YMMV / Undertale

The following have their own pages:

• Alternative Character Interpretation
• Broken Base
• Common Knowledge
• Ensemble Dark Horse
• Fanon
• Memetic Mutation
• The Woobie

Other examples:

A-B

• Abandon Shipping:
  • After the Version 1.01 patch released 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 caused a lot of people to jump off the Sans/Gaster ship.
  • Mettaton/Napstablook showed some popularity shortly after the release of the game, probably due to Mettaton's "Would you smooch a ghost" question (and the only possible answer being "Heck Yes!"). This was dropped after spoilers about the game spread and Mettaton and Napstablook being cousins became common knowledge.
• Accidental Aesop: From the Pacifist route: you should always confess your crush on someone else... or your entire species will never know true peace.
• 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's most likely referring to the ketchup Sans drinks leaking out of his ribcage (or just being a Cloudcuckoolander), 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.
  • 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... it may come across as Asgore relieving himself in the flowers.
  • 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.
  • "TOO BAD YOU CAN'T PLAY WITH THESE BALLS." Said during the news segment in Hotland about the basketball. It's supposed to mean that they're for wearing instead of, well, being played with like a normal basketball, but...you know. The fact that it's said by Mettaton doesn't make it any better.
• Adorkable:
  • Asgore. You'd think the big, bearded king wearing armor and a cloak, armed with a crimson trident, would rule despotically. Nah. As Papyrus says, Asgore is "a big fuzzy pushover," one who spends most of his time gardening, making tea, trying to bake, and being unable to come up with good names to save his life.
  • Toriel's love of terrible puns and "embarrassing and overprotective but lovable mom" vibe places her safely into this territory.
  • 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 up to eleven, as he has to rely on a manual to be able to know what to do.
  • Sans is nowhere near to his brother's extent, but it's there, despite his laid-back, cool, controlled air — consider his quickness to dole out cheesy puns and apparent fondness for somewhat childish pranks, as well as the fact that according to Papyrus he's something of a sci-fi nerd.
  • Alphys is adorable, fumbling, and nervous and constantly fidgeting or sweating. In the True Pacifist ending, a kiss from Undyne causes her to blush visibly from head to toe, take "9999 damage" and faint!
  • Undyne is a less blatant example than the others, but it is there, most notably in how she genuinely believes that anime is real.
  • So Sorry is a clumsy, nervous, constantly-apologizing artist that's constantly Shy Finger-Twiddling, and is a cute, chubby, floppy-eared dragon wearing a vest and a bowler hat.
• 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."
  • Attempting a Pacifist run after 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." On the other hand, this could be interpreted as "Some mistakes are too terrible to ever be undone. Sometimes things can't be completely fixed."
• Alternative Character Interpretation: Has its own page.
• Alternate Self Shipping: Alternate Universe Fic is extremely popular within the fandom, with several of these alternate universes being rather popular themselves. Some fanworks ship the alternate versions of the characters together; this is especially common with the different versions of Sans. The most popular pairings between the different versions of Sans even have their own ship names.
• Alternate Universe Fic: To a truly absurd degree. Not only are there a truly staggering amount of AUs out there, but pretty much every AU also has a bunch of additional aus based on it. The "Base-AU"s range from the expected, like Underfell (the monsters are evil) and Underswap (roleswap au), to the far more specific (like Reapertale, where the monsters are deities), while the "Sub-AU"s generally consist of some sort of combination, like Swapfell, Reaperfell, etc. Some are simply one of the above AUs with some minor difference, like Flowerfell, which is basically Underfell, except that Frisk grows a yellow flower somewhere on their body every time they reset.
• Aluminum Christmas Trees:
  • The Info text specifies the glitter and sequins on the Glamburger as edible. Edible glitter and sequins do exist, but they're usually used on cakes and similar sweets. The most expensive burger in the world is called a Glamburger, though it uses gold and caviar rather than glitter and sequins.
  • The fish monster Undyne has a relationship with Alphys. Lesbian fish and lizards actually exist in Real Life.
• 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 Specifically that Chara; regular Chara may or may not be significantly less devilish. Nobody's quite sure.^note Although some fans play with the trope a bit, depicting the two characters with angelic/demonic imagery even when they are both portrayed sympathetically.
• 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.
  • Undyne doesn't seem even slightly perturbed when she accidentally burns her house down, and the whole situation is Played for Laughs. If you call her outside the house, leave, come back, and call again, she suggests that this wasn't even the first time she's caused it to burn down.
• 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 in, 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, and the Unexpected Gameplay Change removes the safety net of healing items, 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. And at the end of the True Pacifist Route, Toby Fox included a very specific line for anyone who didn't realize what the game was hinting at:
    Asriel Dreemurr: Frisk... Don't kill, and don't be killed, alright? That's the best you can strive for.
• 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.
• Awesome Ego:
  • Papyrus thinks he is the most awesome person in the whole world. It's hard not to love him because he's always unflinchingly nice and helpful to everyone. He never looks down on others 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.
• Best Known for the Fanservice: For the Furry Fandom, regarding all the animal-looking characters. Toriel, the Ice Wolf, and the Hotland Royal Guards receive special attention.
• Better as a Let's Play: Undertale is a game where the choices you make have consequences, and is generally considered a case of Enjoy the Story, Skip the Game, so many watch let's plays both to consume the story and to see the choices the player will choose to make and how they react to them.
• Big-Lipped Alligator Moment:
  • There's a random event where if you approach the ferry point in Snowdin, you'll get a phonecall asking for someone whose name starts with "G". When the person calling realizes they've got a wrong number, they randomly break into song: "Oh it's the wrong number, the wrong number song / We're very very sorry that we got it wrong!"
  • Onionsan's appearance. They show up, ramble on as you try to walk along the river, have some dialogue choices that don't really make any kind of an impact, and that's the last you ever hear of them. Don't ask Toby about them; 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. Although, just to complicate things, they do make a reappearance in Deltarune.
  • 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 way that makes sense without hindsight. 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 Dogsong 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: There are so many that we needed a whole page to cover all of them!

