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*** [[spoiler: ...Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings. ...But now he's gone. And his brother isn't around, either. ...What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone... ...Go ahead. Prepare however you want. But when you step forward... I will KILL you.]]
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*** [[spoiler: ...Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings. ...But now he's gone. And his brother isn't around, either. ...What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone... ...Go ahead. Prepare however you want. But when you step forward... I will KILL you.
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*** [[spoiler: ...Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings. ...But now he's gone. And his brother isn't around, either. ...What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone... ...Go ahead. Prepare however you want. But when you step forward... I will KILL you. ]]
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*** [[spoiler: ...Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings.
...But now he's gone. And his brother isn't around, either.
...What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone...
...Go ahead. Prepare however you want. But when you step forward... I will KILL you.]]
...But now he's gone. And his brother isn't around, either.
...What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone...
...Go ahead. Prepare however you want. But when you step forward... I will KILL you.]]
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*** [[spoiler: ...Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings. \n... ...But now he's gone. And his brother isn't around, either.
...either. ...What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone... \n... ...Go ahead. Prepare however you want. But when you step forward... I will KILL you.]]
...
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*** [[spoiler:...Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings.
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*** [[spoiler:...[[spoiler: ...Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings.
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*** [[spoiler:... Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings. ... But now he's gone. And his brother isn't around, either. ... What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone... ... Go ahead. Prepare however you want. But when you step forward... I will KILL you.]]
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*** [[spoiler:... Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings. ...
...But now he's gone. And his brother isn't around,either. ... either.
...What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone... ...
...Go ahead. Prepare however you want. But when you step forward... I will KILL you.]]
...But now he's gone. And his brother isn't around,
...What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone...
...Go ahead. Prepare however you want. But when you step forward... I will KILL you.]]
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***[[spoiler:... Forget it. Look. Papyrus didn't come to his meeting today. Say what you want about him. He's weird, he's naive, he's self-absorbed... But Papyrus has NEVER missed a meeting. And no matter what time you call him on the phone... Night, day, afternoon, morning... He ALWAYS answers within the first two rings. ... But now he's gone. And his brother isn't around, either. ... What did you do to him? What did you DO TO HIM? Papyrus, who I have trained every day... Even though I KNOW he's too goofy to ever hurt anyone... ... Go ahead. Prepare however you want. But when you step forward... I will KILL you.]]
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* AngstWhatAngst: She doesn't seem even ''slightly'' perturbed when she accidentally burns her house down, and the whole situation is PlayedForLaughs. 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.
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What pronouns a character uses is not a trope.
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* JapanesePronouns: "Watashi", in the official Japanese version.
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* JapanesePronouns: "Watashi", in the official Japanese version.
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* {{Expy}}: Red hair? Check. A [[FieryRedhead passionate and cruel]] personality to go with it? Check. Introduced a third into the series and as being above the protagonists in skill and power? Check. Lives for battle? Antagonizes the blue-clothed character? Check. Uses spears? Check. Large chunks of ShipTease with [[LesYay another female character]]? Check. Are we describing Undine or [[Anime/PuellaMagiMadokaMagica Kyouko Sakura]]?
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* InspirationalMartyr: [[spoiler: If Toriel is alive at the end of a neutral run then she succeeds Asgore, becomes Queen of the Monsters, and ends the war against humanity. However killing Undyne (even if you didn't kill anybody else) will outrage the other monsters enough to overthrow Toriel and plunge the underground into anarchy]].
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* InspirationalMartyr: [[spoiler: If Toriel is alive at the end of a neutral run then she succeeds Asgore, becomes Queen of the Monsters, and ends the war against humanity. However killing Undyne (even if you didn't kill anybody else) will outrage the other monsters enough to overthrow Toriel and plunge the underground into anarchy]].anarchy. If you kill Undyne on during a No Mercy Run then it inspires Alphys to evaucate as many monsters as possible to the True Lab in an attempt to save them.]]
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--> Undyne (Genocide Run): [[spoiler: "Damn it ... so even THAT power ... it wasn't enough? ... Heh ... heheheh ... [[DefiantToTheEnd If you think I'm gonna give up hope, you're wrong]]. 'Cause I've ... Got my friends behind me. Alphys told me that she would watch me fight you ... And [[YouShallNotPass if anything went wrong, she would ... evacuate everyone]]. By now she's called ASGORE and told him to absorb the 6 human SOULs. [[YouHaveNoChanceToSurvive And with that power]] ... [[HopeSpringsEternal this world will live on]] ...!"]]
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--> Undyne (Genocide Run): [[spoiler: "Damn it ... so even THAT power ... it wasn't enough? ... Heh ... heheheh ... [[DefiantToTheEnd If you think I'm gonna give up hope, you're wrong]]. 'Cause I've ... Got my friends behind me. Alphys told me that she would watch me fight you ... And [[YouShallNotPass if anything went wrong, she would ... evacuate everyone]]. By now she's called ASGORE and told him to absorb the 6 human SOULs.[=SOULs=]. [[YouHaveNoChanceToSurvive And with that power]] ... [[HopeSpringsEternal this world will live on]] ...!"]]
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adding final speech
* FinalSpeech: Makes one if she dies. They're different depending on whether you kill her in a Neutral Run or a Genocide Run.
--> Undyne (Genocide Run): [[spoiler: "Damn it ... so even THAT power ... it wasn't enough? ... Heh ... heheheh ... [[DefiantToTheEnd If you think I'm gonna give up hope, you're wrong]]. 'Cause I've ... Got my friends behind me. Alphys told me that she would watch me fight you ... And [[YouShallNotPass if anything went wrong, she would ... evacuate everyone]]. By now she's called ASGORE and told him to absorb the 6 human SOULs. [[YouHaveNoChanceToSurvive And with that power]] ... [[HopeSpringsEternal this world will live on]] ...!"]]
--> Undyne (Genocide Run): [[spoiler: "Damn it ... so even THAT power ... it wasn't enough? ... Heh ... heheheh ... [[DefiantToTheEnd If you think I'm gonna give up hope, you're wrong]]. 'Cause I've ... Got my friends behind me. Alphys told me that she would watch me fight you ... And [[YouShallNotPass if anything went wrong, she would ... evacuate everyone]]. By now she's called ASGORE and told him to absorb the 6 human SOULs. [[YouHaveNoChanceToSurvive And with that power]] ... [[HopeSpringsEternal this world will live on]] ...!"]]
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* FriendToAllChildren: She apparently knows the children that live in Snowdin Woods on a personal basis.
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* FriendToAllChildren: She apparently knows the children that live in Snowdin Woods on a personal basis. [[spoiler: In the Genocide Run, she even saves one of them from you by TakingTheBullet]].
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* LivingOnBorrowedTime: [[spoiler: In the No Mercy run she's able to gain a HeroicSecondWind because she's producing her own Determination. Even if she wins the fight (i.e. she kills you and you decide not to try again) that Determination will still kill her.]]
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* HeroicSacrifice: During the No Mercy Run, she sees you about to kill the Monster Kid and unhesitantly jumps in front of him to shield him from the fatal blow (saving his life at the cost of her own). [[HeroicSecondWind She gets better though.]] [[spoiler: If you kill her when she's Undyne the Undying but don't complete your genocide then her battle with you saved monsterkind from extinction]].
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* LesbianCop: She's a BadassGay who is also Captain of the Royal Guard. In addition to human-hunting she also acts as law-enforcement.
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* InspirationalMartyr: [[spoiler: If Toriel is alive at the end of a neutral run then she succeeds Asgore, becomes Queen of the Monsters, and ends the war against humanity. However killing Undyne (even if you didn't kill anybody else) will outrage the other monsters enough to overthrow Toriel and plunge the underground into anarchy]].
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* RebelLeader: [[spoiler: If Toriel is alive at the end of a neutral run then she becomes Queen and ends the war against humanity. However if during this run you killed Papyrus and/or ten monsters then Undyne spearheads a rebellion to overthrow Toriel and reverse her reforms. Downplayed in that that these conditions being met will spark a rebellion against Toriel even if Undyne is dead [[note]]in fact, her death is also a condition for rebellion. See InspirationalMartyr above[[/note]].]]
