History Undertale / TropesAToG

** [[spoiler:This is outright discussed on the Genocide run during the segment in New Home, Flowey points out that he tried helping everyone, but eventually that got boring, so he tried killing everyone. He did everything he could differently in every way he could think of until he exhausted every possible outcome and began to see the people of the underground as predictable, scripted actors repeating the same dialogue over and over, so he mostly sat around waiting for something to happen. This makes him a pretty clear in-universe stand in for the type of player who plays a game to death just to squeeze every ounce of gameplay and dialogue out of it, no matter how callous or cruel the actions they take are.]]

* AloneWithThePsycho: During a True Pacifist run, the fight with Undyne can come off as this, even with other characters potentially watching. You have the option to [[spoiler: flee Undyne if your heart goes back to normal, and she will chase you and keep challenging you.]] While in other runs such as Genocide this comes off as ProperlyParanoid on Undyne's part, in True Pacifist you are an actually harmless child and she is ''hunting you down''. Sans notices, but all he does is briefly distract Undyne by sleeping on the job, allowing you to make it to Hotland.

** The Genocide route's final boss' last attack ([[spoiler:smacking you silly against the borders of the box]]) also deals unavoidable damage. [[spoiler:Unfortunately for him, it also can't kill you. He also has a box-covering attack which he uses when you try to spare him, and this one ''will'' kill you.]]

* AntiClimaxBoss: [[spoiler:Invoked trope: on a Genocide Run, Toriel, Papyrus, Muffet, Mettaton NEO, and Asgore, as well as several mini-bosses, go down in one hit due to your intense murderous desire. Mettaton NEO is especially noteworthy because it's set up to look like he's going to be an upgraded version like Undyne was.]]

** Some characters try to talk you into quitting the game outright. [[spoiler:After getting the best ending, Flowey begs you not to reset the timeline. On a Genocide run, Sans tries his damnedest to make you quit out of frustration, and the Fallen Child would rather move on to other games after destroying the Underworld.]]
* TheApocalypseBringsOutTheBestInPeople: In many ways, the player sees the best side of each character [[spoiler: during the Genocide route, which sees the death and destruction of all things if taken to its conclusion. Papyrus realizes the value of the friends he already has and stops being so desperate about proving himself, then perishes forgiving you and affirming his hope that you can change. Undyne takes a mortal blow for a monster child, then gathers the determination of the entire world to keep fighting until her body gives out. Mettaton reveals as clearly as possible his unselfish love for humans and monsters alike trying to talk you down. Alphys rises to the occasion to save as many monsters as possible from your rampage and becomes a leader and a hero in her own right. Even Sans, implied to know what would happen if you successfully complete the route, finally shakes free of his apathy to battle you head to head with all his incredible strength]].

** "[[NothingIsScarier But nobody came.]]" The phrase not only appears in a couple specific instances of the Pacifist/Neutral route (such as when you fight [[spoiler:the three Memoryheads]]), but seeing that phrase in the encounter screen is a surefire way of knowing that you are now in a Genocide run. [[spoiler:It also crops up when Flowey talks about when he first woke up as a flower.]]

** It's been observed that eyes seem to be significant, with the left eye possibly representing violence. The meter that appears when attacking is shaped like an eye, and [[spoiler:on the Genocide route, we not only see that Mettaton appears to be missing his right eye, but both Undyne and Sans get a brightly glowing left socket.]] When Sans is joking around on a normal route he will wink by closing his left eye, but when he winks during [[spoiler:his boss battle]] he closes the right eye, leaving his left open. And finally, the player's attack option is always on the left and mercy is always on the right.

* AscendedMeme: The rumors that you could get a Real Knife in the demo become truth in the full version. [[spoiler:On a Genocide route, it'll replace the Worn Dagger in New Home.]]

* TheBadGuyWins: If a Genocide run is complete, [[spoiler:the First Child takes control of the protagonist, who then proceeds to destroy the rest of world. What's even worse is that this permanently affects the game and they win ''forever'' even after getting True Pacifist ending.]]

** If you do a second Genocide run, the Fallen Child's speech will change, suggesting you try something different next time. [[spoiler:Because now that they have your SOUL, completing the True Pacifist path will let them out into the world to wreak havoc without your influence.]]

* BewareTheSillyOnes: Sans is introduced as a terrifying presence stalking you through the woods...up until he lets loose with a ridiculous "whoopee cushion in the hand" gag. From that point on, he presents himself as a lazy, laid-back comic relief character who'd rather hang out with you at the local restaurant than actually do his job. But it's implied he knows ''far'' more about the situation than he lets on. [[spoiler:Late in the game he reveals he promised Toriel that he'd watch over and protect you -- and if not for that, he'd have killed you when you left the Ruins. On a Genocide run, he's the last fight and the hardest boss in the entire game.]]

** The ''entire game'' becomes progressively bleaker and bleaker on a Genocide run, and it's especially noticeable if you've done a less murderous run earlier. The point when it really begins to show is Snowdin Town; the normal run town is the most populated area in the game, but it's almost entirely abandoned in a Genocide run, and most of the flavor text has been changed to be much darker.
* BloodFromTheMouth: Seen only on a Genocide run [[spoiler:after dealing the lethal blow to Sans. Though it might actually be ketchup.]]

** You can pull an ISurrenderSuckers on the first boss, dealing a OneHitKill. On a Genocide run, the final boss can pull the same trick on you, to the same effect.

