things.
    • On a No Mercy playthrough, most of the background music is slowed down drastically, becoming especially groaning and dirge-like when the player is about to commit a Moral Event Horizon of some kind. In most situations, this fits the atmosphere of the player indiscriminately slaughtering anything in their path... but it fails to make the Temmie themes any less goofy-sounding.
    • In the non-violent ending to the Mettaton EX fight, Mettaton gets a lot of viewers calling in to his show, and he realizes how much he means to them, before running out of battery life and powering down for the time being. It's a touching moment, but some players found it a little hard to take seriously due to the background music for this part being a remix of "Oh! One True Love", which had some pretty silly lyrics.
  • Narm Charm: Yeah, Photoshop Flowey may seem like something out of a stereotypical, low-quality creepypasta and Asriel's powered up boss form might look like an eight-year-old's Mary Sue OC complete with rainbow themed attacks, but it fits, since Asriel is about that age anyway, and seems like the kind of kid who would come up with such narmy material, and adds onto the bosses' cool factor. As the Draco in Leather Pants example shows, even his boss forms have their fans.
  • Nightmare Retardant:
    • A possibly deliberate example. The battle against the Endogeny Amalgamation. It's a big, faceless dog abomination... that's still just a playful dog in the end. The fact that the hilarious "Dogsong" starts playing when it's happy enough just seals the deal.
    • Seeing the Amalgamations at the end reunited with their loved ones and being accepted back into the community does a lot to negate their scariness. Once again, probably intentional, as none of them were really evil.
    • The amalgamation that looms over the protagonist while they sleep. While you lie there in the bed, an elongated abomination looms over you... and slowly begins to reach out towards the unsuspecting child with a long, creepy appendage, and then... it tucks you in and gives you a gentle pat on the head. On top of that, it looks like a giant sperm, which may have been accidental.
  • Older Than They Think:
  • One-Scene Wonder:
    • Muffet the spider girl only appears for a single boss encounter, but she's gained a very large following.
    • Catty and Bratty, despite being easily missed shopkeepers with little relevance to the story, have a decent following. Their uniquely appealing designs and personalities help. Same goes for Burgerpants, considered one of the funniest NPCs in the game even though he's very minor.
    • Royal Guards 01 and 02 don't even have names and are only fought in a single encounter, yet they are found endearing by people who love how their battle plays out (01 finally admitting his feelings to 02 to which 02 reciprocates, the two sharing a very Bara Genre romance/bromance).
    • Asriel-as-himself (he himself considers him to be a different person from Flowey) is very important to the backstory, but only shows up in person for the final boss and what follows, after he leaves, he drops from the plot entirely unless you actively go to seek him out. Nonetheless, he has a disproportionate amount of popularity due to his tragic story, his adorableness, and the fact there's no happy ending for him.
    • Mettaton EX only shows up for a single battle, but he and his battle are so memorable that in many instances, the popularity of his EX form vastly overshadows that of his regular form. His Mettaton NEO form is also fairly popular due to how badass it looks, yet the sole scene it appears in is a boss battle where he dies in one hit and doesn't attack at all.
    • The only time you ever encounter the Fallen Child is after beating the Genocide Route, but man, are you in for something: pure Nightmare Fuel combined with calling you out for finishing the Genocide Route, topped off with them destroying the game and asking you for your soul to play again. If you thought you were the most dangerous thing in the Genocide route, think again!
  • Paranoia Fuel:
    • After your first encounter with Flowey in the demo, you know he vandalized the instruction manual. He also knows what you did during the game, and he'll leave more messages in the manual for you. He also knows you can save and reload. He even knows when you stick your nose where it isn't wanted, such as the website's source code. You can't hide from Flowey. Hee hee...
    • During the game, try to walk a screen or so into a room (such as the first save room), then walk back to the entrance. You might spot someone running back out of the room. Didn't we just say that you can't hide from Flowey?
    • From Sans's point of view, your ability to reset timelines is a major source of this. He may have gotten the happy ending that you worked so hard for...but that can all be taken away in an instant the moment you hit "True Reset". And a lot of players go on from that point to try out the No Mercy path out of curiosity.
  • Player Punch:
    • Toriel is not fighting to kill... yet you may very well end up killing her. This is especially easy to do on accident, because unlike many previous enemies, you can't spare her when her HP is low enough; attacking when her HP decreases enough will suddenly do way more damage than usual and kill her.