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The reason given for removing this implies she's talking about humans having overwhelming power. However, not only is that blatantly contradicted both by enemy behavior and the game's difficulty, but the fact that it's easier to kill than resolve things peacefully only makes sense if the human isn't overwhelmingly powerful. The line was clearly intended to be a dig at the player's behavior and taking the easy way, and she does not have access to that knowledge.
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* RightForTheWrongReasons: When you fight her after having killed people, she'll call you a cold-blooded murderer and immediately reject your protests of self-defense by saying "You didn't kill them because you had to. You did it because it was ''easy''". She is somewhat correct, as the player can reload saves as much as they want and thus arguably has no excuse but to strive for the perfect nonviolent outcome. However, [[BlueAndOrangeMorality how exactly she came to this conclusion]] ''without'' knowing about the fourth wall [[InsaneTrollLogic is anyone's guess]].
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* SenselessSacrifice: If you kill her during a [[FinalSolution No Mercy Run]], her dying words are that she [[YouShallNotPass bought enough time for the rest of the Monsters to evacuate to safty.]] If you continue down this path then she prevented nothing and you
ultimatly kill all the monsters anyway.
ultimatly kill all the monsters anyway.
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* SenselessSacrifice: If you kill her during a [[FinalSolution No Mercy Run]], her dying words are that she [[YouShallNotPass bought enough time for the rest of the Monsters to evacuate to safty.]] If you continue down this path then she prevented nothing and you
ultimatlyyou ultimately kill all the monsters anyway.
ultimatly
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* AsskickingEqualsAuthority: Until you encounter Undyne, the only members of the Royal Guard you've seen are five silly dogs that can be gotten past by petting. When Undyne shows up, she makes it very clear that she's the leader of the guards for a reason. Depending on your actions in the Underground, she might decide that Toriel (who's hardly a push-over herself) is too soft-hearted to become Queen after Asgore's death, and will successfully usurp the throne from her.
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* AsskickingEqualsAuthority: Until you encounter Undyne, the only members of the Royal Guard you've seen are five silly dogs that can be gotten past by petting. When Undyne shows up, she makes it very clear that she's the leader of the guards for a reason. Depending on your actions in the Underground, she might decide that Toriel (who's hardly a push-over herself) is too soft-hearted to become Queen after Asgore's death, and will successfully usurp the throne from her. If Toriel is dead then Undyne gets the throne anyway by being third in line.
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* TheApocalypseBringsOutTheBestInPeople: During a No Mercy run she prevents you from murdering the Monster Kid by jumping in front of him and taking the blow you meant for him. Then she proceeds to fight until the bitter end, making her own determination.
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* SenselessSacrifice: If you kill her during a [[FinalSolution No Mercy Run]], her dying words are that she [[YouShallNotPass bought enough time for the rest of the Monsters to evacuate the area. If you continue down this path then she prevented nothing as you kill all the monsters anyway]].
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* SenselessSacrifice: If you kill her during a [[FinalSolution No Mercy Run]], her dying words are that she [[YouShallNotPass bought enough time for the rest of the Monsters to evacuate the area. to safty.]] If you continue down this path then she prevented nothing as you and you
ultimatly kill all the monstersanyway]].anyway.
ultimatly kill all the monsters
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* SenselessSacrifice: If you kill her during a [[FinalSolution No Mercy Run]], her dying words are that she [[YouShallNotPass bought enough time for the rest of the Monsters to evacuate the area. If you continue down this path then she prevented nothing as you kill all the monsters anyway]].
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* KillAllHumans: [[spoiler: Should she ever become leader of the monsters then this will be her goal]]. See TakingUpTheMantle below.
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* TakingUpTheMantle: Some of the endings of the Neutral Route have her [[spoiler: succeeding King Asgore's as ruler of the Underground and continuing his war to exterminate humanity. If you kill Papyrus or ten monsters then she will usurp the throne from Toriel, banish her to back to the ruins, and if you killed Toriel then Undyne just directly suceeds Asgore]].
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* TakingUpTheMantle: Some of the endings of the Neutral Route have her [[spoiler: succeeding King Asgore's as ruler of the Underground and continuing his war to exterminate humanity. If you kill Papyrus or ten monsters then she will usurp the throne from Toriel, Toriel and banish her to back to the ruins, and if ruins to do this. If you killed Toriel then Undyne just directly suceeds Asgore]].
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* TakingUpTheMantle: Some of the endings of the Neutral Route have her [[spoiler: succeeding King Asgore's as ruler of the Underground and continuing his war to exterminate humanity. If you kill Papyrus or ten monsters then she will usurp the throne from Toriel, banish her to back to the ruins, and if you killed Toriel then Undyne just directly suceeds Asgore]].
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%%* RedOniBlueOni: Red oni to Alphys' blue oni.
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Even human children can kill the most powerful monsters through determination. Undyne doesn't need to know about SAVE or LOAD to grasp that.
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* RightForTheWrongReasons: When you fight her after having killed people, she'll call you a cold-blooded murderer and immediately reject your protests of self-defense by saying "You didn't kill them because you had to. You did it because it was ''easy''". She is somewhat correct, as the player can reload saves as much as they want and thus arguably has no excuse but to strive for the perfect nonviolent outcome. However, [[BlueAndOrangeMorality how exactly she came to this conclusion]] ''without'' knowing about the fourth wall [[InsaneTrollLogic is anyone's guess]].
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[[center: [- [[Characters/{{Undertale}} Top Index]] | '''Major''' ([[Characters/UndertaleTheHumanChild The Human Child]], [[Characters/UndertaleFlowey Flowey]], [[Characters/UndertaleToriel Toriel]], [[Characters/UndertaleSans Sans]], [[Characters/UndertalePapyrus Papyrus]], '''Undyne''', [[Characters/UndertaleAlphys Alphys]], [[Characters/UndertaleMettaton Mettaton]], [[Characters/UndertaleAsgoreDreemurr Asgore Dreemurr]]) | [[Characters/UndertaleOtherCharacters Minor]] | [[Characters/UndertaleMonsterEncounters Monsters]] | [[Characters/UndertaleSpoilerCharacters Spoilers]] ]] -]
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[[quoteright:204:http://static.tvtropes.org/pmwiki/pub/images/image5.png]]
[[caption-width-right:204: [[TheDeterminator NGAHHH!!!]]]]
[[caption-width-right:262:Click [[labelnote:here]]http://static.tvtropes.org/pmwiki/pub/images/the_undying.png[[/labelnote]] to see her Genocide run form.]]
The captain and commander of the Royal Guard that protects the underground. Likes spears. Dislikes humans. [[BreadEggsBreadedEggs Likes throwing spears at humans.]]
----
* ActionGirl: Loves fighting and big swords. What else could she be? But try to hurt her friends, and...
* {{Adorkable}}: No, really. It's downplayed, but it is there, as she genuinely believes that anime is real.
* AffectionateParody: Everything about her seems to be one to common shonen and shojo anime tropes. She appears to be wearing [[Franchise/DragonBall Saiyan armor]]. She even has a transformation involving the hearts of everyone in the world uniting to defeat you on the No Mercy route.
* AmbidextrousSprite: Her overworld sprite is mirrored and leaves a glaring mistake. When walking to the left, Undyne doesn't have her eyepatch on.
* AngstWhatAngst: She doesn't seem even ''slightly'' perturbed when she accidentally burns her house down, and the whole situation is PlayedForLaughs. 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.
%%* AntiVillain
* ArcVillain: Of Waterfall, in the same way that Mettaton is the arc villain of Hotland. Throughout Waterfall, a fairly backstory-heavy level, you're constantly pursued by Undyne, who is intent on killing you, regardless of how you've acted up until this point. Her battle marks the point where you start making great strides towards returning to the surface. Undyne could also be viewed as this to Snowdin, since Papyrus is a total non-threat -- it's wanting to please ''Undyne'' that drives him to fight you.
* ArmorIsUseless: She has negative defense in her boss fight, despite being covered in plate. During her un-armored rematch after the "date", she somehow has more defense.
* AsskickingEqualsAuthority: Until you encounter Undyne, the only members of the Royal Guard you've seen are five silly dogs that can be gotten past by petting. When Undyne shows up, she makes it very clear that she's the leader of the guards for a reason. Depending on your actions in the Underground, she might decide that Toriel (who's hardly a push-over herself) is too soft-hearted to become Queen after Asgore's death, and will successfully usurp the throne from her.