** On the Genocide run, you'll be one or two-shotting literally everything anyway, with one exception, [[spoiler:and the Real Knife is functionally pointless by the time you reach it. The only weapon that's particularly worth your while after Undyne the Undying is the humble Burnt Pan, since it grants a slight bonus to HP gained from food, and you'll need a ''lot'' of food for fighting Sans.]]

* BraggingRightsReward: The [[spoiler:Real Knife]] and [[spoiler:The Locket]] grant stat boosts of 99 to ATK and DEF, but you'll have no real use for them because [[spoiler:by that point of the Genocide path, the only enemy left renders your stats pointless. This ties with the game's themes of guilting the player for their destructive actions, as they could very well drive things that far just for the sake of power growth and the satisfaction of seeing the Real Knife fan rumor become truth.]]

** Getting the Genocide ending again after getting it the first time will result in a massive session of LeaningOnTheFourthWall. [[spoiler:The First Child discusses the nature of leveling up in [=RPGs=] and getting stronger through murder. The game very heavily implies that the First Child is a personification of player characters in [=RPGs=]: an absurdly strong, completely evil, invincible entity that is summoned into a game as your pawn, allowing you to reset the world and mess around with its inhabitants to your liking with the ability to perform resets (read: New Game) and endless retries (read: Saving and loading).]]

* BrilliantButLazy: Sans the Skeleton appears to be extremely knowledgeable about almost everything that goes on in the game, but spends all his time loafing around and making puns for his own amusement. [[spoiler: It is heavily implied that Sans is some form of time traveler/scientist that has observed multiple timelines. The reason he's so lazy is because he knows the truth about how easily the world can be reset regardless of what he does. Only on the full genocide route, where the main character becomes an irredeemable killer, does Sans actually become motivated enough to fight.....and he's by far the hardest boss in the game.]]

** In the Pacifist run, when you first encounter [[spoiler:Asgore]], he greets you with a bit of small talk. Later, in the Genocide run, [[spoiler: Sans]] repeats the conversation almost verbatim.

** [[spoiler: The First Human]] also appears to be this. It's debatable how evil they were originally, but by the time you reach the end of the Genocide route, it's quite clear they have devolved into something much worse, as people are unable to even recognize them as [[spoiler: human]] anymore.

** Sans' laziness is also given a similar treatment. [[spoiler: He's aware that you have been resetting the timeline. Knowing that everything he does will amount to nothing since you can undo it whenever you want, he finally just stopped caring. He only breaks his nonintervention to stop the player from completing a Genocide file, the only outcome that can never be fully taken back.]]

** [[spoiler: Sans. He seems like a simple joker at first - though he can be a bit scary early on in the Genocide run - but as you find out later, he is the ''only'' reason you were able to make it as far as you did. In fact, he's been helping you all along - after all, what would a sentry from Snowdin be doing outside of his station, selling items that just so happen to help raise your health?]]

* CriticalHit: While it isn't a game mechanic per se, there is something like it present; [[spoiler:In a Genocide run, attacking almost any major character will cause you deal an ''extremely'' high amount of damage in a single attack, almost instantly causing death. This is caused by them being caught unprepared and by your LOVE and Determination being especially potent on the most prominent characters.]]

* CruelAndUnusualDeath: At the end of [[KillEmAll Genocide]] route, [[spoiler: you get to butcher Flowey repeatedly into smaller and smaller pieces until he's totally gone. Considering most fights end with a clean kill, be it from massive damage or a sneak attack, this is easily the most brutal way to die in the entire game.]]
* CruelTwistEnding: If you follow a Genocide run with a Pacifist run. [[spoiler:Everything seems to be normal... up until the last moment, in which it's revealed that they player character has been possessed by the Fallen Child, who is then implied to kill everyone and everything.]]

** Once you're on-track for the Genocide ending, the same thing happens to every area theme in the game.

** Due to very different tempo and instrumentation, it's not obvious, but "Battle Against a True Hero" ([[spoiler:found when fighting Undyne in the Genocide route]]) uses a melody which is very similar to "Spear of Justice" ([[spoiler: Undyne's usual battle theme in Neutral and Pacifist Runs]]). The similarity is due to the fact that [[spoiler: "Spear of Justice" showcases Undyne as a HotBlooded, bombastic warrior who is filled with undue enthusiasm about attacking you, while "Battle Against a True Hero" shows the same character in a more solemn, serious state as a heroine trying to hold out hope in the face of unspeakable evil that seriously threatens to plunge everything into death and despair.]]

** Undyne is extremely tenacious, regardless of how your approach her. Particularly if you choose to Fight her or take the Genocide route. [[spoiler: In both cases, upon taking fatal damage, she maintains her form through sheer willpower and continues to fight. In the former case, becoming invincible to damage but slowly weakening until she disappears. In the latter case, she reforms herself into Undyne the Undying, and becomes one of the most difficult combat encounters in the game.]]

** YOU (yes, you!!), the player, in the Genocide route. [[spoiler:Lampshaded by Sans in the final boss fight, where he points out that he "knows your type", and that you're clearly just engaging him - a [[NintendoHard brutally hard]], [[SNKBoss borderline-unfair]] boss - not out of any greater ideal, but just because it's a challenge that was put in front of you.]]

* DifficultySpike: The Pacifist and Genocide 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 Genocide, 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.

** A Genocide run requires you to do much more work that any other run, killing every random encounter in each area (''all'' of them; you won't discover there's a finite amount unless you're a habitual grinder). Other than that, [[SubvertedTrope it is way easier than a normal or pacifist run]] because [[spoiler:most bosses get one-shotted by your evil and hatred]], but has some ''tremendous'' {{Difficulty Spike}}s in [[spoiler:Undyne the Undying and Sans]]. All this for the worst ending in the game.
** If you want, you can do the Genocide run ''again'' after you do it once, with the same results; [[spoiler:the Fallen Child even questions you for it]]. Doing a Pacifist run after you [[spoiler:sell your SOUL to the Fallen Child]] also doesn't go well.

