History YMMV / Undertale

** Like explained below, the Endogeny fight ends with the goofy "Dogsong" playing. While it would normally sound ridiculous, it sounds like a relief here, because [[https://www.youtube.com/watch?v=2Pf_liZf5I8 this song was playing before]], and also because it shows that deep down, it's a BigFriendlyDog who was more curious than aggressive and needed affection before anything else.

** Like explained below, the Endogeny fight ends with "Dogsong" playing: while it negates a lot of its scariness, it's a relief to see the monster doesn't want to attack you anymore, but it also shows that despite everything, it's still a dog who finally found the affection it needed.

** A possibly deliberate example. The battle against the [[spoiler: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.

** Temmie is a cute cat-dog hybrid creature with long hair, who wears a striped shirt and who makes funny faces, but also a young woman who works as a shopkeeper to afford college studies. This plot point gives fanartists the ideas of drawing her as a more conventional dog and CatGirl (either UsefulNotes/{{Furry}} or LittleBitBeastly), transforming her funny clothing as a more skimpy one, and suggesting faster ways she could pay her tuition fees.

** [[spoiler:W. D. Gaster]] bears a striking resemblance to [[http://knowyourmeme.com/photos/1193357-scp-foundation this]] artwork of [[Wiki/SCPFoundation SCP-]][[http://www.scp-wiki.net/scp-1599 1599]].

** Because Undyne is one of the most human-looking monsters, fan-art often portrays her as a [[BuxomIsBetter busty]] AmazonianBeauty (though the busty part is just as often forgone), when she's actually pretty scrawny and flat-chested. Also, while she only has a [[WesternAnimation/AvatarTheLastAirbender Zuko]]-like haircut (a ponytail with the rest of the hair shaved), many depictions of Undyne without her armor (but also graphics enhancing mods, like ''VideoGame/UndertaleBitsAndPieces'' before the 4.0.0 version) showed her with a more feminine haircut[[labelnote:note]]In the original material, she actually has a similar haircut during Alphys' date, making it a small discontinuity[[/labelnote]].

*** The song's main melodies sound quite similar to parts of ''Franchise/TouhouProject''[='s=] [[https://www.youtube.com/watch?v=8jJZA-O_B78 U.N. Owen Was Her]].

** 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 [[spoiler:treated her ex-husband Asgore questionably]]. [[spoiler:She's also an example of BaseBreakingCharacter since some of Asgore's defenders take it too far and make a RonTheDeathEater out of her]].

* DamnYouMuscleMemory: Those who have played ''VideoGame/{{Deltarune}}'' might be used to [[CloseContactDangerBenefit grazing bullets to gain TP]]. There's no TP in ''Undertale'', but ''Deltarune'' players might still get close to attacks out of habit.

* DamnYouMuscleMemory: Those who have played [[VideoGame/Deltarune]] might be used to [[CloseContactDangerBenefit grazing bullets to gain TP]]. There's no TP in ''Undertale'', but ''Deltarune'' players might still get close to attacks out of habit.

* DamnYouMuscleMemory: Those who have played ''VideoGame/Deltarune'' might be used to [[CloseContactDangerBenefit grazing bullets to gain TP]]. There's no TP in ''Undertale'', but ''Deltarune'' players might still get close to attacks out of habit.

** 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}}, coupled with his usual flamboyant personality. There are other players who claim that Mettaton is a [[spoiler:"female ghost]] inside a male body." Despite [[spoiler:his backstory being a potential allegory for being transgender,]] this is not the case. Mettaton goes by male pronouns consistently throughout the game [[spoiler:and, like Napstablook, used they/them pronouns as a ghost]]. There is no reason whatsoever to believe that he was ever female. He's just InTouchWithHisFeminineSide.