* BadassGay: She's a really tough woman. She also has a thing for Alphys, and asks you to deliver a love letter she wrote to her in the true ending route, because she can't muster the courage to do so herself. And if you call her while in the garbage dump, she'll describe it as "a GREAT place to meet girls."
* BatmanGambit: Records a message on an Echo Flower telling the human to look behind them so she can set up a dramatic ambush. [[spoiler:This flops when Monster Kid shows up.]]
* {{BFS}}: Though Undyne prefers using spears in battle, she keeps a giant sword in her house. Since she believes anime is true, she thinks humans historically have wielded swords up to ten times their size.
* BladeOnAStick: Her weapons are spears, and she seems to be able to summon and throw as many as she wants, often throwing 3 at once or summoning up to 6 through the floor. While they appear to be made of water in the overworld, her battle sprites seem to be holding whole spears.
* BlackKnight: In her first appearances. Her dark armor covers her entire body, disguising her face. She is almost never heard speaking, giving her a very sinister and mysterious vibe. Naturally, she is incredibly powerful and a major antagonist (being TheDeterminator that relentlessly chases you through the whole Waterfall zone). Unusually, she uses spears instead of swords.
* BloodKnight: Loves fighting. In fact, it's impossible to spare her when you engage in combat -- you have to run away, as she refuses to accept your mercy.
* BlueIsHeroic: Her skin is blue, and while she's not the world's nicest person, she's a genuine heroine.
* BootsOfToughness: She wears boots most of the time and is a huge badass.
* BootstrappedLeitmotif: She has her own leitmotif, which plays during her introduction, during the chase sequences, and during her boss fight. However, the Ruins leitmotif is more associated with her, playing throughout the Waterfall zone and during her boss fight. The Ruins leitmotif even plays during her death sequence (a clipped version of "An Ending"), her transformation into Undyne the Undying ("But the Earth Refused to Die"), and the battle against Undyne the Undying ("Battle Against a True Hero"), while her leitmotif is absent from those songs.
* BreakTheHaughty: She comes into battle composed and determined, fully expecting to win the battle effortlessly... but as the battle goes on, she becomes more and more frustrated at your refusal to die, eventually going from her standard smiling expression to an upset grimace. Her flavor text at this point states that she's hyperventilating, twitching her eye, and wondering if you surviving this long is a prank. And when you save her life by pouring water on her, it's implied her pride is severely damaged by the fact she was just about to die of something as mundane as overheating and was saved by someone she was doggedly trying to kill, making her re-examine going after you. However, she'll still end up on bitter terms with you unless you've played as a complete pacifist ''and'' hung out with her.
* ButchLesbian: HotBlooded, an ActionGirl, refuses to do anything by halves... about the only reason she's not under TestosteronePoisoning is that she's female, and yep, she likes the ladies.
* CatSmile: After befriending her on a pacifist run, she usually wears one whenever Alphys comes up in a conversation.
* ChallengeSeeker: Tell her she can't do something. Anything at all. She will do exactly what you say she can't do, or die trying! For example: when she resists befriending you, Papyrus uses ReversePsychology on her, saying she's "not up to the challenge". After that, she insists on becoming "besties" with you.
* ClimaxBoss: She's the boss of a backstory-heavy level, and marks the point at which the player stops moving forward and begins [[ItsAllUpstairsFromHere advancing toward the surface]]. This is also the point at which the ramifications of the player's actions are made explicit: on the Neutral route, she'll call the player out for killing Papyrus or any other enemy; on the Pacifist route, she'll mock the player for being a goody two-shoes; and on the No Mercy route, she'll realize the player's out to kill ''the entire world'', human and monster alike, transform into Undyne the Undying, and claim that the player will succumb to everyone's hopes and dreams.
* CommanderContrarian: When you finally fight Undyne, she'll be angry regardless of how you played: if you killed Toriel and/or some minor monsters, Undyne will say she thought humans were compassionate, but you're just a monster. If you killed Papyrus, she'll specifically call you out on it. And if you played as a pacifist, Undyne will say she thought humans were cool, but you're just a wimp and also assume it's just an act. In truth, Undyne doesn't want to face the [[MoralDilemma implications]] of murdering a child to save the Underground, so she just comes up with a reason for them to deserve to die anyway.
* ContraltoOfDanger: Her VoiceGrunting is among the deepest in the game, implying she has one of these.
* CoolBigSis: According to their nicknames, Undyne is probably 3-4 years older than Papyrus, and he seems to view her as something like this. She in turn is very protective of him, and it's obvious that despite their bickering she cares about Papyrus a lot.
* CowardlyBoss: Inverted. To defeat her peacefully, you have to flee battle and then run away as far as you can before she catches up and continues attacking until she can't go any further.
* CulturedBadass: Plays a snippet of Alphys' theme on the piano fairly well, from what little you can hear of it. Can make good tea, though the rest of her culinary skills are questionable. She also ''thinks'' she's well-versed in human history through no fault of her own, making her an incidental PopCulturedBadass.
* DarthVaderClone: Subverted, she's made out to be one when you first see her in her dark armor and menacing nature. However, she soon turns out to be quite different.
* DeathByIrony: A possible case, depending on the player. Undyne refuses to let Papyrus into the Royal Guard because she believes that his general innocence and unwillingness to kill would make him ineffective at best and put him in danger at worst. But Papyrus' total lack of malicious intent can make him so endearing that even capable players might refuse to harm him purely on principle. By contrast, not only is the method used to spare Undyne unintuitive, her attitude and actions can prompt less forgiving players not to even bother.
* DefiantToTheEnd:
** If she's slain on a No Mercy run, she'll just smile proudly (while in anguish) and proclaim that she allowed for others to escape and that King Asgore will avenge her.
** If she's slain on a Neutral run, she'll continue fighting even when her HP bar is depleted. But as you keep beating her down, her body breaks down and her attacks slow to a crawl, and goodness, ''the music''... She keeps refusing to die, but her body can't take it anymore, and melts before turning to dust.
** Just before the final battle of a True Pacifist run, [[spoiler:after everyone's captured by Flowey's vines, she's visibly struggling against hers.]]
* TheDeterminator: Undyne is extremely tenacious, regardless of how your approach her. Particularly if you choose to Fight her or take the No Mercy route. 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.
* EasilyForgiven:
** Notably averted. Unlike most monsters, who will act neutral or amiable to you no matter how many monsters you've killed, Undyne dislikes humans to begin with and refuses to forgive even a single monster's death at your hands. That said, it's possible to befriend her and (kind of) change her mind if you haven't hurt a soul.
** She is on the receiving end of the trope if the protagonist does [[AllLovingHero befriend]] her, as she is unquestionably the most hostile monster you meet, tries to kill you not one, but several times, and is one of the very rare monsters who '''cannot''' be directly talked out of battling you.
* EstablishingCharacterMoment: The cutscene right before her boss fight in a Neutral/Pacifist run. Up until now, her actions and dialogue had made her seem like the standard BlackKnight archetype: serious, cold, and direct in her efforts to stop the player. Then she suddenly tears off her helmet and goes on a really hammy rant about why the player's existence is a detriment to all monsterkind and how she'll do anything to protect them, all while her real {{Leitmotif}} -- a heroic and somewhat goofy-sounding theme -- plays in the background.
* EveryoneHasStandards:
** Apparently, she won't fight someone who's on the phone. During the middle of the fight in the Neutral/Pacifist run when Papyrus calls you, she won't attack while you're talking to him. This isn't a matter of TalkingIsAFreeAction -- if you speak with Undyne in the same room after befriending her, she'll say she had to wait because you had a phone call.
** She also insists on making sure the fight is a fair one -- if you fail to block her first attack, she'll remind you how the mechanic works, and if you keep failing, she'll complain that she gave you a spear to block with just to make things fair and become quite frustrated.
** She also believes in SacredHospitality, so as much as she loathes you at the time, she won't attack you while you're at her house (with the exception of the "rematch" that gets triggered if you ARE on good terms with her).
* EyeBeams: Upon transforming into Undyne the Undying, she gains the ability to shoot energy out of the eye that had been covered by her eye patch.
* EyeColourChange: When she taps into her Determination, her sclera turn black and her pupils white. It only happens after she's mortally wounded in a Neutral or No Mercy run.
* EyepatchOfPower: Most people will barely notice that she wears one. And it's not for nothing either, as she is missing that eye. [[spoiler:Subverted in a No Mercy run, where she loses it as Undyne the Undying]].