* EasyLevelsHardBosses: To a heavy degree. Standard enemies, while not effortless, can usually be spared either instantly or after a single ACT, with only a few exceptions, and attacking them will bring them down pretty quickly, especially if you've gotten good with weapon timing and have higher LV. Bosses (at least the ones from Papyrus and beyond) are another story; they have high health, they employ BulletHell with their attacks, they mix up the dodging system, and Sparing them requires either a thoughtful series of actions or dragging the fight out for quite a while (over 20 or more turns for the major bosses; most enemy battles will take 2-4 turns at the most). This is especially true in the Genocide path; you can plow through enemies with ease, but anything that can take more than a hit from you is far harder to beat than anything on other routes.

* EvilerThanThou: Should you choose the Genocide path, [[spoiler: [[BigBad Flowey]] would ''tremble'' in fear while desperately begging you not to kill him, even finishing off Asgore in an attempt to please you. You were unimpressed, and ''butchered him to pieces'' before going out and ending all life. Even your motivations are different. The Pacifist ending revealed that deep, deep inside Flowey, Asriel just wanted someone to be with so he won't be alone. But you, you do things ForTheEvulz.]]

** Taking the full Genocide route [[spoiler:eventually subverts this. The amount of encounters in this route that don't go down in one or two turns can be counted on one hand. But those encounters are the most challenging in any route of the game.]]
* EvilOnlyHasToWinOnce: In full force on a Genocide run. The few characters who can stand up to you will most likely kill you over and over again... [[DeathIsASlapOnTheWrist but you have Determination on your side to bring you back from the dead]] and they don't, so unless you reset, they're ultimately fighting a hopeless battle. Likewise, [[spoiler:completing a Genocide run just once is all the Fallen needs to destroy the world and steal your SOUL, which negatively affects all subsequent True Pacifist playthroughs.]]

** [[spoiler: Sans]] is described as "the weakest enemy," with only 1 ATK and DEF. [[spoiler: Indeed, his attacks only do 1 damage, and a single hit will kill him (like anything else on a Genocide run), but ''[[BulletHell just try surviving long enough to actually hit him.]]'' Also, while his attacks do indeed do 1 damage, there is GenocideInvincibility in this battle. Even a slight scrape [[CycleOfHurting can shave off a lot of health]].]]

** [[spoiler:The concept of Genocide Papyrus is quite popular. Fans really love to ask themselves the question "in an AlternateUniverse where Frisk/Chara kills Sans first and confronts Papyrus as the FinalBoss of Genocide 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 RuleOfCool, wherein Papyrus shows himself to be NotSoHarmless and gives Frisk/Chara the beating of a lifetime, comparable to Sans himself. In other cases the emphasis is on Papyrus' evolution from [[CorruptTheCutie 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 Sans was, and has him break down in the middle of battle or being unwilling to hurt the Fallen Child.]]

** You in the Genocide path. Toriel will realize this if you kill her after sparing her.
** It's also an important part of the backstory. [[spoiler:After being taken in by Toriel and Asgore, the "Fallen Child" attempted to manipulate their son Asriel into ''murdering their entire village.'' The end result was that the two of them died, with Asriel being reborn as Flowey. The Fallen Child shows no remorse for this, and on a Genocide run they'll gladly see both of their adoptive parents killed.]]
** Within the Genocide path, [[spoiler: it's implied that Flowey's been helping you on your journey by, among other things, solving puzzles for you, just so that you could focus on your goals of destroying everything in your path. You eventually repay his help by killing him.]]

* FinalBoss: [[spoiler:Photoshop Flowey on Neutral and Sans on Genocide. Asriel, while the True Final Boss of the game as a whole, is technically this for True Pacifist, as well.]]

** During the Genocide run, when you first encounter Sans and don't laugh at his joke, he mutters to himself, "gee, lady, you really know how to pick em, huh..." At first it seems like he's talking to you, but really, he's talking about [[spoiler: Toriel, who asked him to spare any humans he encountered.]] Due to the nature of the run, however, you wouldn't discover this unless you had previously done a Pacifist run.

** [[spoiler:When Sans warns you that you will have a bad time and disappears during the Genocide run, it is a strong implication that Sans is self-aware and can access the same meta concepts as the player, as no other character has been able to simply teleport out of nowhere and reappear at will.]] He can also do this during the Pacifist run, when you are trying to solve a puzzle at the bottom of a cliff and [[spoiler:Sans is at the bottom, waiting at both ends of the screen although we never see him move. He lampshades this by asking if you are following him, and stares straight at the player instead of at Frisk while he's idle.]]

** '''The Apathetic''': [[spoiler: Sans. His knowledge of the ability to SAVE left him broken and finds reaching to the Surface no longer satisfying.]] Though he will break this way of thinking to battle and try to stop you in the Genocide run.

** The game dives into this full force at [[spoiler:the end of the Genocide run. The boss tries to convince you to stop playing, and things get even worse in the ending itself.]] And it gets even ''worse'' than that if you [[spoiler:try to restart the game after that.]]

* FromNobodyToNightmare: [[spoiler:You, if you choose to take the Genocide run. You go from attacking common monsters to mutilating bosses in one hit to ''destroying the world'' with help from the Fallen Child. All because you were bored.]]