    • Let's say you kill Toriel, then reload your save to find a way to spare her. Flowey knows what happened the first time. Killing Toriel and then finishing the game otherwise peacefully will net you more than a few player punches. Not only do you learn that she and Sans had become friends and she had asked him to protect you, which was the only reason he didn't kill you on sight, but also that she was the former queen who lost both her children shortly after having adopted one of them. There's even one more where Asgore, anticipating his own death during your fight, will give some dialogue about how he wants to see his wife and child again. All of that together is just one big ouch.
    • Enjoy being an aloof completionist and seeing every possible route? Well, if you did figure out how to spare Toriel the first time, you'd have to go back and kill her to see what happens, won't you? After all, it's not like it's what you really want to happen, you just want to see everything. Nice try. Once again, Flowey knows what you did.
    • Applies even more strongly to the full game. The only way to replay the game after getting the No Mercy ending is to sell Frisk's soul. Have fun when, upon completing a True Pacifist run, the last shot shows that the Fallen Child has control over them and can ruin everything at a moment's notice!
    • If you kill Undyne on an otherwise mostly peaceful run, her death scene is one of the most tragic in the game. She attempts to continue fighting after her health is depleted, but her body is falling apart and it becomes a more difficult for her each turn, and her attacks slow to a crawl. In the end, she laments being unable to confess her feelings to Alphys, before starting to melt from trying to use DETERMINATION, and finally fading away, screaming her desperate refusal to die. All while a Lonely Piano Piece plays. The fact that Papyrus IMMEDIATELY calls you up to say that he thinks you guys should hang out some time and Alphys feels no need to watch the battle footage because she knows Undyne is too tough to ever lose a fight later on are incredibly harsh.
    • For those wanting to make Flowey pay for the suffering he causes, the game won't let you have any satisfaction if you choose to kill him at the end of a neutral run, as his last words are triumphant.
    Flowey: I knew you had it in you!
    • On a No Mercy path killing Flowey will give you even less satisfaction, because at that point he's scared shitless of you. His voice grunt and face changes to Asriel (who he actually is) as he begs you not to kill him. This very moment is the one where you have to push the action button to give the fallen child, Asriel's old friend, the last push needed to brutally butcher him with no further input from the player. You see him dying frame by frame.
    • If by chance a player wants to see a No Mercy run, but does not want to actually do one, they can opt to watch it via a Let's Play. Flowey says that these people are "sickos" who are too weak to do it themselves, so they choose to watch it.
    • Papyrus has a particular pained expression that only appears in especially depressing epilogues. Seeing him suddenly become genuinely distressed after spending the entire game so upbeat comes as a heavy shock to many a player.
    • At the end of No Mercy, Sans, at the halfway point of his boss fight, says he senses someone with a kind heart who wanted to do the right thing beneath the Omnicidal Maniac you and the fallen have become, and he's trying to get them to break free of the two of you. While it's implied he's bluffing (he does the same dialogue even if you haven't done a Pacifist run), it can easily ring true if you have finished one and you know Frisk's true nature. And the worst part is, unless you finally decide you can't handle it, Frisk is still stuck as the two of you's unwilling pawn as they kill the last three people important to them.
      • And if you at this point decide you can't go through with the Genocide anymore, Sans appears to offer you mercy, and you can use the Spare command on him. He seems to sympathize with your decision to throw away everything you've worked so hard on, and offers to console you...before killing you in an Unblockable Attack and suggests you don't continue this route. It's too late for forgiveness at this point. The only way you can redeem yourself now is to hit the Reset Button and set everything right...before you do something you'll regret.
    • Finished the No Mercy run and decide to go for a Pacifist run afterwards? Nope! Chara shows up at the last second of the ending to remind you that with Frisk's soul, they can possess the poor kid and undo everything Frisk worked hard for. Congrats, your desire for 100% Completion has ruined the game forever.
    • After you just barely manage to spare Asgore by lowering his health to 1, he's so moved by your determination to let him live that he decides to live underground with you & Toriel as a family. Then a familiar ring of "friendliness pellets" appears around Asgore and, unable to get up, he just sits there in horror while the bullets close in & kill him. Then one last bullet destroys his soul.