* FantasticRacism: She has a rather odd love-hate relationship with humans. While it's clear she thinks very little of them, she also watches a lot of "human history" (read: anime) with Alphys, and it's clear that it's an influence in her demeanor. She also mellows her demeanor toward humans on a pacifist run, and on No Mercy, she realizes that you're just as much a threat to humans as you are to monsters and fights for them as well.
* FieryRedhead: She's a HotBlooded LargeHam, and her overworld sprite reveals that she's got a big red ponytail under that helmet.
* FishPeople: Looks like a fish when she takes her armor off. Her online handle is [="StrongFish91".=]
* FriendToAllChildren: She apparently knows the children that live in Snowdin Woods on a personal basis.
* {{Gaydar}}: Amusingly enough, subverted. Despite being a lesbian herself, she is completely clueless to the obvious UST between two of her male subordinates. Even if they hook up (with the player's help), she still seems to think they have a close, platonic friendship.
* GetBackHereBoss: Inverted by Undyne -- if you want to overcome her non-lethally, you'll be the one doing the fleeing, while Undyne shouts at you to hold still so she can kill you.
* GettingHotInHere: Something similar happens to Undyne in the Pacifist or Neutral Route. You run away from her and lead her to Hotland, which has the same effect, but instead of taking her armor off, she collapses from [[ThirstyDesert dehydration]]. Giving her a glass of water revives her and gets her to leave you alone.
* GlassCannon: Statistically, anyways. She has a very powerful attack score of seven, but her defense score is '''''zero''''', despite all of that heavy armor she's wearing. She has enough health to make up for it, though. Averted during a No Mercy route, as she's one of the few things that can take more than one hit from you.
* GoOutWithASmile: On the No Mercy route, she dies happy believing that her friends will stop you from killing everyone after her death.
* HandicappedBadass: Sometimes players forget she is missing an eye.
* HelmetsAreHardlyHeroic: She's wearing a full helm in her first appearance, but ditches it right before she is fought and never wears it again.
* HeroAntagonist: Begins this way, but can get over it in the pacifist endings.
* HeroicBSOD: In most neutral endings where she's alive, Undyne either swears vengeance on you or forgives you, depending on your friendship with her. However, if your neutral run ends with Asgore and Mettaton dead, Papyrus explains that Alphys vanished. As a result of losing both Asgore ''and'' Alphys, Undyne completely gives up at life, spending most of her time either working at Sans's hotdog stand or laying on his couch.
* HeroicRROD: In the No Mercy run, she has so much determination and willpower to strike you down in order to save her homeland [[spoiler:that energy radiates out of her eye socket where her eyepatch was, and then her body begins to ''melt'' before disintegrating (a side-effect of monsters with determination, as Alphys is all too aware of)]].
* HeroicSecondWind: If you kill her during the neutral route, she shows signs of pulling this, but it turns out to be a mere HopeSpot. During the No Mercy route, however, after taking a killing blow directed at Monster Kid, she manages to come back even stronger than before. In both situations, she finally dies when she begins to melt, meaning she had SO MUCH willpower, she was creating her own Determination.
* HeroWorshipper: She seemed to be this in her youth for Gerson, the old turtle archeologist (who was once a hero himself). That relationship wasn't much unlike the current relationship between her and the Monster Kid, as she was also described as being clumsy back then.
* HiddenDepths: The version of Undyne most people see is a HotBlooded anime-loving BloodKnight. Then there's a layer on which she is insightful, gentle, and caring. She admires Asgore for his pacifism, doesn't want to let Papyrus in the Royal Guard despite his fighting skills because of his naivete and kindness, and is in love with Alphys for her passion. She won't hurt an innocent... except the protagonist on a Pacifist run, which is a source of great conflict to her. The strange behavior on the date with her just highlights how much of a MoralDilemma she's been facing with the apparent salvation of monsterkind being killing a kid.
* HonorBeforeReason: Despite wanting your soul, Undyne, during the fight with you. gives you a spear and allows you to save, rather than simply capturing you and bringing you to the King. She's emulating all the anime she's watched.
* HotBlooded: Does absurd things like ''suplex boulders'' in the middle of a fight, just because she can. Even her cooking is hot-blooded, making spaghetti sauce by punching the vegetables, and stirring the pot by stabbing it with her spear.
* InsultToRocks: Even with her disdain for humans, when she fights you in No Mercy, one of the lines she uses is "Human... no. ''Whatever'' you are...", which seems to have a taste of this to it; she regards you as being even more contemptuous than humans in general, and that's saying a lot.
* InterfaceScrew: When your soul is green during her fight, sometimes the next bullet to hit you will be highlighted red. ...Sometimes it won't.
* {{Irony}}: She's a HotBlooded BadassGay ScreamingWarrior who also plays the piano...an instrument whose name means "soft" or "quiet" in musical notation.
* JerkWithAHeartOfGold:
** ''Very much so''. She's extremely aggressive, but also completely dedicated to justice for all of monster-kind. This trope can be seen in full effect whenever she shows "affection" toward the people she likes.
** She will lambast a Pacifist player for being a wimp and a coward. However, killing even ONE monster will preclude any chance of friendship with her.
* KnightOfCerebus: Subverted. She's the first boss character in the game who wishes to ''kill'' you, marking a turning point for the tone of the game, and gets quite a lot of build up as someone the human child shouldn't mess with. After you meet her, however, she drops the silent, stoic facade, revealing she's just as prone to the bizarre antics as a lot of the rest of the cast.
* KnightInShiningArmor: Ironically, despite fitting all the criteria for a BlackKnight she has the personalty and moral code of this trope. While she is out to kill you it is purely to free her people and even then she's not exactly happy about it. Further, if you become the Villain, then Undyne will be the Heroine that stands in your way. She's even acknowledged as such in game.
* TheLadette: She shows traits of being one, anyway. Loud, rude, loves fighting with a passion... And then there's her tendency to involve [[ToiletHumor projectile vomiting]] in her puzzle ideas.
* LargeHam: Does everything (aside from crafting puzzles) with EXTREME ardor, from making friends to cooking.
--> '''Undyne''': CHERISH HARDER!
* {{Leitmotif}}: At first, "Undyne." After she unmasks herself, it's replaced by "NGAHHH!!"/"Spear of Justice." As the Undying, she gets "Battle Against a True Hero" as her battle theme.
* LethalChef: Suffice to say, one cooking lesson from her will highlight where Papyrus gets his "skills" from.
-->'''Undyne''': ''(After setting fire to her kitchen)'' Ah. Man, no wonder Papyrus sucks at cooking.
* LetsFightLikeGentlemen: She wants to defeat you fairly, so she gives you a spear at the beginning of the battle to block her attacks. If you repeatedly fail to block her first attack, she gets extremely pissed off over you being such a worthless opponent, and unleashes an extremely brutal flurry of attacks.
* LikeBrotherAndSister: Her relationship with Papyrus falls squarely into this.
* LogicalWeakness: A water dweller wearing full plate armor that heats up easily? Of course she doesn't do too hot in a volcano area...
* LonelyPianoPiece:
** In a neutral run, a clipped version of "An Ending" plays once you have depleted Undyne's health, but before she dies. This hammers in the fact that she is going to die, no matter how hard she tries to pull herself back together with Determination.
** On a No Mercy run, the triumphant "Battle Against a True Hero" plays. It has a piano segment that sounds like a feeling of hope that is false.
* MakingASplash: The spears that she summons appear to be made of water.
* MamaBear: If you have killed Papyrus on a neutral run, [[OOCIsSeriousBusiness Undyne becomes incredibly cold and straightforward]]. No heroic declarations, not even the hamminess she has on No Mercy, nothing but quiet rage. And, with no shouting or theatrics whatsoever, so swears that she will ''kill'' you.
* MasculineGirlFeminineBoy: The Masculine Girl to Papyrus' Feminine Boy.
* MeaningfulName: An [[https://en.wikipedia.org/wiki/Undine undine]] is a female water spirit. Undyne is a FishPerson that can conjure spears made from water. Also comes up in the Genocide Route -- Undyne the ''Undying''. An undine's goal is to obtain an immortal soul, and Undyne's goal is to obtain the player's SOUL.
* MonsterKnight: Quite literally. She is a monster, and a knight, and she has the sense of honor and justice that comes with the description.