C-E

• Catharsis Factor:
  • Flowey spends much of his screentime being an Ax-Crazy Jerkass. In fact, his Establishing Character Moment is tricking the player into accepting his "friendliness pellets" and trying to kill you. It's satisfying when you reach the end of the neutral Flowey boss battle and all the stolen souls rebel against him. Then you have a choice to kill or spare, and you make him feel worse if deciding to spare him. It also pays off a Laser-Guided Karma: Flowey tells you what to do to reach the Golden Ending, no matter the route you chose excluding Genocide.
  • Toriel reveals that Asgore killed the human children she took in and rescued. That's why she opposes you leaving the Ruins, and she nearly cries when letting you go peacefully. When they reunite in the Golden Ending, Toriel calls out Asgore for his actions. He is truly sorry, but he did kill six children and broke his ex's heart.
• Character Perception Evolution:
  • Sans quickly became the game's most popular character as a result of his Hidden Depths in the Genocide Route as someone whose mostly-ambiguous Dark and Troubled Past results in him being 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 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 Super Smash Bros. Ultimate 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 Ensemble Dark Horse gets too popular too quickly.
  • For a good while after the game's release, fans near-unanimously saw Chara Dreemur as the game's Greater-Scope Villain, setting the plot in motion by manipulating their adoptive family and acting as the overarching malevolent force in the Genocide Route. However, as time went on, a large subset of fans started pointing out in-game material that seemed to refute this interpretation, leading to a number of other theories gaining substantial traction, ranging from Chara simply being benevolent but misguided to Chara being the narrator or even the player themself. Nowadays, their role is hotly debated among fans as a result of the large amount of ambiguity surrounding them.
• 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 Is Cool: The Human Child 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.
• Creator Worship: Especially with him sharply curtailing his fan interaction not long after the game's release, Toby Fox has become extensively mythologized by the fanbase, to the point that the few times a year that he does post on social media (or since 2022, newsletter updates as well) are always treated as major events. It helps that in addition to making the highly-anticipated Deltarune, he's also contributed to a surprising number of major games since Undertale's release, including by Nintendo. It also helps that Toby has publicly been very lenient about the creation of fangames/remixes and the use of Undertale music and footage in other YouTube videos, having been a former fangame creator himself.
• Creepy Awesome:
  • Is Flowey a terrifying character? Yes. Is he also a fun villain 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 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. There's also the unnamed harmless Amalgamate who simply tucks you in as you go to sleep, which, while spooky as all hell, is also strangely endearing.
  • The Fallen Child. In the Genocide Route, they're a cute, smiling child that's become an unrepentant mass murderer. It doesn't help that a lot of fanart portrays them with various degrees of aging-up and physical attractiveness.
• Crosses the Line Twice:
  • If Tsunderplane is killed, 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.
  • Mettaton NEO is built up with amazing music, an amazing design, and a conversation that just screams "a boss fight is about to begin". And since this seems to be the first big challenge since Undyne the Undying, many let's players and fans in general are hyped to have a Worthy Opponent... and then he goes down in one hit. Cue as many, if not even more fans being either shocked or outright laughing, while Mettaton's last words are him plugging his fan club. And while this bit might not be as intentional, the fact that Mettaton is followed by the true Final Boss, who is in reality Sans, of all people, makes this even funnier.
  • Whenever the fight with Sans isn't awesome or tearjerking, it's this. The fact that it's the lazy skeleton wearing slippers that's kicking your ass while still maintaining his shit-eating grin and attitude, all while doing Nonchalant Dodges and borderline mocking you for thinking he won't think about trying to not get hit by a creature that one-shotted all but one person before him. Special mention goes to getting dunked on. Sure, it's 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 "Dogsong", 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 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.
  • Asgore/Bowser is also a popular one, due to the fact that while they're both fire-powered, well-regarded kings and fathers, and they're also borderline Foils to each other — Bowser is a greedy jerkass, while Asgore is a kind Heartbroken Badass.
  • Shipping Sans with Nagito Komaeda is very popular, though it's very likely that a lot of it is ironic.
• Diagnosed by the Audience:
  • A sizable contingency of fans headcanon Papyrus as autistic. Much of this stems from his Socially Awkward Hero status (to the point where he needs a guide book to know how to act during a date), his tendency to interpret insults towards him as compliments or self-insults, his occasional "childish" behaviors, and especially his deep interests in cooking spaghetti and making puzzles, the latter of which defines a good chunk of his life (and consequently is easy to read as a special interest).
  • While it's never openly stated in-game, Sans' laziness and apathy to almost everything around him other than Papyrus led to a huge portion of the game's fanbase interpreting him as chronically depressed. This is especially true when considering his dialogue during the final battles of both the Pacifist and Genocide routes, which characterize him as having given up in life a long time ago. The latter fight in particular resulted in no shortage of fanfics that emphasized the interpretation of him as depressed.
• Die for Our Ship:
  • Asgore is bashed a lot by the more hardcore Sans/Toriel shippers due to already having a pre-established 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.
  • 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, 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.
• Difficulty Spike: The Pacifist and No Mercy routes are markedly harder than playing normally in Neutral. In Pacifist, you must avoid killing absolutely everything, which means you will not gain any attack power or HP and will have to get really good at dodging. In No Mercy, you have to kill absolutely everything to get super strong, which means lots of grinding to purge all random encounters. The few bosses that can pose a challenge are absolutely brutal; the game will get really easy as you gain EXP and get stronger, till you can one-shot most enemies, including bosses, but two bosses are still capable of giving you a good fight, as they're the toughest in the game.
• Draco in Leather Pants:
  • 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 (albeit to protect them from what she thinks is certain death) 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.
  • In regards to the No Mercy route, there are plenty of fanfics and fan works, such as the first episode of Glitchtale, that portray Frisk as a Reluctant Psycho that's only killing monsters due to the player's/The Fallen Child's control over them, genuinely being remorseful the entire time, and trying to break free from their influence so they can Set Right What Once Went Wrong. While there's plenty of things that are debatable regarding it, one thing that's for certain is they show no signs of this in the actual game, with Frisk/Chara being shown to be a sociopath as soon as you leave the Ruins, often performing actions of their own volition during cutscenes and, if the smiley face above their head for encounters and some of their CHECKs are anything to go by, being more than happy to kill without remorse. In short, they'll only stop if the player decides to do so.
• Dry Docking: A significant portion of Sans' fanbase engages in self-insert shipping with him, and their tendency in the past to be very possessive and hostile towards canon characters who posed as love rivals led to the memetic stereotype of the yandere Sans fangirl OC for a time.
• 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 Dark Horse: See the dedicated page for further details.
• 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.
  • The Wild Mass Guessing page for this game is one of the most prolific this site has to offer.