** Under certain circumstances, the GameOverMan is different: Being defeated by [[spoiler:Photoshop Flowey]] causes him to taunt you during the Game Over screen instead after [[spoiler:Asgore]] says his usual line while [[spoiler:being tricked by Sans' fake spare during the Genocide run]] will cause Dogsong to play instead of the regular Game Over theme while instead of [[spoiler:Asgore's usual quote, Sans will assert that, after all that you've done, he'll never be your friend again.]]

** At various points throughout the game, the player is given the option to Fight a given character during a cutscene. If the player chooses to Fight, the basic slashing animation will be used for the attack regardless of whatever weapon you actually equipped. [[spoiler:At the very end of a Genocide Run, the Fallen Child will also make the decision for you]].

** Mettaton does this a lot. [[spoiler:If you play a Genocide route up until him, but flub the requirements on his boss battle (because you didn't kill everything in his zone before encountering him), he'll say that he can tell that you struck him with less than absolute hatred, and that he can therefore die peacefully knowing that while you might kill Asgore, humanity and Alphys are safe.]]

** Arguably, the way to achieve the worst ending (ie. Genocide / Genocide route). While the game guides the player quite clearly to the best ending ([[spoiler:Flowey always tells you what you missed at any neutral ending you get]]), even the existence of such a worst ending is not clearly hinted, nor the way there instructed. This is deliberate, because [[spoiler:it means that there is nearly no chance a player will end up on the route accidentally; a major theme of the route is that the player themselves is choosing to kill absolutely every monster (despite it being unnecessary and tedious) abecause they want to know what happens if they do]].

** Napstablook doesn't have a "damaged" sprite or sound effect. Your attacks aren't actually doing anything, and they're just reducing their HP out of politeness. After "depleting" his health, he leaves, and because the battle accomplished nothing, the game tells you, word-for-word, that "You lost one experience point." [[spoiler:Observant players will notice that the game specifically says "experience point" here, while normal battles call it EXP; extremely observant players will check their status menu and notice that they didn't actually lose any EXP. This is because "Experience Points" don't exist; EXP, or "Execution Points", is just a term coined by monsters for how someone's ability to kill develops. You don't learn this until Sans' judgement at the other end of the game.]]

%% Note: The route for the worst ending, aka the "No Mercy" route, aka the "Genocide" Route, does NOT have an official name. Therefore, call it whatever you want. To avoid edit wars, please don't make edits that do nothing but change one term to the other. The wiki isn't the official source of information for the game.
%%

** [[spoiler:This is outright discussed on the No Mercy run during the segment in New Home, Flowey points out that he tried helping everyone, but eventually that got boring, so he tried killing everyone. He did everything he could differently in every way he could think of until he exhausted every possible outcome and began to see the people of the underground as predictable, scripted actors repeating the same dialogue over and over, so he mostly sat around waiting for something to happen. This makes him a pretty clear in-universe stand in for the type of player who plays a game to death just to squeeze every ounce of gameplay and dialogue out of it, no matter how callous or cruel the actions they take are.]]

* AloneWithThePsycho: During a True Pacifist run, the fight with Undyne can come off as this, even with other characters potentially watching. You have the option to [[spoiler: flee Undyne if your heart goes back to normal, and she will chase you and keep challenging you.]] While in other runs such as No Mercy this comes off as ProperlyParanoid on Undyne's part, in True Pacifist you are an actually harmless child and she is ''hunting you down''. Sans notices, but all he does is briefly distract Undyne by sleeping on the job, allowing you to make it to Hotland.

** The No Mercy route's final boss' last attack ([[spoiler:smacking you silly against the borders of the box]]) also deals unavoidable damage. [[spoiler:Unfortunately for him, it also can't kill you. He also has a box-covering attack which he uses when you try to spare him, and this one ''will'' kill you.]]

* AntiClimaxBoss: [[spoiler:Invoked trope: on a No Mercy Run, Toriel, Papyrus, Muffet, Mettaton NEO, and Asgore, as well as several mini-bosses, go down in one hit due to your intense murderous desire. Mettaton NEO is especially noteworthy because it's set up to look like he's going to be an upgraded version like Undyne was.]]

** Some characters try to talk you into quitting the game outright. [[spoiler:After getting the best ending, Flowey begs you not to reset the timeline. On a No Mercy run, Sans tries his damnedest to make you quit out of frustration, and the Fallen Child would rather move on to other games after destroying the Underworld.]]
* TheApocalypseBringsOutTheBestInPeople: In many ways, the player sees the best side of each character [[spoiler: during the No Mercy route, which sees the death and destruction of all things if taken to its conclusion. Papyrus realizes the value of the friends he already has and stops being so desperate about proving himself, then perishes forgiving you and affirming his hope that you can change. Undyne takes a mortal blow for a monster child, then gathers the determination of the entire world to keep fighting until her body gives out. Mettaton reveals as clearly as possible his unselfish love for humans and monsters alike trying to talk you down. Alphys rises to the occasion to save as many monsters as possible from your rampage and becomes a leader and a hero in her own right. Even Sans, implied to know what would happen if you successfully complete the route, finally shakes free of his apathy to battle you head to head with all his incredible strength]].

** "[[NothingIsScarier But nobody came.]]" The phrase not only appears in a couple specific instances of the Pacifist/Neutral route (such as when you fight [[spoiler:the three Memoryheads]]), but seeing that phrase in the encounter screen is a surefire way of knowing that you are now in a No Mercy run. [[spoiler:It also crops up when Flowey talks about when he first woke up as a flower.]]