* MoralDilemma: Being a chivalrous fighter, Undyne has some doubt about the righteousness of killing a child to save monsterkind. She doesn't own up to this unless she's befriended, however, and will come up with varying "reasons" that necessitate your death. Depending on your behavior up to this point, her reasons for attacking you range from entirely justified and correct (if you've been violent up to that point, even on a Neutral run), to a note of ItsPersonal (if you've killed Papyrus on a Neutral run), to grasping at straws (if you've been entirely pacifistic).
* MusclesAreMeaningless: She's surprisingly skinny underneath all that armor, and she suplexes boulders![[note]]Because she can![[/note]]
* NonMammalMammaries: When she is out of her armor, she has a visible, albeit small, bust.
* NoSell: She's so determined to capture you that even the debug command that makes monsters instantly spareable doesn't work on her.
* NoSocialSkills: The two of you hanging out starts with her breaking her table in half with her spear when you try to select a beverage, and ends with the two of you accidentally burning her house down while trying to make spaghetti.
* NotInFrontOfTheKid: One phone call with her has her cutting herself off before she says the word "ass" to you and substituting the word "booty" instead.
* NotSoAboveItAll:
** Although she seems like a very straight-laced, dutiful knight fitting her position as head of the Royal Guard, once you befriend her, it turns out she's just as big of an enthusiastic goofball as Papyrus himself. The monologue she subjected you to just before her fight was something she'd [[RuleOfCool been practicing for just the occasion,]] and the reason she cut it off partway through was because ''she forgot the rest of it.''
** Possibly shown later when you question her about the soda in her house. She claims to not like it because it's "gross" and "it rots your fighting spirit", but she responds with an embarrassed silence when you ask her why she even has it if she doesn't like it. It's either an example of this or, considering [[CatSmile the look on]] [[LuminescentBlush her face]], it's also possible that she keeps it for Alphys.
* OfficialCouple: [[spoiler:Becomes this with Alphys in the true ending route.]]
* OneNoteCook: Her overexuberance leads to disaster when she cooks, but her tea is specifically noted to be good, though too hot to drink properly when you first get it.
* OneWingedAngel: As Undyne the Undying. Her attacks get more complex, deal far more damage, and move much faster. She also switches the player's SOUL color between red and green more often, and the player is prevented from escaping the fight.
* OOCIsSeriousBusiness: Undyne if you, kill Papyrus but aren't on a No Mercy route. Once you reach the area you must fight her there are no cheesy speeches, no flashy intros, nothing but sheer, silent, hatred towards you.
--> '''Undyne''': ''What did you do to him? What did you DO TO HIM?''
* PerpetualSmiler: Once the helmet's off, she almost never frowns. Due to her large teeth this can border on a SlasherSmile at times, but it is also strangely endearing. [[spoiler:Reminding her of how much she loves to smile is one of the ways you can Act when facing her as a Lost Soul.]]
* PlatonicLifePartners: She's huge friends with Papyrus, but they're clearly only friends, and it's enforced by the fact that Undyne's a lesbian.
* PlayingWithFire: Examining her stovetop during the Child's visit to her house will prompt Undyne to remark that despite the wonders of technology, flame magic-cooked food beats the stove when it comes down to it, so she might have access to such magic. Regardless, she pulls this trope literally, cranking the heat up on the stove to needless levels and promptly burns her house down when it explodes in her face.
* PowerIncontinence: In her normal boss battle, once you deplete her HP, she lingers around, requiring a few more attacks to fully defeat her. While this happens, her body begins wavering in and out of focus. Her will to stay alive is strong enough to generate Determination, but without the realization that you are a threat to the entire world giving her the final push, she simply can't muster enough of it to stave off death. The result is only a partial transformation (her visible eye's colors invert) and she begins to melt before disintegrating into dust.
* ThePowerOfFriendship: Professes this to cheesy anime levels.
* PunnyName: Undines are mythological elemental creatures of water. Undyne is a fish looking monster who lives in a house that also looks like a fish. It's also a play on "Undying", which comes into play when you fight her on a Genocide route.
%%* RedOniBlueOni: Red oni to Alphys' blue oni.
* RightForTheWrongReasons: When you fight her after having killed people, she'll call you a cold-blooded murderer and immediately reject your protests of self-defense by saying "You didn't kill them because you had to. You did it because it was ''easy''". She is somewhat correct, as the player can reload saves as much as they want and thus arguably has no excuse but to strive for the perfect nonviolent outcome. However, [[BlueAndOrangeMorality how exactly she came to this conclusion]] ''without'' knowing about the fourth wall [[InsaneTrollLogic is anyone's guess]].
* SacredHospitality: Sure, she's antagonistic with you until her house gets burned down, but ''you're not going to get up for '''anything''' as long as you're a guest in HER house.''
* SamusIsAGirl: She wears a huge, feature-obscuring suit of armor, but many people refer to her as a woman before you see what she actually looks like.
* SeriousBusiness: Exploited when befriended. When Papyrus tries to set up the player and her as friends, she refuses. Papyrus plays it up as a challenge, she does it for the need to win.
* SheWhoFightsMonsters: She's so determined to get another soul for Asgore that she's willing to [[WouldHurtAChild kill a child]] to get one, making her just as bad -- if not ''worse'' (No one can say for certain if during the war, humans killed monster children) -- than the people who locked her people underground.
* ShootTheShaggyDog:
** She was only trying to keep the world safe...[[YouBastard from YOU.]]
** Furthermore, on a No Mercy run, she's confident that Asgore will avenge her. [[spoiler:He puts up even ''less'' of a fight than [[strike:Undyne]] '''[[ZeroEffortBoss Mettaton NEO]]''' when you face him later on.]]
* SignatureScent: "Smells like sushi" and "smells like angry fish" will occasionally pop up in her battle.
* SirSwearsALot: The level of language in ''Undertale'' is pretty conservative to begin with, but Undyne is the most crassly-spoken among the cast.
* StatuesqueStunner: She's among the tallest of the characters, only after Asgore, Mettaton, and Toriel.
* StealthPun: She's a kind of fish-monster who fights using spears. A '''''spearfish'''''.
* TheStoic: When she stalks you she is completely silent, and never says a word. Eventually, she gets sick of your shit and [[NotSoStoic starts behaving like an overly hammy anime heroine]]. The latter is what sticks for the rest of the game.
* StraightGay: Aside from the occasional ShipTease, the only way to get a clear hint of her lesbianism is if you try calling her from the garbage dump, where she talks about how it's "a good place to pick up chicks", with a clear air of personal experience. And the only way to confirm it is by playing the Pacifist route, where she eventually recruits you to help win Alphys' heart.
* TacticalSuicideBoss: Well, not exactly suicide. During the battle, she can smack your SOUL with her spear to switch it from green to red and vice versa. She intends for this to allow her to use a second attack pattern, but she forgets something; the red SOUL has the ability to run from battle.
* TakeAThirdOption: If you successfully befriend her, she finds a loophole in her MoralDilemma: spare you and wait for a [[AssholeVictim genuinely awful human being that actually deserves it to fall into the Underground and kill them for the final SOUL instead.]]
* TakingTheBullet: On a No Mercy round, Undyne takes the bullet for the Monster Kid when the player attempts to kill the Kid. This allows her to turn into Undyne the Undying moments later.
* TalkingDownTheSuicidal: Her first meeting with Dr. Alphys was at the bottomless abyss in Waterfall's garbage dump, where Alphys was staring into the depths, looking "contemplative." She asked Alphys where she thought the abyss led to. Cue ''several hours'' of Alphys running through every theory she had almost without stopping, leaving Undyne captivated. In the end, Undyne managed to talk Alphys out of committing suicide [[{{Irony}} without having to say much at all]].
* TankTopTomboy: When she's out of her armor, she's usually in a black tank top.
* TechnicallyASmile: She tends to show these when her plans derail or something unexpected happens. During the first third of your time hanging out with her, she shows one constantly which makes her, as you know what she is capable of, extremely scary as you are constantly afraid that she will impale you with a spear.
* {{Teleportation}}: She seems to have some sort of teleportation ability -- notice how she just vanishes into the darkness with a "magical" sound effect after you first see her. She doesn't use it nearly as liberally as Sans, though.