F

• 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 emphasis on consequences for actions.
  • 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 tends 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 This is due in part to the original having been deleted and re-posted on Youtube some time after the parody's release, giving it a much later timestamp and lower view count than it "really" has. Needless to say, Steven Universe fans and Undertale fans who have Hype Backlash towards Sans were not happy with the result. Generally, the Steven Universe fanbase is split between the group that hates the Stronger Than You Undertale parody and the group responsible for it.
  • These days, the EarthBound fandom ironically has issues with the Undertale fandom. People got tired of people bringing Undertale up in all MOTHER/EarthBound discussions (especially "Sans is Ness" wisecracks), 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 While the song first debuted in an EarthBound hack made by Toby, Homestuck was the first truly popular work with an actual fanbase to feature the song before Undertale. 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.
  • A fair number of Undertale fans aren't too keen on fellow Deconstruction Game Spec Ops: The Line, primarily due to their vastly different approaches when it comes to discussing morality in video games. The biggest hang-up is that The Line criticizes the player for commiting horrible actions despite there being no other way to progress, while Undertale allows you to choose whether to kill people or not.
• Fandom-Specific Plot:
  • The concept of No Mercy Papyrus is quite popular. Fans really love to ask themselves the question "in an Alternate Universe where Frisk/Chara kills Sans first and confronts Papyrus as the Final Boss of No Mercy Run instead, what would happen?" The concept is played in different ways depending on the author, often mixing and matching the different approaches. Sometimes it's played for Rule of Cool, wherein Papyrus shows himself to be Not So Harmless and gives Frisk/Chara the beating of a lifetime, comparable to Sans himself. In other cases, the emphasis is on Papyrus's evolution from lovable goof to vengeance-crazed, broken individual. And occasionally, the author decides that someone like Papyrus simply could never be as cold and vengeful as his brother was, and has him break down in the middle of battle or be unwilling to hurt the Fallen Child.
  • Even in the best ending, you can never really save Asriel Dreemurr, who will eventually revert to being a flower unable to feel love due to his lack of a soul. Fans have long been entertaining the idea of a "Ultimate Pacifist" ending which would allow Asriel to remain himself. In many cases, this involves Frisk pulling a Heroic Sacrifice and giving their soul to Asriel.
  • On the other side of that, there's Frisk taking Flowey out of the Underground with everyone else after the True Ending, where he becomes the resident "grumpy houseplant". This can be played for laughs (as he still has a homicidal streak), for feels (with Frisk trying to teach him how to love again), or both.
  • Another very popular No Mercy fandom plot has Frisk break free of The Fallen Child's influence in a deciding moment (usually the fight with Sans) and making things right with a Battle in the Center of the Mind where they decisively rid themself of The Fallen and You. This is seen as analogous to a player having a My God, What Have I Done? realization during the battle with Sans and resetting the game.
  • Even though Sans canonically does not remember any previous timelines despite having knowledge of them, the opportunity for drama if he did is just too good for many fans to resist. Many fanworks related to the idea don't even bother to contextualize themselves as an AU or anything, the idea is so ubiquitous. Other artists adhere closer to canon, however, and make stories where he has subtle, subconscious memories of other timelines he's been through, often surfacing in the form of nightmares or phobias. This isn't necessarily canon either, but is much more plausible, considering that the emotional impact of your actions on other characters, such as Papyrus and Undyne, does seem to persist across timelines to some degree.
  • Since the two of them apparently showed up in Snowdin out of nowhere one day and have no other family to be found, a lot of fans really like the idea of Sans raising Papyrus by himself when the they were younger. Some use it for character exploration and speculating about their past, while others like it just for how adorable it is.
  • There are a lot of fanfics about the monsters making contact with humans again after the barrier is broken in the True Ending, as well as them adjusting to life on the surface. Some fics also address the possibility that some of the monsters chose to stay underground.
• 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 answers 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.
  • A sans battle where sans, for whatever reason, is stronger or harder to beat seems to be very popular in fangames, as is fighting Chara or Gaster.
  • The idea of fighting Underswap Papyrus, Undertale Sans and Storyshift Chara (Often combining them with other Alternate Universes) at the same time is also quite popular.
• 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.
• Fan Nickname:
  • "Goatmom" for Toriel has caught on due to her appearance and personality. Among the Japanese, particularly Let's Players, Virtual YouTubers, and HoloLive members, she's instead known as "Mama".
  • In the same vein as calling Toriel "Goatmom", Asgore is "Goatdad" and Asriel is "Goatbro", "Goatchild", "Goatkid", or "Goatson."
  • "Skelebros" or the rarer "Bone Brothers" for Sans and Papyrus.
  • Sense, Sanity or SANs is often used on Twitch for Sans, him being the Only Sane Skeleton.
  • The final boss of the No Mercy route is also known by fans as Sans Serif as a pun on "seraph", the highest ranking type of angel.
  • The two strongly polar endings have been labeled "No Mercy" and "True Pacifist", and the range of various endings in between are "Neutral". The former also has a more popular term, the "Genocide" route. It's also occasionally called "Max LV" (since it requires you to do the maximum possible amount of Level Grinding), by people who are uncomfortable calling it Genocide but don't like "No Mercy" for whatever reason. (The term "No Mercy" has also alternately been used for the Neutral ending that results from not sparing anyone, but not going out of one's way to hunt down every last monster.) Among the Neutral endings, there's the "Neutral-Pacifist" ending, in which you spare everyone, but don't go befriend Papyrus, Undyne, and Alphys and visit the True Lab, so you still fight the Neutral ending bosses and get what's pretty much the best of the neutral endings, and can then reload the game and go for the True Pacifist ending without a restart. Meanwhile, the ending received once all the requirements for a True Pacifist ending have been met in a post-No Mercy/Genocide playthrough is popularly called "Soulless Pacifist", a reference to the fact that in order to replay the game at all post-Genocide, the player must sell their soul to the Fallen Child.
  • Going down the No Mercy path has another nickname based on a line of dialog: "having a bad time."
  • Undyne is often referred to as either "Gay fish, "Fish-Waifu", " or "Strong fish." Some fans have taken to calling her "Fish Zuko".
  • Flowey's form at the end of a Neutral run is widely called Omega (and sometimes God) Flowey by fans. In game they're only referred to as their normal name; internally they're called Flowey X, and in the credits they're called Photoshop Flowey.
  • Flowey's theme, "Your Best Friend", is sometimes referred to as the "ice cream jingle".
  • So Cold is the fan nickname of the Snowdrake's Mother, due to her flavor text.
  • The True Pacifist final boss is often called the Absolute God of Hyperdeath, based on his CHECK description (which he's probably hijacked). Other nicknames include Demongoat.
  • The three bosses unique to the Genocide run (Undyne the Undying, Mettaton NEO, and Sans) are often referred to as "the Bad Time Trio." However, in fan work, it's frequently applied to the fan-created trio of Sans, Papyrus in Underswap and Chara in Storyshift (the latter two of which take Sans's place in their respective AUs).
  • Gary for your snail in the Thundersnail minigame, due to it being a clear reference to the SpongeBob episode "The Great Snail Race".
  • The final corridor before the throne room (officially called the Last Corridor) is often called the Judgment Hall because it's where Sans judges you at the end of a playthrough (and fights you in a No Mercy run).
  • In some circles, "Spider Waifu" has caught on for Muffet.
  • Fans have started calling RG 01 and 02 Harry and Scary after they began switching their roles with Bratty and Catty in Underswap works.
• Fan-Preferred Couple:
  • 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's 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 is pretty big, possibly because they're the only humans in the game and it's implied that Chara is the narrator.
  • Chara/Asriel, despite the two being adopted siblings, became steadily more popular as more people began to see Chara as sympathetic. Notably, it is arguably the most popular ship with Japanese and Korean fans.
• Fan Work Only Fans: Due to the popularity of Alternate Universe Fics such as Underswap and Underfell, some people enjoy these AUs without having played the original 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 (or Frisk) 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.
• Fountain of Memes: With the game's punchy and quippy writing style, a lot of its lines quickly became memes among fans, particularly those from Sans, especially those from his famous Genocide route boss battle; Papyrus, whose eccentricity leads to him spouting a bunch of easy-to-remember lines; and Burgerpants, whose weird Ren & Stimpy-esque individual art style tends to stand out along with his being a sort of living dry comedy sketch about being young with big dreams but winding up working a lousy job.
• Friendly Fandoms:
  • With the JoJo's Bizarre Adventure fandom, due to Mettaton EX's rapid posing and the Dummy's penchant for throwing knives and saying synonyms of "useless" repeatedly 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 Project 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.
  • As result of various shout-outs 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.
  • When not being belligerent to one another, the fandom for The Legend of Zelda tends to have fun inserting Link into crossovers with Undertale. Most commonly this ends up being Young Link, who is also a Kid Hero that dabbles with time mechanics like the fallen human, but crossovers using other Links also exist.
  • With Rivals of Aether, due to the fact that they're both indie tributes to classic Nintendo games, as well as a shared furry fandom thanks to both games' use of anthropomorphic animal characters. With the inception of Rivals' Workshop, several mods adding Undertale (and Deltarune) characters have been created, with several of them becoming quite popular.
  • Undertale fans typically get along well with fans of OMORI, owed to how both games provide similarly offbeat dramedy takes on the JRPG formula. Also helping is the fact that Omocat is a close acquaintance of Toby Fox, who based Woshua on her and gave a shout-out to Omori during the Undertale sixth anniversary livestream. Crossover fan content between Omori and Undertale is consequently fairly common.