      • It's even worse if this is your second Neutral run. Instead of Flowey killing him, Asgore realizes how hopeless the wish to raise you with Toriel is, and notes that you have "the same feeling of hope in your eyes" as the original human child he adopted. Recalling how the prophecy said that that the one who would save them was someone from the surface, he comes to the conclusion that it was you, and commits suicide so you can take his soul and return, asking you to find a way to free them from above and saying your freedom is what Asriel would have wanted. And then Flowey destroys his soul anyway.
  • Portmanteau Couple Name: With the many memorable characters in the game, there's naturally quite a few, including:
    • Alphyne (Alphys/Undyne)
    • Papdyne or Undyrus (Papyrus/Undyne)
    • Soriel (Sans/Toriel)
    • Torigore or Torigorey (Toriel/Asgore)
    • Sansby (Sans/Grillby)
    • Papyton (Papyrus/Mettaton)
    • Charisk (Chara/Frisk)
    • Chasriel (Chara/Asriel)
    • Frisket (Frisk/Muffet)
    • Frans (Frisk/Sans)
    • Friskriel (Frisk/Asriel)
    • Flowisk (Flowey/Frisk)
  • Popular with Furries: The furry fandom loves Undertale, and not just for "Goat Mom" Toriel. They've even embraced the non-furry characters like Sans and Papyrus.
  • Praising Shows You Don't Watch: When considering for the prevalence and passion of the Undertale fandom, it's hard to make sense of how many fans have actually played the game. Given how the characters deeply overshadow the gameplay, this is understandable.

    R-Z 
  • Rescued from the Scrappy Heap: The months since the game's release have seen an increase in the use of the Comic Sans and Papyrus fonts, which before were two of the most hated fonts of the lot.
  • Ron the Death Eater:
    • Asgore is a frequent victim of this. While he did vow to take revenge on humankind for the death of his son and killed six humans to do it, he's clearly shown to regret doing the latter, and is so resistant to the former that he's so reluctant to act on the latter that he's willing to leave the monsters trapped Underground forever to stave off a war. However fanworks frequently portray him as abusive towards Toriel and driving her off with his bloodthirstiness, and AU versions often have him Take A Level In Jerkass. The chances of this happening skyrockets in works shipping Toriel with Sans, due to Die for Our Ship.
    • On the opposite spectrum, those who defend Asgore's actions make Toriel into this by making her looking like a crazy and emotionally abusive woman that can't let go and will give Asgore grief at every chance she can get all because Asgore's actions (or rather inaction) with the humans and keeping his people trapped in the underground. This is also despite the Golden Ending where Asgore wants to make amends and it shows him trimming hedges at Toriel's school, implying that the two of them might be working things out.
    • Alphys is definitely a flawed character, but portions of the fandom frequently exaggerate her negative traits by turning her into a full-blown manipulative Jerk Ass responsible for Gaster's death and abusive towards Mettaton and Sans whom it's implied she collaborates on research with. Even though she's shown to have a very strong conscience and dislike for actually hurting anyone.
    • As mentioned under Draco in Leather Pants, the Fallen Child may or may not be this. Their backstory is vague, and it's unknown whether they really wanted to free all monsters or destroy humanity, and to complicate matters further, there's a widely-growing chunk of the fanbase who believe the Fallen Child is really the narrator, and that they only become corrupt in the Genocide Route. If that really is the case, then all of the Axe-Crazy Omnicidal Maniac depictions of the Fallen Child fall under this.
    • Nothing in the game implies that W.D. Gaster was anything more than a good friend, or relative, of Sans's and a brilliant scientist who had an unfortunate accident, but the eerie nature of the Easter Eggs related to him have caused a lot of fans to portray him as a malicious figure bent on revenge at best, and an outright near-demonic entity at worst.
  • Sacred Cow: Downplayed and subverted in some cases. While the game is held up in very high regards from fans and even people who've never played it, it hasn't been immune to criticism. One of the biggest complaints among even fans is that you can't save Asriel.
  • The Scrappy: So Sorry, who is one of the game's only Bonus Bosses. Like Muffet, he was included as a backer's Kickstarter reward, but he has received significant hate for quite a few reasonsnote . Nearly any Youtube video of the fight with him is an explosion of disdain that leads to flame wars, and has noticeably more dislikes than other Undertale videos. The vitriol has even spread to the point where the backer has been harassed, requiring Toby himself to make a tweet asking them to stop.