** Many people tend to mistake Mettaton for a female due to his EX form having [[HesGotLegs curvy legs]], pink stilettos, long hair and being a {{bishonen}}, coupled with his usual flamboyant personality. There are other players who claim that Mettaton is a [[spoiler:"female ghost]] inside a male body." Despite [[spoiler:his backstory being a potential allegory for being transgender,]] this is not the case. Mettaton goes by male pronouns consistently throughout the game [[spoiler:and, like Napstablook, used they/them pronouns as a ghost]]. There is no reason whatsoever to believe that he was ever female. He's just InTouchWithHisFeminineSide.

** 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 DefrostingIceQueen {{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.
%%** [[spoiler:Pacifist Frisk]].

** Temmie is a cute cat-dog hybrid creature with long hair, who wears a striped shirt and who makes funny faces, but also a young woman who works as a shopkeeper to afford college studies. This plot point gives fanartist the idea of drawing her as a more conventional dog and CatGirl (either UsefulNotes/{{Furry}} or LittleBitBeastly), transforming her funny clothing as a more skimpy one, and suggesting faster "ideas" about how she could pay her tuition fees.

** Some fans were confused on the Mad Mew Mew doll (from the UsefulNotes/NintendoSwitch version) and what pronouns to use, as she is inhabited by the same ghost as the Mad Dummy (who was often interpreted as male before this), leading some fans to wonder if she's UsefulNotes/{{transgender}}. Ghosts are genderless and take on the sex of their host body.

** W.D. Gaster exists in the grey area between this trope and an official character. He is mentioned by some [=NPCs=] but never actually appears in the game, other than a sprite in the files which most fans believe is him. Despite not appearing, he is one of the most popular Undertale characters due to his cool backstory, mysteriousness, and possible relation to Sans and Papyrus.

** A very obscure and likely unintentional case: in his Omega/Photoshop form, Flowey bears a striking resemblance to a flipped version of the [[Myth/AztecMythology Aztec deity]] [[https://www.mexicolore.co.uk/images-6/603_01_2.jpg Tlaltecuhtli]], who had to be kept satiated by human sacrifices. An uncanny fit for a character who is powered by the SOULs of children sacrificed by monsters.

** The Human Child[[spoiler:/Frisk]] is often drawn [[WhoWearsShortShorts wearing shorts]] due to the limited pixel art of the game, but a simple look on [[https://ksr-ugc.imgix.net/assets/011/533/904/f58978f175eba8065d1b5afe4545876d_original.png?ixlib=rb-4.0.2&crop=faces&w=1552&h=873&fit=crop&v=1463684109&auto=format&frame=1&q=92&s=e3cc8b22a13b5f5efcf34ad2793dac51 the official art]] shows that they're wearing pants [[spoiler:(the same applies for the Fallen Human/Chara)]]. However, this example is less true with time, considering [[https://pbs.twimg.com/media/EtueUT9XIAMu_I1.jpg more official art]] shows them wearing shorts.

** While the ''WesternAnimation/StevenUniverse'' fandom normally gets along quite well with the ''Undertale'' fandom, as seen below under FriendlyFandoms, there is one thing that gets ''Steven Universe'' fans upset with ''Undertale'' fans. The song [[https://www.youtube.com/watch?v=6OWq38TikzU "Stronger Than You"]], sung by Garnet in the ''Steven Universe'' episode, "Jail Break", received a [[https://www.youtube.com/watch?v=4TzVOLOROkM 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, [[ParodyDisplacement and some people even think that the parody is the original]].[[note]]This is despite "Jail Break" airing before ''Undertale'' was released.[[/note]] Needless to say, ''Steven Universe'' fans and ''Undertale'' fans who have HypeBacklash towards Sans were not happy with the result. Generally, the ''WesternAnimation/StevenUniverse'' fanbase is split between the group that hates the ''Stronger Than You'' Undertale parody and the group responsible for it.

** In [[spoiler:the secret "Dog Room"]], it's revealed that the Annoying Dog (Toby Fox's AuthorAvatar) programmed Undertale by barking into a text-to-speech device. [[https://www.deltarune.com/update-092020/ The real Toby Fox experienced a chronic pain flareup in his wrist while developing]] ''VideoGame/{{Deltarune}}'', and had to use text-to-speech to make the game.