G-H

• Gateway Series: To Bullet Hell games.
• Genius Bonus:
  • If you approach Mettaton's seemingly-joke train question, you'll eventually find out that 32.058 minutes is in fact the correct answer.
  • Undyne is likely named after "Undine, the Water Spirit", who was mentioned in Faust and is sometimes the name of Non-Disney productions of The Little Mermaid. Undines or ondines are actually one of the four Alchemic Elementals mentioned by Paracelsus (the one for water, obviously).
  • Papyrus paper is created by cutting open plant stems, soaking them to soften them, and then gluing them together. During the soaking process, the pale noodle-shaped strips look a great deal like spaghetti.
  • A very obscure and likely unintentional case: in his Omega/Photoshop form, Flowey bears a striking resemblance to a flipped version of the Aztec deity 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.
• Germans Love David Hasselhoff:
  • Undertale was a well-received game internationally, but it has especially huge followings in South Korea and Japan, gaining a large amount of support from those in the latter country's gaming industry. This led to an official Japanese translation and a Korean fan translation, as well as ports for PlayStation 4, Play Station Vita, and Nintendo Switch, further boosting the game's popularity there. It also received detailed entries in the Pixiv dictionary. And a full orchestral concert in Tokyo.
  • Undertale also appears to have a smaller but sizeable Chinese fanbase, especially via YouTube, with one major easter egg-hunting channel being Chinese.
  • In terms of individual characters, Mettaton consistently ranks among Japanese fans' top characters, due to a combination of his Anti-Villain nature, being the Underground's designated idol, and his very effeminate personality.
• 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 effect 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 a patch.^note The thing you're being told not to do is actually "be in Alphys's room alone and uninvited", but at first glance they seem to be chewing you out for breaking physics.
• Hard-to-Adapt Work: Despite a devoted fanbase, resonant themes, and the potential for gorgeous visuals, a faithful adaptation of Undertale to a non-interactive medium would be exceedingly difficult. The story is intimately tied to video game mechanics as Save Scumming is a recognized in-universe phenomenon. The Story Branching also poses a problem since an adaptation would necessarily excise important material included in the branches that aren't adapted. Most pointedly though, much of the emotional torque of the original game relies on the Player Punch to end all player punches, which would be difficult to pull off in a non-interactive medium where the audience is not responsible for the actions of the characters: the entire game is a Deconstruction of the Sociopathic Hero tendencies of many Role-Playing Games, a genre in which executing enemies in combat is expected and unremarkable, while in another medium it would be harder for the audience to sympathize with Frisk slaughtering Random Encounters, if the creators wanted to adapt the Genocide Route.
• Harsher in Hindsight:
  • 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 threaten the questioner.
  • While having dinner with Sans at MTT Resort, he remarks to the protagonist, "you must really wanna go home. hey. i know the feeling, buddo." Innocuous enough on a first playthrough, but it becomes heartbreaking once you learn more about Sans' backstory. It's heavily implied that he lost his original home and loved ones and subsequently spent years trying to Set Right What Once Went Wrong until he fell into despair and, in his words, "gave up trying to go back".
  • A lot of Flowey's villainous boasts initially seem unremarkable, then become tragic once you know that he's actually Asriel, but the crowner is probably during the Neutral final boss battle, when he delivers this taunt:
  Call for help. I dare you. Cry into the darkness! "Mommy! Daddy!" "Somebody help!" See what good it does you!
  • 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.
  • In the secret "Dog Room", it's revealed that the Annoying Dog (Toby Fox's Author Avatar) programmed Undertale by barking into a speech-to-text device. The real Toby Fox experienced a chronic pain flareup in his wrist while developing Deltarune, and had to use text-to-speech to make the game.
• Hilarious in Hindsight:
  • It's hard to tell if it's this or if he knew ^note the game is pretty heavy on the Funny Animals 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.
  • Another cross-game thing; many people have noticed similarities between Mettaton and securitrons ^note See the page image for TV Head Robot. Likewise, it's a common joke to swap (Photoshop) Flowey's face for Yes Man's.
  • 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.
  • One of Papyrus's phone calls has him suggest that you "write a musical about [your] adventures". Then Undertale the Musical started becoming a thing, with several Follow the Leader examples soon during or after it...
  • One food item you can purchase from the Spider Bakery is a Spider Donut. Come Halloween Season 2017, Dunkin' Donuts is offering the Limited-Time Spider Donut, which thankfully isn't made from spiders.
  • In an episode of Adventure Time, Finn ends up falling down a hole into a cave with strange temporal powers, if he opens his eyes at all it rewinds time back to when he first fell, forcing him to be especially determined as he wanders through the cave blindly with a -_- expression his face much like the player character. It's so coincidental that many fans thought it was an intentional Shout-Out, but with the turnover time it takes to produce an episode it was likely storyboarded months before Undertale came out.
  • Two fan contents released in December 2015 accidentally foreshadowed Mad Dummy's transition to Mad Mew Mew:
    • The fangame Undertale Red revolved around a ghost possessing a humanoid doll.
    • In the cover album Determination he made alongside the electro artist Amie Waters, RichaadEB made a metal reprise of "Dummy!" called "Electric Balboa", which (before the transition to the next song) ends on... meows.
  • During the final boss fight of the True Pacifist route, Asriel declares, "Up until now, I've only been using a fraction of my REAL power!" While the line was always a bit hammy, it became outright hilarious after the rise of the Powerful Shaggy meme in 2019.
  • This is not the last game that Toby Fox would be involved in that includes dogs that absorb legendary artifacts.
  • In Kirby and the Forgotten Land, Lab Discovera bears a lot of resemblance to the True Lab, both being secret laboratories where the main protagonist enters by elevator and fights amalgamates. Even more, in the hard-mode version of Lab Discovera, the villain-associated phrase "And Here We Are" loops in the background, which just so happens to resemble the name of the True Lab's main theme.
  • A book in Undertale discussing the differences between human and monster physiology notes that since humans can't use magic, none of them will ever know the joy of receiving a "bullet-pattern birthday card". No human, it would turn out, except Toby Fox himself, as Deltarune development team member Taxiderby managed to sneak an unused bullet pattern into the Queen fight to celebrate his birthday.
• Ho Yay: One possible conversation with Burgerpants has him talk about how the Nice Cream guy frequently visits him at his job to ask him of his opinions of the jokes on his ice cream wrappers. The specific "joke" mentioned by Burgerpants is one that shows two people hugging with the text "I love hugs!", and the Nice Cream guy is also mentioned to call him "Burgy" and gives him ice cream for free afterward. The conversation can easily read as the Nice Cream guy attempting to flirt with Burgerpants, but Burgerpants being too dense or cynical to realize it.
• Hype Aversion:
  • 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.
  • While Undertale is a great experience, the fandom talks it up too much sometimes for the unfamiliar, and they are also very prone to revealing spoilers (especially on Tumblr). Some people would rather not play the game at all just to avoid the risk of disappointment.
• Hype Backlash: Undertale got a particularly bad case of this due to how the game got extremely popular incredibly quickly combined with an especially aggressive fanbase.
  • The most common criticism from players is that the story is good, but the bullet hell mechanics aren't fun. 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 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, 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. Many of those that do play the game tend 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 accused of "playing the game wrong". A common case is when a Let's Player doesn't know how to spare Toriel, so they kill her, then 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 will 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, then others call the player stupid because by doing that they would just not get to see the charm of the game and lose interest.
    • The most infamous case would have to be Mangaminx. Despite her explaining extensively in the opening video and description that she wanted to play blind, she had gotten the whole game spoiled for her in the comments. 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), ended her playthrough on the intentionally unsatisfying Neutral ending, and refused to play anymore. Her placing it on the top of her "TOP5 most disappointing games of 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 doing it in one go on a livestream and 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.
  • For a good while, if you were to go on any social media page that wasn't STRICTLY related to Undertale and made a public comment referencing this game or even how something about the current page reminded you of it, your odds of getting yelled at to Get Out! for bringing Undertale to that unrelated medium were quite high for many of the reasons listed above and below. This has fortunately become significantly less common since at least 2018.