  • Self-Fanservice:
    • While Undyne isn't terrible looking, fan-art often portrays her as a busty Amazonian Beauty (though the busty part is just as often forwent), when she's actually pretty scrawny and flat-chested.
    • Toriel falls victim to this as well. Toriel herself is absolutely adorable in game, but fan-art often draws her with curves (large hips/butt/bust; aka attributes normally associated with more fetishistic mother type characters) she doesn't have in-game.
    • Likewise, Asgore is not only cute, but very manly looking with his Badass Beard and has what is possibly Stout Strength. Fan-art of the character usually has him as either very muscular, very chunky, or both. Like with Toriel, it's a bit tough to determine what exactly his build is like under that armor and the pacifist ending that shows him wearing a pink shirt and blue pants, which entertains the possibility that he has a bit of heft on him, but not enough to fully determine that he is a heavyset guy.
    • Sans in-game is (usually) goofy and harmless, and while his laid-back attitude can be charming, fans sometimes portray him as more suave than he actually is. In addition, although the guy does indeed have a darker side to him, fans who are into that sort of thing often exaggerate it to a more standard case of Troubled, but Cute, sometimes giving him sharp teeth or other similar features. Many of the various AU versions of Sans exist for the sole purpose of this trope, or if they didn't start as Self-Fanservice to begin with, have otherwise been flanderized from their original concepts in order to make Sans more appealing to fans' given tastes.
    • To work with the fact that Sans and Papyrus are both skeletons, fanartists usually give them the ability to magically conjure colorful appendages and other organs for sexual pleasure, deriving from Sans's glowing blue eye in the No Mercy Run.
    • Mettaton EX is made a lot more feminine in fanart, having his legs, butt, and hips become larger and having his face made girlier. While in game he's still a Mr. Fanservice, he looks more akin to a glam rocker, ala David Bowie, than a woman.
    • Alphys also tends to attract fanart that downplays her hunchback or remove it entirely and have her teeth look normal (she has a fairly bad overbite). Even though these are small changes those two things can almost make her look entirely different.
    • Muffet is cute either way, but in-game she has some clearly non-human features: besides the obvious, she has a long thin neck, no nose, and stick limbs. A good deal of fan artists ignore this and draw her as a purple-skinned, but otherwise normal-looking girl with fangs, three extra eyes, and six arms.
    • The protagonist and the Fallen Child, despite explicitly being stated to be children, are often drawn in fanart to look like they're in their teens.
  • Ship Sinking: Toby sunk pretty much every ship that Sans launched when he tweeted that he's too apathetic and lazy for any kind of committed relationship.
  • Ships That Pass in the Night:
    • When you first fight Mettaton, one of his questions is "Would you smooch a ghost?" and all the answers are "Heck yes!" Thanks to that, Mettaton/Napstablook have a fair amount of followers on Tumblr. Some even draw Napstablook as a robot called "Napstabot", with a similar style to Mettaton. The real reason is probably that Mettaton was created by merging the soul of a ghost with a robot body, something not revealed in most endings. Ditto for why Napstablook's call-in in the bloodless conclusion to his boss battle starts to sway him. Of course, the fact that they're cousins has deterred quite a few people.
    • Mettaton/Papyrus is also quite popular, due to a single line where Papyrus mentions that Mettaton is his "favorite sexy rectangle".
    • Nice Cream Guy/Burgerpants. Probably because of their opposite personalities, and that an update to Burgerpants' dialogue trees confirmed that they are slightly friendly with each other.
  • Signature Scene: The fight with Sans in the final corridor at the end of a No Mercy run has become the most iconic moment in the game, for its emotional weight, awesome music, and unrelenting difficulty.
  • "Stop Having Fun" Guys: There's a certain way to go through the game that seems to be considered by at least part of the fandom by default to be the "best" or "most complete" way to play, and there are people (most prominently Let's Players) who've been soured on the game or if nothing else on openly partaking in fandom thanks to getting backseat-gamed on a game that, ironically, it's usually agreed a player gets the most of by going into blind and playing naturally. To go into a little more detail, generally, one'll hear that you must complete the Pacifist route first, go to Temmie Village, tell Undyne that anime is real, and then do a "Genocide run" even if you don't want to, and doing voices for the characters that don't match favorite fanon ideas has also gotten people harped on.