** Some fans were confused on the Mad Mew Mew doll (from the UsefulNotes/NintendoSwitch version) and what pronouns to use, as she is inhabited by the same ghost as the Mad Dummy, leading some fans to wonder if she's UsefulNotes/{{transgender}}. Ghosts are genderless and take on the sex of their host body.

** Papyrus, ''oh, so very much.'' He loves puzzles, wears armor that is actually just a costume he used in a party once (calling it his "battle body", according to Sans), collects action figures, has a racecar bed, and is looking for friends and respect. His "date" with you just cranks this UpToEleven, as he has to rely on a manual to be able to know what to do.

** Deliberately invoked with a boss fight so difficult that it's practically [[VideoGameCrueltyPunishment punishment]]. If a player decides to go on a Genocide/No Mercy run, they'll find their progress being blocked by [[spoiler:Sans, the lovable comic relief skeleton]]. With them being [[CurbStompBattle over an order of magnitude tougher than anything else in the game]] at the start of the battle [[UpToEleven and getting even tougher as it proceeds]], this RouteBoss is not to be taken lightly. The No Mercy path may be completely optional ([[spoiler:a fact that Sans repeatedly makes clear throughout the battle]]), but [[WhatTheHellPlayer don't you want to see everything in the game?]] The boss isn't hard just because the game conditions are at their toughest. It's because [[SNKBoss the boss bends the rules]], IE his HP being 1, but him [[spoiler:dodging all the attacks till the very end]]. [[spoiler:From the very start, he takes the first turn of the fight, uses one of his strongest attacks first with no warm-up, and can skip his opening monologue to hit you with said attack on subsequent tries. He dodges everything, and all his bullets do one point of damage, but they don't give you MercyInvincibility - they do one point of damage '''per frame'''. And ''on top'' of that, they inflict "Karmic Retribution" that drains your health even further ''after'' contact. The battle only progresses each time you try to attack him, meaning each usage of a healing item is another barrage. Halfway through the battle (after a NonStandardGameOver chance disguised as an alternate ending), Sans starts teleporting you into different attack patterns, requiring quick reactions, ''[[InterfaceScrew attacks while you're in the menu,]]'' and eventually [[ThatOneAttack launches one of the longest attacks in the game as a grand finale]].]] In the end, nothing in the game even comes close to being as hard, and the boss's infamy has become known both in and out of the game's fandom. Ironically for this trope, the fight is one of the reasons [[spoiler:Sans]] is so well-liked.

** Sans quickly became the game's main EnsembleDarkhorse as a result of [[spoiler:his HiddenDepths in the Genocide Route as someone whose mostly-ambiguous DarkAndTroubledPast results in him being [[SadClown deeply apathetic behind his goofy exterior]], and for being an insanely strong {{Superboss}} who breaks the rules of the game in creative ways]]. He became a popular subject for fanworks, especially alternate universe fics that [[spoiler:emphasized his depression]]. However, his popularity grew so rapidly that it led to a widespread backlash both in and out of the ''Undertale'' fandom, causing his and the game's presence in pop culture to collapse in on itself in 2017. By the time he became a Mii Fighter costume in ''VideoGame/SuperSmashBrosUltimate'' two years later, Sans became better-known as a subject for ironic memes that played off his past overexposure, with his fandom being seen as a cautionary tale about what happens when an EnsembleDarkhorse gets too popular too quickly. In fact, a good portion of jokes about [[spoiler:fellow {{Superboss}} Spamton]] in ''VideoGame/{{Deltarune}}'', who garnered a similar reputation, revolve around being next in line to effectively be the next Sans.

** Despite being the most notable RPG to allow non-violent ways to deal with monsters, ''Undertale'' isn't the first RPG to do so. ''VideoGame/PhantasyStarI'' had the ability to talk to certain enemies and talk them out of fighting, though this mainly applied to [[WhatMeasureIsANonHuman humanoid enemies]]. ''VideoGame/UltimaVI'' had the ability to make it through the entire main quest without killing a single enemy, through liberal abuse of invisibility rings and potions.