I-N

• Idiosyncratic Ship Naming: "Fishbones" for Papyrus/Undyne, "Kingdings" for Asgore/Gaster, "Dunkin Donuts" for Sans/Muffet and "Fontcest" for Sans/Papyrus.
• The Inverse Law of Fandom Levity: Undertale is an odd example, as the game is a mixture of quirky, silly and lighthearted moments with a rounded and interesting cast of characters, and Nightmare Fuel inducing scenes with themes such as genocide and unethical experiments with a large quantity of fourth wall breaking (especially in the infamous No Mercy Route). The fandom will either primary focus on the former or the latter.
• 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. As for the Genocide route, other than the two impossibly difficult bosses, most of the enemies can be killed in one hit and most puzzles are already solved or deactivated, leading others to consider the Genocide route as also being too easy and, unlike the Pacifist or Neutral routes, without any sort of feel-good reward for the hair-pullingly frustrating parts. To be fair, the Genocide route is designed to be this way - if it was any fun, its meaning would be all but lost.
• It's Popular, Now It Sucks!:
  • 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%. Soon after that (less than a month after the "Best. Game. Ever." poll ended), there was the 2015 Game of the Year poll where Undertale came in 3rd place with 12.69%.
  • 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: The game's reliance on surprising the player and subverting their expectations combined with a very passionate fanbase means that many things that were meant to be spoilers have become common knowledge.
  • 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.
  • The identity of the Final Boss of the Genocide Route. Sans, the ditzy skeleton being the most powerful enemy in the game was meant to be a big plot twist, but the awesomeness of the fight, the great music that plays throughout, and many memes about Sans led to players discussing it so much that very few people will play the game without being aware of who's waiting for them should they give in to their murderous impulses.
  • A lot of the otherwise spoiler/secret characters, such as Asriel, Chara and the rumored W.D. Gaster, are becoming more common knowledge thanks to their big fandoms sharing a lot of fanwork and shout-outs. The game's Role Swap AUs also bring them up because it wouldn't be fun when, for examples Asriel's name must be censored in role lists, but some still warn of ending-related spoilers and encourage people to play the game first.
• Jerkass Woobie: Flowey, despite being an unabashedly murderous Foul Flower with a God complex, has a pretty understandable and depressing Freudian Excuse. Following Asriel's death after he crossed the Barrier, Alphys injected Determination into Asgore's first golden flower (which had been imbued with much of Asriel's dust when he had died in the garden), giving Asriel a second life as Flowey. He suddenly realized that without a SOUL, he couldn't feel love anymore, with Asgore and Toriel failing to help him rediscover it. Without being able to love anymore, Flowey was eventually Driven to Suicide and successfully managed to kill himself, until his postmortem apprehension caused his Determination to bring him back to his Save Point. Knowing he could bring himself back to life whenever he wanted, he proceeded to help everybody with their problems across multiple timelines, Desperately Looking for a Purpose in Life. Such a long time of helping people began to wear him down, until he decided to kill someone out of curiosity. He was afraid to do it at first, but killing proved to be the thing that revitalized his sense of emotion, leading him to adapt his "kill or be killed" philosophy due to him being physically unable to feel love in any form.
• 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. Helps that out of everyone from Undertale, Sans got in Super Smash Bros. Ultimate as a Mii Fighter alongside his battle music.
  • 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 Alphys is bisexual, Undyne is a fairly obvious Butch Lesbian, the Royal Guards are a Manly Gay pair whose "merciful" path involves engineering a love confession for them, the main character and Monster Kid (and Chara) are gender neutral with they/them pronouns, and the ghosts (particularly Mettaton) becoming corporeal is heavily evocative of transitioning and other characters appealing to the Bara Genre ^note Asgore, the aforementioned Royal Guards, the Aaron monster, the Ice Wolf.
• 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 devious mastermind, 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.
• Low-Level Run: Enforced in the Pacifist route. Since the only way to gain EXP and LOVE is to kill enemies, you'll be stuck at level 1 for the entire game. Which is for the best as "EXP" and "LOVE" stand for "EXecution Points" and "Level Of ViolencE", respectively.
• Magnificent Bastard: Mettaton, the outrageously fabulous and delightfully egotistical celebrity robot, is initially roped into a scheme to help his friend Dr. Alphys befriend the Human Child. He plays the role of a murderous mechanical menace while Alphys "stops him" at every turn, but after he finds himself doing all of the heavy lifting, Mettaton gets sick of playing pretend. Deciding to steal the Child's SOUL so that he may reach the surface and stop King Asgore Dreemurr from exterminating humanity, Mettaton reactivates several deadly traps, hires multiple monsters to kill the Child, and caps it off by locking them into a dynamic battle on live television for the whole Underground to see. No matter what route you choose, Mettaton will always end the game on his terms, ranging from accepting defeat with pride, to sassing the player even as they're dead set on killing everyone.
• 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:
  • The protagonist and the Fallen Child, often shown in fan videos getting dunked on by Sans during a Genocide run. A compilation of these sorts of edited videos can be found here.
  • Asgore. While still having many fanwork focusing on his badass and attractive traits, many fans love to crack jokes about him being cucked by a skeleton, constantly rejected by his ex-wife, killed by a child or a flower or his status as a Giver of Lame Names.
  • Mettaton NEO, who is only encountered on the Genocide route, due to his hilariously anticlimactic battle. He gives a big speech on how he's going to stop you, then suddenly transforms into a new and intimidating looking form... which is promptly destroyed in one hit, and he doesn't even attack you. Fans often crack jokes about how fragile he is, suggesting he can be defeated by lightly tapping or breathing on him. Deltarune takes this even further by having a different character take Mettaton NEO's form for a proper boss fight, complete with said character taking a jab at him as well.
• 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. What tends to make people play it deliberately is that the Level Grinding condition is otherwise so tedious that most people would become aware of it from hearsay, tempting them to try it out.
  • 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.
• 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. The Human Child 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: Killing Flowey and giving your SOUL to Chara in order to play the game again is the point where, short of messing with the game’s configuration files, it becomes impossible to abort a Genocide Route and doing so permanently taints the True Pacifist ending. Even after killing every enemy in Hotlands (which locks you into the Genocide Route ending), it is still possible to abort by resetting the SAVE file.
• Narm:
  • 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 be considered Beyond Redemption for their actions. 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.
  • Naturally, any moment where characters use the Fallen Child's name becomes ridiculous if you entered a silly or insulting name at the beginning.
  • Asriel's title as "The Absolute GOD of Hyperdeath" becomes this if you think about it for too long, since it raises questions like what exactly "hyperdeath" is, how it differs from regular death, and what it means to be the god of such a concept, much less the absolute god of it. It's at around this point where you realize it's just some edgy nonsense title that Asriel made up to sound cool.
• 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 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.
  • Endogeny's battle theme is a succession of muffled barks, but repeated faster and faster to the point it genuinely becomes unsettling, and it ends with the goofy "Dogsong" playing. While it would normally sound ridiculous, it sounds like a relief here, not only because of the previous theme, but also because deep down, it's a Big Friendly Dog who was more curious than aggressive and needed affection before anything else.
  • Wingdings is one of those inherently funny words, and it's a pretty silly font. That doesn't make Dr. W.D. Gaster or the line "Beware the man who speaks in hands" any less chilling.
• Nightmare Retardant:
  • A possibly deliberate example. As explained above, 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.
  • On a No Mercy Run, Chara will have a red text for things they're looking for or recognize from their past life. Among sentences like "Where are the knives?" (when looking in Toriel's drawers) and "It's as comfy as it looks" (while looking at their coffin), you have this gem when you look in Asgore's fridge:
    "No chocolate."