  • Suspiciously Similar Song:
  • That One Attack:
    • For first-time players, the Dogi's axe attack. It's the first attack you see that doesn't have an obvious way to dodge it; you have to move underneath the axes as they lift, but it looks dangerous at a first glance, and the attack comes out quickly enough that they might hit you anyway. Since the axes have a huge hitbox, getting hit once means you'll probably get hit again. Combine this with the Dogi's rather complex Spare method, and it's very likely a player will experience their first death by being hit with an axe. Also, if you decide to kill Dogamy, then Dogaressa will switch to only using this attack, and it lasts much longer and goes faster, so death is quick unless you can kill her fast.
    • The very first attack thrown at you by Sans, who is only fought in the No Mercy route, is sadistic, starting out as a very fast corridor of projectiles you must squeeze through and afterwards becoming a gauntlet of large lasers which fire in multiple directions. What makes this worse is that Sans can fire this attack randomly during his introduction speech if you don't beat him on your first try, which makes it easy to get caught off-guard. This is lampshaded by the attacker, who wonders why other enemies don't use their strongest attack first. Their Mind over Matter and penultimate attack are also considered the hardest attacks in his arsenal.note 
    • Undyne's golden spears circle around and behind you right before they hit, making them fairly challenging to block because you need to turn your back on them. This is not insurmountable when there's just a few of them, but eventually she chucks a long volley of nothing but golden spears. Good luck with that.
    • Mettaton's disco ball attack emits white rays that the player can't dodge, along with blue ones that can be dodged by standing still. The player can shoot the disco ball to change white rays to blue ones, but there is no hint that this is possible, leaving many first-time players unable to dodge the white rays.
    • The True Final Boss's Shocker Breaker. Even if you can't die during the battle, this attack consists of huge bolts of lighting quickly being struck down upon the player and you are given very little time to dodge it.
    • Star Blazing from the same fight isn't much better; the massive barrage of stars that covers the bullet board when that last, giant star bursts is borderline impossible to dodge.
  • That One Boss: Has its own page.
  • That One Level:
    • The Core in a Neutral/Pacifist run. While not a particularly long level, the puzzles there can be quite frustrating, and enemy encounters are scripted to happen in certain spots besides just happening regularly. The enemies deal a lot of damage and their attacks are difficult to dodge, and figuring out how to spare them is an involved process that takes multiple turns per monster. Even a Neutral player who chooses to kill them has no solace, as the monsters have weighty defenses and loads of hit points. All of the above is compounded when multiple monsters show up per battle, which is common. And when you finish the Core, Mettaton is waiting at the end.
    • Likewise Hotland, especially on repeat playthroughs. The various puzzles and scripted events combined with Alphys's frequent Annoying Video Game Helper moments cause the zone to drag out compared to the previous zones.
  • That One Puzzle:
    • The piano puzzle in Waterfall is pretty challenging, but not because of a confusing solution. It's actually because, to some people, the correct tune sounds rather different from the music box (on top of the usual tone-deafness and just-plain-deafness issues). Toby seems to have recognized this, because the January 2016 update made the solution reveal itself directly once you activate the music.
    • While most of Mettaton's "fights" are typically fun little minigames that are very hard to actually fail, his colored tile maze puzzle requires you to remember a rather long-winded set of rules which Mettaton himself admits were from "like a hundred rooms ago" and for which the presenter of the puzzle himself gets confused if you ask him to repeat said rulesnote . Even if you do somehow remember all the rules, the puzzle is long enough that you'll only barely have enough time to complete it if you do everything right. Ultimately it's a moot point since just like with the others there's no punishment for failing, though it is noteworthy that this is the only one of Mettaton's puzzles that you're outright expected to fail.
  • They Wasted a Perfectly Good Character:
    • Mettaton has a form you can only see in a No Mercy run, Mettaton NEO, that comes complete with its own theme tune. He still dies in a single hit, just like most of the other bosses in a No Mercy run. Even Toriel and Papyrus got memorable Player Punch death scenes; Mettaton NEO just makes a silly comment about you not wanting to join his "fan club" and then explodes.