* ThisIsUnforgivable: Won't befriend you if you've killed any monsters beforehand (and explicitly mentions if Papyrus doesn't show up to his meeting with her...), and killing anyone after befriending her will cause her to hate you far more in the ending phone call than she would if you had just killed people.
* TinTyrant: In her first appearances, her body is fully covered in platemail, so her face doesn't show. She even makes a heavy clanging sound when she walks. [[HelmetsAreHardlyHeroic She discards the helmet when she battles you]].
* ToiletHumor: Loves this. Particularly notable is her puzzle idea of "timing pukes."
* {{Tomboy}}: She partakes in male-oriented activities and has all the masculine gender roles you can think of.
* TomboyAndGirlyGirl: Tomboy to Alphys' girly girl.
* TomboyishVoice: Her deep VoiceGrunting implies that she has this.
* TookALevelInBadass: Not that she wasn't badass before, mind you, but in a No Mercy run, she takes '''several''' levels when she becomes Undyne the Undying. [[WakeUpCallBoss And we do mean "several".]]
* TranquilFury:
** If you kill Papyrus on a Neutral run, she slips into this.
** Even as Undyne the Undying, she falls into this. After her HotBlooded speech about how she can feel everyone's hearts beating as one, she becomes completely quiet for as long as the battle goes on, focusing entirely on killing you.
* {{Troll}}: Has a tendency to do this, especially on Papyrus.
-->'''Papyrus''': OH MY GOD??? NO? WHY??? I THOUGHT YOU HATE MAKING PUZZLES!!\\
'''Undyne''': Yeah, but I love driving you crazy!
* {{Tsundere}}: She acts extremely aggressive in order to cover up her softer side. The "dere" side is mostly reserved for Alphys. She also shows some of her softer side with Papyrus, though platonically.
* TVNeverLies: Watching [[CargoCult "human history"]] with Alphys has left her convinced that anime is real.
* VoiceGrunting: Not a particularly unique sound, but she has the second deepest 'voice' in the game. Gains a subtle [[PowerEchoes reverb effect]] as Undyne the Undying.
* WakeUpCallBoss:
** She's the first enemy you see that's actively trying to kill you, and it shows! She's much more difficult to deal with than Toriel and Papyrus. The method of sparing her is quite unorthodox as well. That is to say, you ''can't'' spare her. You run away.
** She's also this if you're attempting a No Mercy run. Players expecting her to get one-shot like every other enemy in a No Mercy run are going to be in for one ''hell'' of a surprise.
* WasItAllALie: In the True Pacifist playthrough. [[PlayedForLaughs She laughs off Alphys' confession that anime is fiction... but as soon as Alphys is out of earshot she begins to undergo an existential crisis.]]
* WhyWontYouDie: As the battle drags on, she gets progressively more angry at the fact that you're able to survive her attacks, eventually reaching a point where she abandons her main attack pattern and just starts hurling spears around. This is the best time to start running from her, as she'll never turn your SOUL back to green.
-->'''Undyne:''' NGAHHH!!! DIE ALREADY, YOU LITTLE BRAT! I WILL NEVER TAKE MERCY FROM THE LIKES OF YOU! YOU! WILL! NEVER! SPARE! ME!
* WrongGenreSavvy:
** After Alphys tells her that anime and comic books are "human history," she's become convinced that the world works that way. As a result, she acts much like a typical {{shonen}} anime protagonist.
** In a No Mercy mode, she's more or less correct. She really is a genuine hero, powered by ThePowerOfFriendship and sheer determination, fighting to prevent the world's destruction. The only thing she's wrong about is that the hero always succeeds... That said, the battle is so brutal that it makes some players give up on the run altogether, so her cause is not so hopeless after all.
* YouAreACreditToYourRace: She has a grudging respect for "human culture". It's implied she eventually feels this way about a Pacifist protagonist, [[spoiler:as when she's saved from being a Lost Soul she mentions ''some'' humans are alright.]]
* YouAreWhatYouHate: Aside from being influenced by human anime, she possesses a number of attributes that are described in-game as belonging to humans, such as a strong will to kill and implicitly, Determination.
* YouBastard:
** On a neutral run, her opening speech calls you out for particular monsters that you've slain. ''Especially'' Papyrus.
** If you abandon a pacifist run by killing someone after befriending her, Papyrus notes in the epilogue that Undyne took your betrayal of her belief in you ''very'' harshly, and that if you ever returned to the underground, nothing, would be able to stop her from killing you. The only exception is if the "one enemy" is Metatton; [[spoiler:since it causes Alphys to commit suicide]], it leaves her in a full blown HeroicBSOD.
[[caption-width-right:204: [[TheDeterminator NGAHHH!!!]]]]
[[caption-width-right:262:Click [[labelnote:here]]http://static.tvtropes.org/pmwiki/pub/images/the_undying.png[[/labelnote]] to see her Genocide run form.]]
The captain and commander of the Royal Guard that protects the underground. Likes spears. Dislikes humans. [[BreadEggsBreadedEggs Likes throwing spears at humans.]]
----
* ActionGirl: Loves fighting and big swords. What else could she be? But try to hurt her friends, and...
* {{Adorkable}}: No, really. It's downplayed, but it is there, as she genuinely believes that anime is real.
* AffectionateParody: Everything about her seems to be one to common shonen and shojo anime tropes. She appears to be wearing [[Franchise/DragonBall Saiyan armor]]. She even has a transformation involving the hearts of everyone in the world uniting to defeat you on the No Mercy route.
* AmbidextrousSprite: Her overworld sprite is mirrored and leaves a glaring mistake. When walking to the left, Undyne doesn't have her eyepatch on.
* AngstWhatAngst: She doesn't seem even ''slightly'' perturbed when she accidentally burns her house down, and the whole situation is PlayedForLaughs. 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.
%%* AntiVillain
* ArcVillain: Of Waterfall, in the same way that Mettaton is the arc villain of Hotland. Throughout Waterfall, a fairly backstory-heavy level, you're constantly pursued by Undyne, who is intent on killing you, regardless of how you've acted up until this point. Her battle marks the point where you start making great strides towards returning to the surface. Undyne could also be viewed as this to Snowdin, since Papyrus is a total non-threat -- it's wanting to please ''Undyne'' that drives him to fight you.
* ArmorIsUseless: She has negative defense in her boss fight, despite being covered in plate. During her un-armored rematch after the "date", she somehow has more defense.
* AsskickingEqualsAuthority: Until you encounter Undyne, the only members of the Royal Guard you've seen are five silly dogs that can be gotten past by petting. When Undyne shows up, she makes it very clear that she's the leader of the guards for a reason. Depending on your actions in the Underground, she might decide that Toriel (who's hardly a push-over herself) is too soft-hearted to become Queen after Asgore's death, and will successfully usurp the throne from her.
* BadassGay: She's a really tough woman. She also has a thing for Alphys, and asks you to deliver a love letter she wrote to her in the true ending route, because she can't muster the courage to do so herself. And if you call her while in the garbage dump, she'll describe it as "a GREAT place to meet girls."
* BatmanGambit: Records a message on an Echo Flower telling the human to look behind them so she can set up a dramatic ambush. [[spoiler:This flops when Monster Kid shows up.]]
* {{BFS}}: Though Undyne prefers using spears in battle, she keeps a giant sword in her house. Since she believes anime is true, she thinks humans historically have wielded swords up to ten times their size.
* BladeOnAStick: Her weapons are spears, and she seems to be able to summon and throw as many as she wants, often throwing 3 at once or summoning up to 6 through the floor. While they appear to be made of water in the overworld, her battle sprites seem to be holding whole spears.
* BlackKnight: In her first appearances. Her dark armor covers her entire body, disguising her face. She is almost never heard speaking, giving her a very sinister and mysterious vibe. Naturally, she is incredibly powerful and a major antagonist (being TheDeterminator that relentlessly chases you through the whole Waterfall zone). Unusually, she uses spears instead of swords.
* BloodKnight: Loves fighting. In fact, it's impossible to spare her when you engage in combat -- you have to run away, as she refuses to accept your mercy.
* BlueIsHeroic: Her skin is blue, and while she's not the world's nicest person, she's a genuine heroine.
* BootsOfToughness: She wears boots most of the time and is a huge badass.