O-P

• Older Than They Think:
  • The remark about why people never use their strongest attack first, uttered by the Genocide route's second exclusive boss. In fact, many bosses do, and they're usually as annoying as one might expect.
  • Despite a very notable for allowing non-violent ways to deal with monsters, Undertale isn't the first RPG to do so. Phantasy Star I had the ability to talk to certain enemies and talk them out of fighting, though this mainly applied to humanoid enemies. Ultima VI had the ability to make it through the entire main quest without killing a single enemy through liberal abuse of invisibility rings and potions; similarly, Quest for Glory I lets you do the same via lots of sneaking.
  • Live A Live has an entire chapter where your encouraged not to kill (human) enemies and instead find other ways to sneak around and avoid fighting them. Getting the best ending in the chapter requires not killing any of the humans in the castle, while going out of your way to kill everyone nets you the worst ending. Considering Toby has cited Live-A-Live as an inspiration for Undertale, this probably isn't a coincidence.
  • Many players treat elements of the game, like Fighting Your Friend, the usage of a karma system to determine the different narrative routes, and using Level Grinding to show narrative consequences, as a unique and special part of the game that no other game has done before. Many have pointed out that all of these aspects have been in older games, a notable example being Shin Megami Tensei as a franchise, which has many of the narrative and gameplay mechanics praised by fans of Undertale, and has been around for many, many years.
  • The track Megalovania quickly became one of the most famous things about the game. Nowadays, it's almost exclusively associated with Undertale, despite the fact that it originated in The Halloween Hack and had also been used in Homestuck beforehand.
• 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^note he considers himself 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!
• One True Threesome: Given Mad Mew Mew's connection to Undyne and Alphys - having been the former training dummy for the former, and implied to have taken her current body from the latter - it's popular to insert her as the third wheel in Undyne and Alphys' relationship, despite her Character Development being based around accepting their relationship and moving on in her current state.
• 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.
• Parody Displacement: "You're gonna have a bad time" is nowadays associated with this game, but the exact same phrase had previously achieved memetic popularity thanks to the South Park episode "Asspen". It isn’t known whether Undertale was deliberately making a reference to it, but it has caused at least a few South Park references to be misidentified as Undertale ones.
• Player Punch:
  • The game asks you to name "the fallen child". It turns out you aren't naming the child you control throughout the game. Rather, you named what could possibly be the true Big Bad of the game, the catalyst behind Flowey's creation.
  • 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, right? Also, Flowey knows what you're doing.
  • 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. He slowly dies, 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 HP to 1, he's so moved by your determination to let him live that he decides to live underground with you and 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 and 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.
• Polished Port:
  • The PlayStation 4 and Play Station Vita versions had to make many technical changes to account for both the differing hardware and Sony's guidelines. And yet, for the most part, they managed to maintain the overall experience of the PC original. These two versions were also released on physical media, a contrast to the digital-only PC version.
  • The Nintendo Switch and Xbox One/Xbox Series X|S versions are similarly polished and even add new content in the form of their unique Dog Shrines. The Switch version adds an entire optional boss in the form of Mad Mew Mew (which unlocks after beating Mettaton EX), while the Xbox versions have a casino slot machine minigame in its place.
• 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)
  • Asgoriel, Torigore or Torigorey (Toriel/Asgore)
  • Sansby (Sans/Grillby)
  • Papyton (Papyrus/Mettaton)
  • Charisk (Chara/Frisk)
  • Chasriel or Chariel (Chara/Asriel)
  • Frans (Frisk/Sans)
  • Friskriel (Frisk/Asriel)
  • Flowisk (Flowey/Frisk)
  • NicePants (Nice Cream Guy/Burgerpants)
• 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.

R-S

• Recurring Fanon Character:
  • Red, an additional humanoid member of the Royal Guard from the fangame Undertale Red, is perhaps one of the most well known OCs in the entire fandom. She frequently appears in fancomics, and appeared as a cameo in the well-received fangame, Undertale Yellow as someone who was apprehended by Martlet because she mistook her for a human. Repeatedly.
  • 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 with a 1/1000 chance of appearing in a run 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.
  • Doge is an unused dog enemy that would have been part of the Royal Guard. She has appeared in multiple fan works, including Inverted Fate. RG 03 and RG 04, two members of the Royal Guard similar to RG 01 and RG 02, are other cut enemies that appear in Inverted Fate and other fan works.
  • Clover is the protagonist of fangame Undertale Yellow and is the owner of the yellow soul. They are one of the most popular interpretations of the other fallen humans in the fandom.
  • Chisk is a fusion between Frisk and Chara that is the subject of many memes and artworks. They are often paired with the quote “fills you with discomfort” because of the uncomfortable expression on their face.
  • Prunsel is a fan character originating from this tumblr post. The poster had a dream where Papyrus was replaced by a giant realistic Faceless Eye staring directly at the viewer, who "spoke" with an ominous red glow that caused the music to cut out. The fandom quickly became enamored with Prunsel due to how creepy yet absurd it was, and began making fanart and shitposts about it. It was an especially big hit on the "r/Undertale" subreddit, with the users treating it as if it were an official character.
  • Baby Bones is a hypothetical third skeleton brother that comes from a post on r/Undertale in which the poster jokingly misinterprets Sans claiming that Junior Jumble is for "Baby Bones" as him talking about another younger brother.
• 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 bitch 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.
  • 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.
  • While Muffet is generally one of the most liked side characters among fandom, people tend to show her attacking the player for no other reason than just for skipping her sale, completely forgetting about the fact that she was tricked into it by Mettaton or Flowey and thus turning her boss fight from a terrible misunderstanding to an attempt at mugging.
• Scrappy Mechanic: Prior to an update that adjusted their color slightly specifically to address these complaints, blue attacks were this for colorblind players who couldn't see green or red, as the shade of cyan used was (respectively) just a hair darker than and all but indistinguishable from harmful white attacks. Considering many bullet patterns require the player to think quickly in order to distinguish between blue and white and avoid taking damage, this was a fairly major issue.
• Self-Fanservice:
  • Because Undyne is one of the most human-looking monsters, fan-art often portrays her as an Amazonian Beauty with a Buxom Beauty Standard figure (though the busty part is just as often forgone), when she's actually pretty scrawny and flat-chested. Also, while in-game her hair consists solely of a ponytail (plus a sidelock during the Alphys date), many depictions of Undyne without her armor show her with a more feminine haircut.