** It's been observed that eyes seem to be significant, with the left eye possibly representing violence. The meter that appears when attacking is shaped like an eye, and [[spoiler:on the No Mercy route, we not only see that Mettaton appears to be missing his right eye, but both Undyne and Sans get a brightly glowing left socket.]] When Sans is joking around on a normal route he will wink by closing his left eye, but when he winks during [[spoiler:his boss battle]] he closes the right eye, leaving his left open. And finally, the player's attack option is always on the left and mercy is always on the right.

* AscendedMeme: The rumors that you could get a Real Knife in the demo become truth in the full version. [[spoiler:On a No Mercy route, it'll replace the Worn Dagger in New Home.]]

* TheBadGuyWins: If a No Mercy run is complete, [[spoiler:the First Child takes control of the protagonist, who then proceeds to destroy the rest of world. What's even worse is that this permanently affects the game and they win ''forever'' even after getting True Pacifist ending.]]

** If you do a second No Mercy run, the Fallen Child's speech will change, suggesting you try something different next time. [[spoiler:Because now that they have your SOUL, completing the True Pacifist path will let them out into the world to wreak havoc without your influence.]]

* BewareTheSillyOnes: Sans is introduced as a terrifying presence stalking you through the woods...up until he lets loose with a ridiculous "whoopee cushion in the hand" gag. From that point on, he presents himself as a lazy, laid-back comic relief character who'd rather hang out with you at the local restaurant than actually do his job. But it's implied he knows ''far'' more about the situation than he lets on. [[spoiler:Late in the game he reveals he promised Toriel that he'd watch over and protect you -- and if not for that, he'd have killed you when you left the Ruins. On a No Mercy run, he's the last fight and the hardest boss in the entire game.]]

** The ''entire game'' becomes progressively bleaker and bleaker on a No Mercy run, and it's especially noticeable if you've done a less murderous run earlier. The point when it really begins to show is Snowdin Town; the normal run town is the most populated area in the game, but it's almost entirely abandoned in a No Mercy run, and most of the flavor text has been changed to be much darker.
* BloodFromTheMouth: Seen only on a No Mercy run [[spoiler:after dealing the lethal blow to Sans. Though it might actually be ketchup.]]

** You can pull an ISurrenderSuckers on the first boss, dealing a OneHitKill. On a No Mercy run, the final boss can pull the same trick on you, to the same effect.

** On the No Mercy run, you'll be one or two-shotting literally everything anyway, with one exception, [[spoiler:and the Real Knife is functionally pointless by the time you reach it. The only weapon that's particularly worth your while after Undyne the Undying is the humble Burnt Pan, since it grants a slight bonus to HP gained from food, and you'll need a ''lot'' of food for fighting Sans.]]

* BraggingRightsReward: The [[spoiler:Real Knife]] and [[spoiler:The Locket]] grant stat boosts of 99 to ATK and DEF, but you'll have no real use for them because [[spoiler:by that point of the No Mercy path, the only enemy left renders your stats pointless. This ties with the game's themes of guilting the player for their destructive actions, as they could very well drive things that far just for the sake of power growth and the satisfaction of seeing the Real Knife fan rumor become truth.]]

** Getting the No Mercy ending again after getting it the first time will result in a massive session of LeaningOnTheFourthWall. [[spoiler:The First Child discusses the nature of leveling up in [=RPGs=] and getting stronger through murder. The game very heavily implies that the First Child is a personification of player characters in [=RPGs=]: an absurdly strong, completely evil, invincible entity that is summoned into a game as your pawn, allowing you to reset the world and mess around with its inhabitants to your liking with the ability to perform resets (read: New Game) and endless retries (read: Saving and loading).]]

** In the Pacifist run, when you first encounter [[spoiler:Asgore]], he greets you with a bit of small talk. Later, in the No Mercy run, [[spoiler: Sans]] repeats the conversation almost verbatim.

** [[spoiler: The First Human]] also appears to be this. It's debatable how evil they were originally, but by the time you reach the end of the No Mercy route, it's quite clear they have devolved into something much worse, as people are unable to even recognize them as [[spoiler: human]] anymore.

** Sans' laziness is also given a similar treatment. [[spoiler: He's aware that you have been resetting the timeline. Knowing that everything he does will amount to nothing since you can undo it whenever you want, he finally just stopped caring. He only breaks his nonintervention to stop the player from completing a No Mercy file, the only outcome that can never be fully taken back.]]

** [[spoiler: Sans. He seems like a simple joker at first - though he can be a bit scary early on in the No Mercy run - but as you find out later, he is the ''only'' reason you were able to make it as far as you did. In fact, he's been helping you all along - after all, what would a sentry from Snowdin be doing outside of his station, selling items that just so happen to help raise your health?]]

* CriticalHit: While it isn't a game mechanic per se, there is something like it present; [[spoiler:In a No Mercy run, attacking almost any major character will cause you deal an ''extremely'' high amount of damage in a single attack, almost instantly causing death. This is caused by them being caught unprepared and by your LOVE and Determination being especially potent on the most prominent characters.]]

* CruelAndUnusualDeath: At the end of [[KillEmAll No Mercy]] route, [[spoiler: you get to butcher Flowey repeatedly into smaller and smaller pieces until he's totally gone. Considering most fights end with a clean kill, be it from massive damage or a sneak attack, this is easily the most brutal way to die in the entire game.]]
* CruelTwistEnding: If you follow a No Mercy run with a Pacifist run. [[spoiler:Everything seems to be normal... up until the last moment, in which it's revealed that they player character has been possessed by the Fallen Child, who is then implied to kill everyone and everything.]]