    • A lot of fans would have liked to see Muffet's character explored in more detail. More than a few fans have argued that her design and concept alone would have been enough to warrant a larger role in the story. Considering that she's a backer character, her lack of presence is justified, at least.note 
    • Dr. W. D. Gaster. Everything about him (role, fate, relationship with Sans) sounds really fascinating, but you will only get to find about all of this by searching Dummied Out content. Then again, this seems to be the whole point of his character and a possible Sequel Hook.
      • As of the 1.01 patch, Gaster is no longer Dummied Out and both his followers and "mysteryman" have a small probability of appearing in any given playthrough.
  • They Wasted a Perfectly Good Plot: Some believe the idea of getting a better ending by not killing monsters on a second playthrough could have been executed better. Because the first friendly character you meet unsubtly encourages you to not fight the monsters, and the only one who encourages you to kill monsters is rather Obviously Evil, some feel that the impact of killing enemies and facing the consequences of such is lost; these people feel that if the game allowed you to kill enemies before meeting Flowey and Toriel the impact of having killed innocent beings would have been greater.
  • Toy Ship:
    • Asriel/Frisk, due to their interactions in the True Pacifist Ending.
      • Given who he is, Flowey/Frisk would also fall under this trope.
    • Asriel/Chara is also a somewhat popular ship.
    • Chara/Frisk especially in the No Mercy ending. The former can come off as yandere if you choose to destroy the world:
      Chara: You are a great partner. We'll be together forever, won't we?
      • With the recent rise of the idea that Chara is the narrator, new Chara/Frisk depictions show Chara as Frisk's guide and mentor. It also commonly depicts Chara encouraging Frisk through the scary and sad times, while Frisk helps Chara come to terms with what they've done in the past.
  • True Art Is Angsty:
    • Surprisingly, inverted by many fans! One of the biggest complaints is that you can't permanently restore Asriel for a maximum happy ending. Of course, defenders will argue this as to why Asriel shouldn't be saved.
    • Played straight with Sans. His mysterious Dark and Troubled Past and his ever-famous boss battle at the end of the Genocide Route is a huge Fanfic Fuel amongst fans for showing his Stoic Woobie side.
    • Previously played straight with the Fallen Child, but recent shifts in the fandom are beginning to invert this as well. Despite their vague backstory, the first and previously most popular depiction of the Fallen Child was an Axe-Crazy Omnicidal Maniac who only wanted to destroy humanity, using Frisk as their puppet, but now an increasing majority of fans depict them as The Atoner and Frisk's Mission Control, who really did want to free all monsters, no matter what.
  • Ugly Cute: The majority of the cast falls into this. An adorable old goat lady, her equally adorable husband, a pair of wacky skeletons, a fish lady with a Slasher Smile, and a nerdy lizard-like mad scientist. Inverted with Flowey, whose cuteness lasts all of 5 seconds after your first encounter with him. Of course, with the game's relatively simplistic art style, exactly how "ugly" the characters are is debatable.
  • Unintentionally Sympathetic: In a neutral run, the human child can come off as this. The first monster they encountered was Flowey. He gave the impression the underground is a dangerous “kill or be killed” place with monsters popping out of nowhere to attack the child, and the talk of collecting human souls does not help disprove the monstrous flower’s words. They do not harm monsters on the map, showing they do have a distinction of combatants and non-combatants. Also, while they can resurrect from the death, this would not undo any mental trauma that would happen from the event, especially considering the child’s young age. While they do leave the Underground a worse place and become a bit more sociopathic at the end of their journey, the violent actions the child takes to escape the underground can come off as not as unjustified as the game tries to paint.
  • Unintentionally Unsympathetic:
    • While the game tries very hard to make you feel sorry for Dr. Alphys, she came across more as a Bitch in Sheep's Clothing to a few fans. Not only does she run a Monster Protection Racket with Mettaton so she can insert herself into the player's adventure as a hero, but her experiments with determination and monster souls led to the creation of both the Amalgamates and Flowey. Those still leave a bitter taste in a few fans' mouths, especially since she never apologizes or even confesses to the former, despite it being entirely her fault. It's hard to blame her entirely for the latter, since it was an experiment ordered by King Asgore that had Gone Horribly Wrong, and she had no idea what would happen. Either way, she suffers no consequences for either of these behaviors in the game's Golden Ending apart from getting fired (although the other characters are essentially out of a job once they reach the surface), while one of the more sympathetic characters ends up suffering a terrible fate, making a Bittersweet Ending.