  • 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.To be fair, she might have all that under her robe, but we don't know what she looks like without it.
  • Likewise, Asgore is not only cute, but very manly looking with his Manly Facial Hair 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.
  • The Mystery Man, who is thought to be W. D. Gaster, is a rather ghostly figure, who only vaguely looks human. In fanart, he's often drawn with a slender human-like figure that makes him as close to a Pretty Boy as you can get with his face. Some fans justify it by saying that the Mystery Man we see in game is Gaster after he's been injected with determination despite little suggesting that being the case.
  • 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.
  • 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 Cat Girl (either Furry or Little Bit Beastly), transforming her funny clothing as a more skimpy one, and suggesting faster ways she could pay her tuition fees.
  • 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^note most of these focus more on her out-battle sprite, who looks less deformed than her in-battle one. Other artists tend to give her a posterior the size of a spider's abdomen, or portray her as being into BDSM due to her repeated claims of wanting to tie up the protagonist.
  • 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 Mates: Alphyne generally goes well with any other ship, such as Soriel and Papyton. Alternatively, those who prefer Toriel and Asgore getting back together either end up shipping Sans with a different character or have him be Alone Among the Couples.
• 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 yeah!" 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 their similar personalities and because of implications that Papyrus might have a Celeb Crush on Mettaton, in particular a line where Papyrus mentions that Mettaton is his "favorite sexy rectangle".
  • Nice Cream Guy/Burgerpants is very popular because of their opposite personalities. Because of the fans shipping them, an update added a very hard to find addition to Burgerpants' dialogue tree where he mentions being slightly friendly with him, which fans naturally latched on to.
• Shocking Moments: 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".
• Signature Scene:
  • For many clueless players, the conversation with Flowey if they decided to spare Toriel after having killed her is an iconic moment because of its clever way to show that the game knows everything you do in it.
  • 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.
• Spiritual Successor:
  • The entire game is a very clear homage to the Mother series, especially the pacifist route.
  • The No Mercy route could be considered a successor to the Demon Path from Soul Nomad & the World Eaters, both involving a blank slate character seeking power by murdering everyone and everything around them in a manner that's both tragic and horrific, all while being egged on by an evil supporting character. This is likely unintentional, as Toby has admitted he's never played the game, though Temmie has, having drawn fanart of it back in 2008.
  • The game can also be seen as a Spiritual Successor to Moon: Remix RPG Adventure. In both games, the player character gets sent to a world filled with bizarre creatures that all have colorful personalities and quirks, they gain LOVE to survive (in Moon, this is absolutely necessary to survive, whereas in Undertale, it's completely optional and it's not even "LOVE" in the first place), they have to deal with a malevolent being who decimates the game world and represents the true horror of playing an RPG stereotypically, i.e. killing everything to gain XP, and both have commentary on the very nature of RPGs themselves.
  • The game shares many thematic elements with Nier, such as Humans Are the Real Monsters, parallel timelines, and replaying the game to gain more context on the world and story. Yoko Taro also expressed a desire for Undertale to be translated into Japanese so he could play it.
  • Talking with monsters and negotiating with them, with different attitudes being needed for different monsters? Three different endings, corresponding to the player's morality? Are we sure this isn't a Shin Megami Tensei fangame?
• Squick:
  • During the hangout at Undyne's house, if Frisk flirts with her^note point to her after she instructs the player to point to what they want, Undyne asks incredulously if they're flirting with her and has a disturbed look on her face. If you do it again, she just continues to look disturbed until you point to something else.
  • If you unepuip the Bandage armor that you start the game with, it becomes a healing item. The game makes it clear how unsanitary this is:
    You re-applied the bandage. Still kind of gooey.
• "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:
  • "Bonetrousle" sounds a lot like "Unfounded Revenge" from Mother 3. The songs are even the same length and will sync up pretty darn well when played at the same time.
  • "Metal Crusher" bears a resemblance to the "A-Type" theme from the Game Boy version of Tetris, which is itself a rendition of the Russian folk song "Korobeiniki". Mettaton's other theme, "Death by Glamour", sounds a lot like the Waluigi Pinball theme from Mario Kart DS, and like the songs above, they combine together quite well.
  • "Your Best Nightmare", which plays during the first half of the Neutral Final Boss fight, may remind players of "Hibachi" and "NO REMORSE", the True Final Boss tracks of DoDonPachi dai ou jou and Ketsui, respectively. Fitting, given the Unexpected Gameplay Change for this fight.
    • The song's main melodies sound quite similar to parts of Touhou Project's U.N. Owen Was Her and Mega Man X5's Sigma 2nd.
  • The Final Boss theme of the True Pacifist Run, "Hopes and Dreams / Save the World," has a motif that resembles "Blinded by Light" from Final Fantasy XIII. Though that particular motif is also taken from the end of the opening theme, the similarity is more obvious here due to the guitar part, faster pace, and gradual build-up in both tracks.
  • The opening of "Snowdin Town" sounds like the opening of "Mabe Village" from The Legend of Zelda: Link's Awakening.
  • Bergentrückung, the short tune which heralds the beginning of the final Asgore battle, resembles the Notre Dame motif (most famous for its use in Frollo's Villain Song, Hellfire) from The Hunchback of Notre Dame. In fact, the first six notes of each are exactly the same, only differing in rhythm.
  • The leading voice of Your Best Friend has an uncanny resemblance to the F.U.N. Song from SpongeBob SquarePants; only the rhythm is different.
  • Two of the songs you can play in Napstablook's house, "Spooktune" and "Spookwave", sound quite similar to the Inspector Gadget theme, as SiIvaGunner noticed. They also have noticable similarities to "Happy H. Christmas" (aka "It Is A Mystery").
  • The first notes of "Alphys" (after the synthbass line) sound similar to the Silver Rupee sound effect in The Legend of Zelda: Ocarina of Time.
  • "Another Medium" sounds uncannily like "Secret of the Forest" from Chrono Trigger, as heard here.
  • "Here We Are", the music that plays on the true lab, despite being a remix of Alphys's theme, sounds almost exactly like the Black Omen theme, also from Chrono Trigger.
  • "Battle Against a True Hero" sounds quite similar to "Plain Asia" from Touhou Eiyashou ~ Imperishable Night. It helps that they're in the same key (F minor) and "Battle Against a True Hero" even uses the iconic "ZUNpets" used in many, many tracks throughout the Touhou Project, including "Plain Asia".
  • "Him" or "Gaster's Theme" has been noted to sound similar to "Who... Are You?" from Final Fantasy VII.
  • "Dating Start!" is basically an Undertale-themed remix of Turnabout Sisters from Ace Attorney.
  • Familiar with "Spear of Justice"? Have a listen to "Passionate Duelist" from the Japanese version of Yu-Gi-Oh!. Now don't try and tell me there ain't some similarities.