** Once you're on-track for the No Mercy ending, the same thing happens to every area theme in the game.

** Due to very different tempo and instrumentation, it's not obvious, but "Battle Against a True Hero" ([[spoiler:found when fighting Undyne in the No Mercy route]]) uses a melody which is very similar to "Spear of Justice" ([[spoiler: Undyne's usual battle theme in Neutral and Pacifist Runs]]). The similarity is due to the fact that [[spoiler: "Spear of Justice" showcases Undyne as a HotBlooded, bombastic warrior who is filled with undue enthusiasm about attacking you, while "Battle Against a True Hero" shows the same character in a more solemn, serious state as a heroine trying to hold out hope in the face of unspeakable evil that seriously threatens to plunge everything into death and despair.]]

** Undyne is extremely tenacious, regardless of how your approach her. Particularly if you choose to Fight her or take the No Mercy route. [[spoiler: In both cases, upon taking fatal damage, she maintains her form through sheer willpower and continues to fight. In the former case, becoming invincible to damage but slowly weakening until she disappears. In the latter case, she reforms herself into Undyne the Undying, and becomes one of the most difficult combat encounters in the game.]]

** YOU (yes, you!!), the player, in the No Mercy route. [[spoiler:Lampshaded by Sans in the final boss fight, where he points out that he "knows your type", and that you're clearly just engaging him - a [[NintendoHard brutally hard]], [[SNKBoss borderline-unfair]] boss - not out of any greater ideal, but just because it's a challenge that was put in front of you.]]

* DifficultySpike: 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.

** A No Mercy run requires you to do much more work that any other run, killing every random encounter in each area (''all'' of them; you won't discover there's a finite amount unless you're a habitual grinder). Other than that, [[SubvertedTrope it is way easier than a normal or pacifist run]] because [[spoiler:most bosses get one-shotted by your evil and hatred]], but has some ''tremendous'' {{Difficulty Spike}}s in [[spoiler:Undyne the Undying and Sans]]. All this for the worst ending in the game.
** If you want, you can do the No Mercy run ''again'' after you do it once, with the same results; [[spoiler:the Fallen Child even questions you for it]]. Doing a Pacifist run after you [[spoiler:sell your SOUL to the Fallen Child]] also doesn't go well.

* EasyLevelsHardBosses: To a heavy degree. Standard enemies, while not effortless, can usually be spared either instantly or after a single ACT, with only a few exceptions, and attacking them will bring them down pretty quickly, especially if you've gotten good with weapon timing and have higher LV. Bosses (at least the ones from Papyrus and beyond) are another story; they have high health, they employ BulletHell with their attacks, they mix up the dodging system, and Sparing them requires either a thoughtful series of actions or dragging the fight out for quite a while (over 20 or more turns for the major bosses; most enemy battles will take 2-4 turns at the most). This is especially true in the No Mercy path; you can plow through enemies with ease, but anything that can take more than a hit from you is far harder to beat than anything on other routes.

* EvilerThanThou: Should you choose the No Mercy path, [[spoiler: [[BigBad Flowey]] would ''tremble'' in fear while desperately begging you not to kill him, even finishing off Asgore in an attempt to please you. You were unimpressed, and ''butchered him to pieces'' before going out and ending all life. Even your motivations are different. The Pacifist ending revealed that deep, deep inside Flowey, Asriel just wanted someone to be with so he won't be alone. But you, you do things ForTheEvulz.]]

** Taking the full No Mercy route [[spoiler:eventually subverts this. The amount of encounters in this route that don't go down in one or two turns can be counted on one hand. But those encounters are the most challenging in any route of the game.]]
* EvilOnlyHasToWinOnce: In full force on a No Mercy run. The few characters who can stand up to you will most likely kill you over and over again... [[DeathIsASlapOnTheWrist but you have Determination on your side to bring you back from the dead]] and they don't, so unless you reset, they're ultimately fighting a hopeless battle. Likewise, [[spoiler:completing a No Mercy run just once is all the Fallen needs to destroy the world and steal your SOUL, which negatively affects all subsequent True Pacifist playthroughs.]]

** [[spoiler: Sans]] is described as "the weakest enemy," with only 1 ATK and DEF. [[spoiler: Indeed, his attacks only do 1 damage, and a single hit will kill him (like anything else on a No Mercy run), but ''[[BulletHell just try surviving long enough to actually hit him.]]'' Also, while his attacks do indeed do 1 damage, there is no MercyInvincibility in this battle. Even a slight scrape [[CycleOfHurting can shave off a lot of health]].]]

** [[spoiler:The concept of No Mercy Papyrus is quite popular. Fans really love to ask themselves the question "in an AlternateUniverse where Frisk/Chara kills Sans first and confronts Papyrus as the FinalBoss 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 RuleOfCool, wherein Papyrus shows himself to be NotSoHarmless and gives Frisk/Chara the beating of a lifetime, comparable to Sans himself. In other cases the emphasis is on Papyrus' evolution from [[CorruptTheCutie 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 Sans was, and has him break down in the middle of battle or being unwilling to hurt the Fallen Child.]]

** You in the No Mercy path. Toriel will realize this if you kill her after sparing her.
** It's also an important part of the backstory. [[spoiler:After being taken in by Toriel and Asgore, the "Fallen Child" attempted to manipulate their son Asriel into ''murdering their entire village.'' The end result was that the two of them died, with Asriel being reborn as Flowey. The Fallen Child shows no remorse for this, and on a No Mercy run they'll gladly see both of their adoptive parents killed.]]
** Within the No Mercy path, [[spoiler: it's implied that Flowey's been helping you on your journey by, among other things, solving puzzles for you, just so that you could focus on your goals of destroying everything in your path. You eventually repay his help by killing him.]]