* BootstrappedLeitmotif: She has her own leitmotif, which plays during her introduction, during the chase sequences, and during her boss fight. However, the Ruins leitmotif is more associated with her, playing throughout the Waterfall zone and during her boss fight. The Ruins leitmotif even plays during her death sequence (a clipped version of "An Ending"), her transformation into Undyne the Undying ("But the Earth Refused to Die"), and the battle against Undyne the Undying ("Battle Against a True Hero"), while her leitmotif is absent from those songs.
* BreakTheHaughty: She comes into battle composed and determined, fully expecting to win the battle effortlessly... but as the battle goes on, she becomes more and more frustrated at your refusal to die, eventually going from her standard smiling expression to an upset grimace. Her flavor text at this point states that she's hyperventilating, twitching her eye, and wondering if you surviving this long is a prank. And when you save her life by pouring water on her, it's implied her pride is severely damaged by the fact she was just about to die of something as mundane as overheating and was saved by someone she was doggedly trying to kill, making her re-examine going after you. However, she'll still end up on bitter terms with you unless you've played as a complete pacifist ''and'' hung out with her.
* ButchLesbian: HotBlooded, an ActionGirl, refuses to do anything by halves... about the only reason she's not under TestosteronePoisoning is that she's female, and yep, she likes the ladies.
* CatSmile: After befriending her on a pacifist run, she usually wears one whenever Alphys comes up in a conversation.
* ChallengeSeeker: Tell her she can't do something. Anything at all. She will do exactly what you say she can't do, or die trying! For example: when she resists befriending you, Papyrus uses ReversePsychology on her, saying she's "not up to the challenge". After that, she insists on becoming "besties" with you.
* ClimaxBoss: She's the boss of a backstory-heavy level, and marks the point at which the player stops moving forward and begins [[ItsAllUpstairsFromHere advancing toward the surface]]. This is also the point at which the ramifications of the player's actions are made explicit: on the Neutral route, she'll call the player out for killing Papyrus or any other enemy; on the Pacifist route, she'll mock the player for being a goody two-shoes; and on the No Mercy route, she'll realize the player's out to kill ''the entire world'', human and monster alike, transform into Undyne the Undying, and claim that the player will succumb to everyone's hopes and dreams.
* CommanderContrarian: When you finally fight Undyne, she'll be angry regardless of how you played: if you killed Toriel and/or some minor monsters, Undyne will say she thought humans were compassionate, but you're just a monster. If you killed Papyrus, she'll specifically call you out on it. And if you played as a pacifist, Undyne will say she thought humans were cool, but you're just a wimp and also assume it's just an act. In truth, Undyne doesn't want to face the [[MoralDilemma implications]] of murdering a child to save the Underground, so she just comes up with a reason for them to deserve to die anyway.
* ContraltoOfDanger: Her VoiceGrunting is among the deepest in the game, implying she has one of these.
* CoolBigSis: According to their nicknames, Undyne is probably 3-4 years older than Papyrus, and he seems to view her as something like this. She in turn is very protective of him, and it's obvious that despite their bickering she cares about Papyrus a lot.
* CowardlyBoss: Inverted. To defeat her peacefully, you have to flee battle and then run away as far as you can before she catches up and continues attacking until she can't go any further.
* CulturedBadass: Plays a snippet of Alphys' theme on the piano fairly well, from what little you can hear of it. Can make good tea, though the rest of her culinary skills are questionable. She also ''thinks'' she's well-versed in human history through no fault of her own, making her an incidental PopCulturedBadass.
* DarthVaderClone: Subverted, she's made out to be one when you first see her in her dark armor and menacing nature. However, she soon turns out to be quite different.
* DeathByIrony: A possible case, depending on the player. Undyne refuses to let Papyrus into the Royal Guard because she believes that his general innocence and unwillingness to kill would make him ineffective at best and put him in danger at worst. But Papyrus' total lack of malicious intent can make him so endearing that even capable players might refuse to harm him purely on principle. By contrast, not only is the method used to spare Undyne unintuitive, her attitude and actions can prompt less forgiving players not to even bother.
* DefiantToTheEnd:
** If she's slain on a No Mercy run, she'll just smile proudly (while in anguish) and proclaim that she allowed for others to escape and that King Asgore will avenge her.
** If she's slain on a Neutral run, she'll continue fighting even when her HP bar is depleted. But as you keep beating her down, her body breaks down and her attacks slow to a crawl, and goodness, ''the music''... She keeps refusing to die, but her body can't take it anymore, and melts before turning to dust.
** Just before the final battle of a True Pacifist run, [[spoiler:after everyone's captured by Flowey's vines, she's visibly struggling against hers.]]
* TheDeterminator: Undyne is extremely tenacious, regardless of how your approach her. Particularly if you choose to Fight her or take the No Mercy route. 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.
* EasilyForgiven:
** Notably averted. Unlike most monsters, who will act neutral or amiable to you no matter how many monsters you've killed, Undyne dislikes humans to begin with and refuses to forgive even a single monster's death at your hands. That said, it's possible to befriend her and (kind of) change her mind if you haven't hurt a soul.
** She is on the receiving end of the trope if the protagonist does [[AllLovingHero befriend]] her, as she is unquestionably the most hostile monster you meet, tries to kill you not one, but several times, and is one of the very rare monsters who '''cannot''' be directly talked out of battling you.
* EstablishingCharacterMoment: The cutscene right before her boss fight in a Neutral/Pacifist run. Up until now, her actions and dialogue had made her seem like the standard BlackKnight archetype: serious, cold, and direct in her efforts to stop the player. Then she suddenly tears off her helmet and goes on a really hammy rant about why the player's existence is a detriment to all monsterkind and how she'll do anything to protect them, all while her real {{Leitmotif}} -- a heroic and somewhat goofy-sounding theme -- plays in the background.
* EveryoneHasStandards:
** Apparently, she won't fight someone who's on the phone. During the middle of the fight in the Neutral/Pacifist run when Papyrus calls you, she won't attack while you're talking to him. This isn't a matter of TalkingIsAFreeAction -- if you speak with Undyne in the same room after befriending her, she'll say she had to wait because you had a phone call.
** She also insists on making sure the fight is a fair one -- if you fail to block her first attack, she'll remind you how the mechanic works, and if you keep failing, she'll complain that she gave you a spear to block with just to make things fair and become quite frustrated.
** She also believes in SacredHospitality, so as much as she loathes you at the time, she won't attack you while you're at her house (with the exception of the "rematch" that gets triggered if you ARE on good terms with her).
* EyeBeams: Upon transforming into Undyne the Undying, she gains the ability to shoot energy out of the eye that had been covered by her eye patch.
* EyeColourChange: When she taps into her Determination, her sclera turn black and her pupils white. It only happens after she's mortally wounded in a Neutral or No Mercy run.
* EyepatchOfPower: Most people will barely notice that she wears one. And it's not for nothing either, as she is missing that eye. [[spoiler:Subverted in a No Mercy run, where she loses it as Undyne the Undying]].
* FantasticRacism: She has a rather odd love-hate relationship with humans. While it's clear she thinks very little of them, she also watches a lot of "human history" (read: anime) with Alphys, and it's clear that it's an influence in her demeanor. She also mellows her demeanor toward humans on a pacifist run, and on No Mercy, she realizes that you're just as much a threat to humans as you are to monsters and fights for them as well.
* FieryRedhead: She's a HotBlooded LargeHam, and her overworld sprite reveals that she's got a big red ponytail under that helmet.
* FishPeople: Looks like a fish when she takes her armor off. Her online handle is [="StrongFish91".=]
* FriendToAllChildren: She apparently knows the children that live in Snowdin Woods on a personal basis.
* {{Gaydar}}: Amusingly enough, subverted. Despite being a lesbian herself, she is completely clueless to the obvious UST between two of her male subordinates. Even if they hook up (with the player's help), she still seems to think they have a close, platonic friendship.
* GetBackHereBoss: Inverted by Undyne -- if you want to overcome her non-lethally, you'll be the one doing the fleeing, while Undyne shouts at you to hold still so she can kill you.
* GettingHotInHere: Something similar happens to Undyne in the Pacifist or Neutral Route. You run away from her and lead her to Hotland, which has the same effect, but instead of taking her armor off, she collapses from [[ThirstyDesert dehydration]]. Giving her a glass of water revives her and gets her to leave you alone.
* GlassCannon: Statistically, anyways. She has a very powerful attack score of seven, but her defense score is '''''zero''''', despite all of that heavy armor she's wearing. She has enough health to make up for it, though. Averted during a No Mercy route, as she's one of the few things that can take more than one hit from you.