T-Z

• 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 axed. 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 in the highly likely event that you have to re-fight him after you've survived it once, he'll interrupt his opening monologue to catch you off-guard. Thankfully, this only happens if you've survived the whole thing exactly once. 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 The former being a Gravity Screw with Spikes of Doom that gets faster, the latter a 30-seconds long gauntlet of attack finished off with a Beam Spam in excess of 100 shots in less than 10 seconds.
  • 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's no hint at all that this is possible, leaving many players sitting ducks.
• That One Boss:
  • Deliberately invoked with a boss fight so difficult that it's practically punishment. If a player decides to go on a Genocide/No Mercy run, they'll find their progress being blocked by Sans, the lovable comic relief skeleton. With them being over an order of magnitude tougher than anything else in the game at the start of the battle and getting even tougher as it proceeds, this Route Boss is not to be taken lightly. The No Mercy path may be completely optional (a fact that Sans repeatedly makes clear throughout the battle), but 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 the boss bends the rules, IE his HP being 1, but him dodging all the attacks till the very end. 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 Mercy Invincibility - 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 Non-Standard Game Over chance disguised as an alternate ending), Sans starts teleporting you into different attack patterns, requiring quick reactions, attacks while you're in the menu, and eventually 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 Sans is so well-liked.
  • Mettaton EX is the hardest boss in a Neutral/Pacifist run. Unlike the bosses before him, his attacks vary dramatically and can do a ton of damage. Adding to this is the Ratings mechanic to the fight, which can be a bit of a Guide Dang It! in how to raise it above a certain threshold, which is required to spare him.
• 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.
  • Fittingly, Hotland/Core is this on a Genocide run as well due to the number of kills (40) being more than the three previous areas combined. Additionally, there aren't that many screens in either area that encounters occur in, and there's no character interactions or dialogue to make things more interesting, so the whole thing drags on much longer than other areas. Then again, considering it's the Genocide Route, this may have been intentional.
• 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.
• They Copied It, So It Sucks!: Many people consider many elements of the game, from the battle system to specific in-game sprites, to be rip-offs from the Mother / Earthbound Series. They resent how many things certain people attribute to Undertale actually came from Mother to begin with.
• 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 Of note is that, for the uninitiated, almost everything about Muffet points to her being one of the main characters. Her existence is properly foreshadowed (however slightly) through the spider bake sales, she has the kind of appealing design typically reserved for main characters, and she even uses a special SOUL color in her battle—which, again, is otherwise something that only happens in the boss fights of major characters. So of course she promptly vanishes after the battle and, unless you backtrack, is never seen or heard from again.
• They Wasted a Perfectly Good Plot:
  • Some believe that the player should have been given a chance to fight monsters before meeting Flowey and Toriel, if not just push meeting them to later in the game. Because Flowey, the only character who encourages you to kill the monsters, is rather Obviously Evil while Toriel, the first friendly character, unsubtly encourages you not to fight them, 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. Delta Rune took this route with strange beings attacking Kris and Susie, as well as Lancer challenging the "party" to a fight before Ralsei can give a tutorial.
  • Hard Mode (activated by entering "FRISK" as your name when starting a new game) is an interesting change of pace, effectively turning on a Silliness Switch while putting you up against enemies from The Core as well as monsters exclusive to Hard Mode. Sadly you only get as far as the Toriel fight before the game ends, informing you not to count on a full version of Hard Mode.
  • While "MEGALOVANIA" is widely regarded as a badass fight theme for Sans the skeleton at the end of the "No Mercy" route, there's a fair number of players that also think similarly of "Song That Might Play When You Fight Sans", and are disappointed that it's an unused song on the soundtrack.
• Toy Ship:
  • Asriel/Frisk is popular due to their interactions in the True Pacifist Ending, which includes the possibility of them hugging.
  • Asriel/Chara is also a popular ship, despite the two of them being adoptive siblings. In particular, Asriel's dialogue in the True Final Boss fight directed at Chara is basically an Anguished Declaration of Love.
    Asriel: I... I... I'm doing this because I care about you, Chara! I care about you more than anybody else!
  • Chara/Frisk has a few possible interpretations. The former can come off as yandere in the No Mercy ending if you choose to destroy the world and interpret their words as referring to Frisk rather than the player, commenting that they're "a great partner" and they'll "be together forever". With the rise of the idea that Chara is the narrator, later depictions of the ship show the former as the latter'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.
• Underused Game Mechanic: Mettaton's mini-games are entertaining little diversions to the normal gameplay; however, not only can you not replay them once they're finished, they're rigged so you can't lose, so much of their potential is lost.
• 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. Of course, with the game's relatively simplistic art style, exactly how "ugly" the characters are is debatable.
• Unfortunate Character Design: Some have pointed out that your playable character's (aka Frisk's) yellowish skin combined with their closed or "squinty" eyes resembles a racist east Asian caricature. Their race isn't confirmed any which way, but some fans still consider the design to be in poor choice.
• 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 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. Not only this, but the player character is stalked around the underground by Undyne, who thinks of herself as a hero despite trying to kill a child (and everyone else praises her as a hero, too). Nearly everyone you meet, barring Papyrus and Monster Kid, engage in morally dubious acts towards the child, from death threats to attempted murder to threatened abduction.
• Unintentionally Unsympathetic:
  • If you're not doing a Genocide or a very violent Neutral run, there's the monsters who try to kill you. The story treats any killing of a monster as something horrible... But plenty of these monsters are actively trying to kill a child to harness their SOUL to help Asgore commit genocide on the human race. While any You Bastard! comments are accurate when it comes to the player, In-Universe the vast majority of monsters don't know about the player nor do they know that you can reset, and yet they act like this moral Double Standard they're holding you to is an inherently obvious truth rather than something brought on by extreme and uncommon circumstances they don't know about. Even though Blue-and-Orange Morality is sometimes at work because some monsters don't realize their "attacks" are harmful, it's not the case for all of them; a few are explicitly stated to be hired mercenaries, meaning they're willing to kill a child for profit!
  • Undyne's actions can easily come off as being unjustified unless the player's killed a lot of monsters. Her speech about how you're an "evil" force standing in the way of everyone's "hopes and dreams" loses a lot of its impact in most runs when you remember she's saying it to a child. Unlike most monsters, Undyne probably knows the difference between an adult human and a child because she's seen human history/anime. For an anime fan, she doesn't seem to realize that hurting children is almost always a trait displayed by villains. She continues trying to kill you after you save a monster child from falling right in front of her, and remains hostile even after you spare her and if you continue a Pacifist run unless you befriend her; this may also make Undyne lose some sympathy for looking stubborn in her hatred and ungratefulness.
  • Although she's by no means a hated character, some people view Toriel as such. While Asgore has a complex sense of morality in that he doesn't want to bring anyone to harm, but feels he has to do so for the sake of his people, as well as trying to delay the inevitable, Toriel's sense of morality is much more simple and closed-minded, thinking that Asgore is an irredeemable monster for doing something he didn't even want to do in the first place. Even her compromise of Asgore crossing the barrier with one soul and taking six other souls is flawed, as while Asgore did take the longer, more arduous route, Toriel is completely forgetting about what happened to her son after he crossed the barrier with innocent intentions. It also doesn't help that once you fall into the Underground, Toriel's first instinct is to take you in, presumably for the rest of your life.
• Unpopular Popular Character: Papyrus. In the game, he somehow has a negative follower count on the Undernet^note he says he's twelve followers away from double digits, meaning he has -2 followers, 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 heavily focused-on curvy legs, pink stilettos, long hair and being a Pretty Boy, coupled with his usual flamboyant personality. There are other players who claim that Mettaton is a "female ghost inside a male body." Despite his backstory being a potential allegory for being transgender, this is not the case. Mettaton goes by male pronouns consistently throughout the game 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 In Touch with His Feminine Side.
  • 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. Combine that with her Hot-Blooded personality, and it isn't hard to see where the confusion comes from.
• Viewer Name Confusion:
  • The name of Ruins monster Whimsun is often misspelled as "Whimsum" in the fandom.
  • It's rather common to see Napstablook's name misspelled as "Nabstablook".
• 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 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. The game also touches on extremely dark themes to varying degrees of subtlety - multiple characters are suggested to be suffering from depression and other serious mental illnesses, and the specific act of suicide is touched upon no less than four times^note Five depending on how you interpret Asriel's comment about why Chara climbed Mt. Ebott, with the two most explicit and unambiguous examples involving characters who are children. What's the ESRB rating for the PS4 and PS Vita versions? E10+! 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.
  • A different source of this is that the game is based on subverting RPG and general gaming conventions, which would only be completely effective on people who have had many years of experience with videogames.
• Woolseyism:
  • Whimsun gets a name change in the Japanese translation to "Nakimushi." Nakimushi idiomatically means "crybaby" in Japanese, but literally translates to "crying bug".
  • Snowdrake speaks with heavy Kansai-ben in the Japanese translation, due to the Kansai dialect's association with comedy acts.
  • Mettaton's "cooking show" Cooking With A Killer Robot gets the wonderful translation of さつじんロボのキラキラキッチン, Satsujin Robo no Kira Kira Kitchen. Literally this would mean something like "Homicidal Robot's Sparkling Kitchen," but the word kirakira here pulls double meaning as the onomatopoeia for "sparkling" and the homonym of "killer."
  • Unlike every other main character, Papyrus's dialogue is written top to bottom, right to left, the "traditional" way Japanese is written, most likely to highlight his rather grandiose way of speaking.
  • In Japanese, a common response to a bad joke is to say it's "cold" (samui), meaning the Japanese translation got to add a couple of extra gags in the snowy area before Snowdin, notably during Sans's bad jokes and the fights with the wannabe comedian Snowdrake.
  • Japanese Undertale fans spent a lot of time debating as to whether Sans would use ''boku'' or ''ore'' as a personal pronoun, only to be shocked when previews of the official translation showed him using ''oira'', a lesser known Japanese pronoun among English speakers that typically is associated with characters with rural roots or "country bumpkin" types. This caused waves in the Japanese fandom that came to be known as "oira shock". It also helps that Snowdin, the area he lives in, is rural-ish itself. It also is a clever way of showing how Sans tries to project a loser-ish, slacker image. During the "Lost Souls" fight and segments before he fights you on the worst route, he switches to ore.
• The Woobie: Has its own page.
• Writer-Induced Fanon:
  • There is a lot of evidence pointing to Chara/The First Fallen Child being the narrator of the game, and this is believed by a significant portion of the fandom.
  • It's never explicitly stated in-game that the six humans that fell into the Underground between Chara and Frisk were also children like them, though there's enough evidence to support it (i.e. all the coffins in New Home being the same size) that many fans take it as canon.

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