* FinalBoss: [[spoiler:Photoshop Flowey on Neutral and Sans on No Mercy. Asriel, while the True Final Boss of the game as a whole, is technically this for True Pacifist, as well.]]

** During the No Mercy run, when you first encounter Sans and don't laugh at his joke, he mutters to himself, "gee, lady, you really know how to pick em, huh..." At first it seems like he's talking to you, but really, he's talking about [[spoiler: Toriel, who asked him to spare any humans he encountered.]] Due to the nature of the run, however, you wouldn't discover this unless you had previously done a Pacifist run.

** [[spoiler:When Sans warns you that you will have a bad time and disappears during the No Mercy run, it is a strong implication that Sans is self-aware and can access the same meta concepts as the player, as no other character has been able to simply teleport out of nowhere and reappear at will.]] He can also do this during the Pacifist run, when you are trying to solve a puzzle at the bottom of a cliff and [[spoiler:Sans is at the bottom, waiting at both ends of the screen although we never see him move. He lampshades this by asking if you are following him, and stares straight at the player instead of at Frisk while he's idle.]]

** '''The Apathetic''': [[spoiler: Sans. His knowledge of the ability to SAVE left him broken and finds reaching to the Surface no longer satisfying.]] Though he will break this way of thinking to battle and try to stop you in the No Mercy run.

** The game dives into this full force at [[spoiler:the end of the No Mercy run. The boss tries to convince you to stop playing, and things get even worse in the ending itself.]] And it gets even ''worse'' than that if you [[spoiler:try to restart the game after that.]]

* FromNobodyToNightmare: [[spoiler:You, if you choose to take the No Mercy run. You go from attacking common monsters to mutilating bosses in one hit to ''destroying the world'' with help from the Fallen Child. All because you were bored.]]

** Under certain circumstances, the GameOverMan is different: Being defeated by [[spoiler:Photoshop Flowey]] causes him to taunt you during the Game Over screen instead after [[spoiler:Asgore]] says his usual line while [[spoiler:being tricked by Sans' fake spare during the No Mercy run]] will cause Dogsong to play instead of the regular Game Over theme while instead of [[spoiler:Asgore's usual quote, Sans will assert that, after all that you've done, he'll never be your friend again.]]

** At various points throughout the game, the player is given the option to Fight a given character during a cutscene. If the player chooses to Fight, the basic slashing animation will be used for the attack regardless of whatever weapon you actually equipped. [[spoiler:At the very end of a No Mercy Run, the Fallen Child will also make the decision for you]].

** Mettaton does this a lot. [[spoiler:If you play a No Mercy route up until him, but flub the requirements on his boss battle (because you didn't kill everything in his zone before encountering him), he'll say that he can tell that you struck him with less than absolute hatred, and that he can therefore die peacefully knowing that while you might kill Asgore, humanity and Alphys are safe.]]

** Arguably, the way to achieve the worst ending (ie. No Mercy / Genocide route). While the game guides the player quite clearly to the best ending ([[spoiler:Flowey always tells you what you missed at any neutral ending you get]]), even the existence of such a worst ending is not clearly hinted, nor the way there instructed. This is deliberate, because [[spoiler:it means that there is nearly no chance a player will end up on the route accidentally; a major theme of the route is that the player themselves is choosing to kill absolutely every monster (despite it being unnecessary and tedious) abecause they want to know what happens if they do]].

** The first formal encounter, Froggit, is the last enemy to see you off at New Home.

** Near the beginning of the game, the player encounters a spider bake sale. Players can put money in a spiderweb and a spider will bring them a donut or some cider. It's a cute and original way to obtain healing items before encountering the first town. [[spoiler: A few areas later, the player meets the spiders hosting the bake sale, who are none too pleased if the player has not supported their enterprise.]]

** An optional one. When exploring the ruins at the beginning, the player can find some spiders' bake sale and can buy some food from them. [[spoiler: This food comes in handy when confronted by the head of the bake sale later on; using the food during the battle shows that you are a friend of spiders and ends the fight.]]

* CreativeClosingCredits: The special thanks portion has you dodging the names of the 918 Kickstarter backers who pledged high enough for that reward.

* AloneWithThePsycho: During a True Pacifist run, the fight with Undyne can come off as this, even with other characters potentially watching. You have the option to [[spoiler: flee Undyne if your heart goes back to normal, and she will chase you and keep challenging you.]] While in other runs such as No Mercy this comes off as ProperlyParanoid on Undyne's part, in True Pacifist you are an actually harmless child and she is ''hunting you down''. Sans notices but his only offers of help is to talk with Undyne for a few minutes, allowing you to make it to the Hotlands.

** A case that's justified and commented on; unlike most [=RPGs=], there's no accuracy or evasion stats; if you pull off the attack, it ''will'' hit, though a few enemies can NoSell it. This is because, while monsters attack your SOUL with dodge-able bullets, you attack them directly and they don't try to avoid it (likely out of MookChivalry), which is just one thing that makes you very powerful if you take advantage of it. In fact, one of the most startling things in the game is when [[spoiler:one of the bosses casually ''dodges your attack''. No, he doesn't block it or anything, he just steps to the side as if it was nothing. After all, why should he stand there and take it if everyone else who did died?]]

* {{Antepiece}}: An odd example. Whenever your SOUL mechanics are changed you almost always have a chance to get used to them before the bosses throw their most dangerous attacks.