    • To some extent, Undyne and the monsters who try to kill you, assuming you're not doing a Genocide or a very violent Neutral run. The story treats any killing of a monster as something horrible... But plenty of these monsters are also actively trying to kill a child to harness their soul to help Asgore commit genocide on the human race, and the former at least is repeatedly played for laughs. While the You Bastard comments are accurate when it comes to the player, In-Universe those monsters don't know that the player even exists and don't know that you can reset (except Flowey and Sans), and yet they act like this moral Double Standard they're holding you to is some inherently obvious truth rather than something brought on by the extreme and uncommon circumstances they don't know about. Even though Blue and Orange Morality is sometimes at work (like with the Vulkins), as some monsters don't seem to realize that their "attacks" are harmful, it's not the case with all of them. For instance, Knight-Knight and Madjick are explicitly stated to be mercenaries hired by Mettaton, meaning they're willing to kill a child for profit! Also, Undyne's words about how you're an "evil" force standing in the way of everyone's "hopes and dreams" lose a lot of their impact, especially in a Pacifist run, when you remember that she's saying it to a child. (And contrary to other monsters, she has seen Human History / Anime, so she probably knows the difference between an adult human and a child.) For an anime fan, she doesn't seem to realize that hurting children is almost always a trait displayed by the villains. She goes as far as trying to kill you after you save a monster child from falling right in front of her. The fact that she remains hostile even after you spare her and even if you continue a Pacifist run (until you befriend her of course) may also make Undyne lose some sympathy, as it may make her look stubborn in her hatred and ungrateful.
  • Unpopular Popular Character: Papyrus. In the game, he somehow has a negative follower count on the Undernet, and his only guaranteed friends are Undyne and his brother. In real life, he's one of the most popular characters in the game and very few people dislike him.
  • Viewer Gender Confusion:
    • Many a player and let's player mistook Alphys for a male at first, not noticing her Tertiary Sexual Characteristics (her big eyelashes). It doesn't help that she's hardly referred to with female pronouns until she actually appears in person.
    • Many people tend to mistake Mettaton for a female due to his EX form having curvy legs, pink stilettos, long hair and being a bishonen.
    • A number of fans (and at least one reviewer) mistook Undyne for a male, although she's referred to with female pronouns even before you fight her. Even then, she spends her initial encounters with you in a bulky suit of armor, and when she takes off her helmet, her scales are shown to be blue (traditionally a masculine color). Combine that with her Hot-Blooded personality, and it isn't hard to see where the confusion comes from.
  • Watch It for the Meme: Given that is essentially a Fountain of Memes in game form, and said memes are harder to avoid than the most Bullet Hell attacks in the game, it was a given. Lampshaded by a few late players:
    "I don't get it. It's a bunch of memes and a soundtrack."
  • What an Idiot: Flowey appearing in front of Chara after learning that he isn't exempt from the "kill or be killed" mentality in the genocide route.
    • You'd think: Flowey would run and hide from Chara for as long as possible, or at least until he was able to fight back. He knows full well that Chara kills anyone they see without regard as to who they are.
    • Instead: Flowey appears right in front of Chara, finished off an almost dead ASGORE, and claims he was useful and should be spared.
    • As a result...: Chara brutalizes Flowey until he's practically dead.
  • What Do You Mean, It's for Kids?: Undertale is intended to be a family-friendly game (and really, even such notoriously nightmarish sequences as Photoshop Flowey and the True Lab aren't that much worse than what's seen in, say, Kirby), to the point that Toby Fox encourages using an alternate tag on Rule 34 posts to hide explicit content from younger players. However, many who have embarked on a No Mercy Route will say that it pushes the boundaries of "family-friendly" to their limits. The game fully allows you to murder every last member of the game's lovable cast if you want to, ultimately enabling an Eldritch Abomination in the form of a cute child to break free and destroy everything in the game world. Possibly Fridge Brilliance, since the two bosses exclusive to this route are Nintendo Hard enough to test the patience of many adult players; it's unlikely a little kid would actually see them through to the end until they're older. A parent could also make a point that even if it does offer such family unfriendly options, the game condemns such actions harshly. Unlike, say, Grand Theft Auto, the game itself scolds you as early as the Ruins for acting violent.
  • The Woobie: Has its own page.

http://tvtropes.org/pmwiki/pmwiki.php/YMMV/Undertale