** "It's rude to talk about someone who's listening." Has popped up a few times in relation to [[spoiler: Gaster]].

** Getting the yellow flavor text for all the monsters in the Pacifist Ending credits. Most of them aren't so bad since they can be gotten either by experimenting or are required to spare the monster without having to fight. However, there are a few of them that are pretty non-intuitive. Some particular examples include Icecap, which you can spare by ignoring it two times but to get the yellow credits you need to then [[spoiler:steal its hat and then compliment them]], and Aaron, which requires you to [[spoiler:change the background music in Napstablook's house and then encounter him outside with that background music still on]] to get his yellow credits.
** Arguably, the way to achieve the worst ending (ie. No Mercy / Genocide route). While the game guides the player quite clearly to the best ending ([[spoiler:Flowey always tells you what you missed at any neutral ending you get]]), even the existence of such a worst ending is not clearly hinted, nor the way there instructed.

* EmpatheticEnvironment: The save point immediately before the battle with Undyne reads "The wind is howling. You're filled with determination..." If you [[spoiler:kill her, the wind stops, and its message changes accordingly.]]

* CardboardPrison: Papyrus' attempt to use his and Sans' shed as an impromptu prison for the player is quite unimpressive to say the least. His only measure for hindering escape attempts is placing a fence across the room, which has such large gaps between the bars that it can be circumvented by ''walking'' out between them, and the door to the shed turns out to be unlocked. Technically, it was locked, as you can find out if you check it from Snowdin. It was locked from the INSIDE.

** During the boss-fight against [[spoiler: Photoshop Flowey, dying and reloading after saving at least one soul preserves your progress. Possibly because the souls can remember things when you load the game.]]

** If you're killed by Toriel, she'll show a unique sprite for a split-second before you see the game over screen.

** At the beginning of the game, Toriel takes you to her house in the ruins. It's a quaint hovel with three bedrooms, one of which is locked off. [[spoiler: At the end of the game, you reach Asgore's domain, an identical house called New Home. It also has three bedrooms; the room that was Toriel's is locked, and the room in Torie's house that was locked is Asgore's. This visually demonstrates the relationship between Asgore, Toriel, and their children.]]

** Flowey frequently references the game's mechanics such as LV, EXP, and [[spoiler:the player's ability both to save their progress and restart from a save point as well as to reset the game and start over, all of which technically exist in0universe as well as being game mechanics. When he takes over as the final boss of the Neutral path, Flowey even seizes control of the player's ability to save their progress and uses it for himself.]] He even has a couple lines of dialogue for people watching certain paths of the game on YouTube. He also gets rather miffed if you botch his tutorial.

** The most powerful weapon and armor are sitting out for you to take just before you reach the climax of the game, which is handy if you haven't made any investments in upgrading your gear. [[spoiler:Especially nice on a pacifist run, since the next boss is the only one where your ATK stat matters.]]

** Most weapons are useless on a Pacifist run, as you won't be attacking anything. The only weapons that will be of any use are the Torn Notebook (which increases MercyInvincibility) and the Burnt Pan (which increases the power of healing items, but isn't bought). There's also [[spoiler:the Worn Dagger, which you need on a Neutral-Pacifist run if you want to fend off Asgore as well as possible. Once you're on track for the True Pacifist run, you can forget about it]].

** On the No Mercy run, you'll be one or two-shotting literally everything anyway, with one exception, [[spoiler:and the Real Knife is functionally pointless by the time you reach it. The only weapon that's particularly worth your while after Undyne the Undying is the humble Frying Pan, since it grants a slight bonus to HP gained from food, and you'll need a ''lot'' of food for fighting Sans.]]

** The last weapon you can get in the game is the Worn Dagger. [[spoiler: It's description reads "good for cutting weeds". You know, like Flowey's EldritchAbomination form.]]

** At various points throughout the game, the player is given the option to Fight a given character during a cutscene. If the player chooses to Fight, the basic slashing animation will be used for the attack regardless of whatever weapon you actually equipped. [[spoiler:At the end of a No Mercy Run, the Fallen Child will also make the decision for you]].

** The very last chords of "Bring it In, Guys", the theme for the ending credits, are the very first chords from "Once Upon a Time", the first song you hear upon starting the game. [[spoiler:Subverted when it gets interrupted and you get more credits with a different song.]]

* BigBad: Asgore Dreemurr, king of the monsters. Throughout the game it's made quite clear that besides the barrier, he is the only thing between you and your escape from the Underground.[[spoiler:Subverted when you learn that Asgore doesn't actually want to hurt you, but feels as though he has no choice in order to keep a promise he made in a moment of anger and grief when both of his children died on the same day.]].

** [[spoiler:When Toriel confronts Asgore, she tells him that he could've stopped his quest at one human SOUL, crossed the barrier himself, and taken six more human SOULs. Since she mentioned it could've ended their imprisonment peacefully, it stands to reason she meant SOULs from recently-deceased humans, since it's established human SOULs persist after death.]]

** Getting the yellow flavor text for all the monsters in the Pacifist Ending credits. Most of them aren't so bad since they can be gotten either by experimenting or are required to spare the monster without having to fight. However, there are a few of them that are pretty non-intuitive. Some particular examples include Icecap, which you can spare by ignoring it two times but to get the yellow credits you need to then [[spoiler:steal its hat and then compliment them]], and Aaron, which requires you to [[spoiler:change the background music in Napstablook's house and then encounter him outside with that background music still on]] to get his yellow credits.

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"No mercy" is often used to mean a neutral route in which the player kills every monster they come across, but does not actively seek out monsters to kill. Because of this, referring to the worst ending route by this name can create ambiguity. I don't have the authority to make any rules, but I feel I should at least mention this, as it is a source of potential confusion.
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