* GoOutWithASmile: On the No Mercy route, she dies happy believing that her friends will stop you from killing everyone after her death.
* HandicappedBadass: Sometimes players forget she is missing an eye.
* HelmetsAreHardlyHeroic: She's wearing a full helm in her first appearance, but ditches it right before she is fought and never wears it again.
* HeroAntagonist: Begins this way, but can get over it in the pacifist endings.
* HeroicBSOD: In most neutral endings where she's alive, Undyne either swears vengeance on you or forgives you, depending on your friendship with her. However, if your neutral run ends with Asgore and Mettaton dead, Papyrus explains that Alphys vanished. As a result of losing both Asgore ''and'' Alphys, Undyne completely gives up at life, spending most of her time either working at Sans's hotdog stand or laying on his couch.
* HeroicRROD: In the No Mercy run, she has so much determination and willpower to strike you down in order to save her homeland [[spoiler:that energy radiates out of her eye socket where her eyepatch was, and then her body begins to ''melt'' before disintegrating (a side-effect of monsters with determination, as Alphys is all too aware of)]].
* HeroicSecondWind: If you kill her during the neutral route, she shows signs of pulling this, but it turns out to be a mere HopeSpot. During the No Mercy route, however, after taking a killing blow directed at Monster Kid, she manages to come back even stronger than before. In both situations, she finally dies when she begins to melt, meaning she had SO MUCH willpower, she was creating her own Determination.
* HeroWorshipper: She seemed to be this in her youth for Gerson, the old turtle archeologist (who was once a hero himself). That relationship wasn't much unlike the current relationship between her and the Monster Kid, as she was also described as being clumsy back then.
* HiddenDepths: The version of Undyne most people see is a HotBlooded anime-loving BloodKnight. Then there's a layer on which she is insightful, gentle, and caring. She admires Asgore for his pacifism, doesn't want to let Papyrus in the Royal Guard despite his fighting skills because of his naivete and kindness, and is in love with Alphys for her passion. She won't hurt an innocent... except the protagonist on a Pacifist run, which is a source of great conflict to her. The strange behavior on the date with her just highlights how much of a MoralDilemma she's been facing with the apparent salvation of monsterkind being killing a kid.
* HonorBeforeReason: Despite wanting your soul, Undyne, during the fight with you. gives you a spear and allows you to save, rather than simply capturing you and bringing you to the King. She's emulating all the anime she's watched.
* HotBlooded: Does absurd things like ''suplex boulders'' in the middle of a fight, just because she can. Even her cooking is hot-blooded, making spaghetti sauce by punching the vegetables, and stirring the pot by stabbing it with her spear.
* InsultToRocks: Even with her disdain for humans, when she fights you in No Mercy, one of the lines she uses is "Human... no. ''Whatever'' you are...", which seems to have a taste of this to it; she regards you as being even more contemptuous than humans in general, and that's saying a lot.
* InterfaceScrew: When your soul is green during her fight, sometimes the next bullet to hit you will be highlighted red. ...Sometimes it won't.
* {{Irony}}: She's a HotBlooded BadassGay ScreamingWarrior who also plays the piano...an instrument whose name means "soft" or "quiet" in musical notation.
* JerkWithAHeartOfGold:
** ''Very much so''. She's extremely aggressive, but also completely dedicated to justice for all of monster-kind. This trope can be seen in full effect whenever she shows "affection" toward the people she likes.
** She will lambast a Pacifist player for being a wimp and a coward. However, killing even ONE monster will preclude any chance of friendship with her.
* KnightOfCerebus: Subverted. She's the first boss character in the game who wishes to ''kill'' you, marking a turning point for the tone of the game, and gets quite a lot of build up as someone the human child shouldn't mess with. After you meet her, however, she drops the silent, stoic facade, revealing she's just as prone to the bizarre antics as a lot of the rest of the cast.
* KnightInShiningArmor: Ironically, despite fitting all the criteria for a BlackKnight she has the personalty and moral code of this trope. While she is out to kill you it is purely to free her people and even then she's not exactly happy about it. Further, if you become the Villain, then Undyne will be the Heroine that stands in your way. She's even acknowledged as such in game.
* TheLadette: She shows traits of being one, anyway. Loud, rude, loves fighting with a passion... And then there's her tendency to involve [[ToiletHumor projectile vomiting]] in her puzzle ideas.
* LargeHam: Does everything (aside from crafting puzzles) with EXTREME ardor, from making friends to cooking.
--> '''Undyne''': CHERISH HARDER!
* {{Leitmotif}}: At first, "Undyne." After she unmasks herself, it's replaced by "NGAHHH!!"/"Spear of Justice." As the Undying, she gets "Battle Against a True Hero" as her battle theme.
* LethalChef: Suffice to say, one cooking lesson from her will highlight where Papyrus gets his "skills" from.
-->'''Undyne''': ''(After setting fire to her kitchen)'' Ah. Man, no wonder Papyrus sucks at cooking.
* LetsFightLikeGentlemen: She wants to defeat you fairly, so she gives you a spear at the beginning of the battle to block her attacks. If you repeatedly fail to block her first attack, she gets extremely pissed off over you being such a worthless opponent, and unleashes an extremely brutal flurry of attacks.
* LikeBrotherAndSister: Her relationship with Papyrus falls squarely into this.
* LogicalWeakness: A water dweller wearing full plate armor that heats up easily? Of course she doesn't do too hot in a volcano area...
* LonelyPianoPiece:
** In a neutral run, a clipped version of "An Ending" plays once you have depleted Undyne's health, but before she dies. This hammers in the fact that she is going to die, no matter how hard she tries to pull herself back together with Determination.
** On a No Mercy run, the triumphant "Battle Against a True Hero" plays. It has a piano segment that sounds like a feeling of hope that is false.
* MakingASplash: The spears that she summons appear to be made of water.
* MamaBear: If you have killed Papyrus on a neutral run, [[OOCIsSeriousBusiness Undyne becomes incredibly cold and straightforward]]. No heroic declarations, not even the hamminess she has on No Mercy, nothing but quiet rage. And, with no shouting or theatrics whatsoever, so swears that she will ''kill'' you.
* MasculineGirlFeminineBoy: The Masculine Girl to Papyrus' Feminine Boy.
* MeaningfulName: An [[https://en.wikipedia.org/wiki/Undine undine]] is a female water spirit. Undyne is a FishPerson that can conjure spears made from water. Also comes up in the Genocide Route -- Undyne the ''Undying''. An undine's goal is to obtain an immortal soul, and Undyne's goal is to obtain the player's SOUL.
* MonsterKnight: Quite literally. She is a monster, and a knight, and she has the sense of honor and justice that comes with the description.
* MoralDilemma: Being a chivalrous fighter, Undyne has some doubt about the righteousness of killing a child to save monsterkind. She doesn't own up to this unless she's befriended, however, and will come up with varying "reasons" that necessitate your death. Depending on your behavior up to this point, her reasons for attacking you range from entirely justified and correct (if you've been violent up to that point, even on a Neutral run), to a note of ItsPersonal (if you've killed Papyrus on a Neutral run), to grasping at straws (if you've been entirely pacifistic).
* MusclesAreMeaningless: She's surprisingly skinny underneath all that armor, and she suplexes boulders![[note]]Because she can![[/note]]
* NonMammalMammaries: When she is out of her armor, she has a visible, albeit small, bust.
* NoSell: She's so determined to capture you that even the debug command that makes monsters instantly spareable doesn't work on her.
* NoSocialSkills: The two of you hanging out starts with her breaking her table in half with her spear when you try to select a beverage, and ends with the two of you accidentally burning her house down while trying to make spaghetti.
* NotInFrontOfTheKid: One phone call with her has her cutting herself off before she says the word "ass" to you and substituting the word "booty" instead.
* NotSoAboveItAll:
** Although she seems like a very straight-laced, dutiful knight fitting her position as head of the Royal Guard, once you befriend her, it turns out she's just as big of an enthusiastic goofball as Papyrus himself. The monologue she subjected you to just before her fight was something she'd [[RuleOfCool been practicing for just the occasion,]] and the reason she cut it off partway through was because ''she forgot the rest of it.''
** Possibly shown later when you question her about the soda in her house. She claims to not like it because it's "gross" and "it rots your fighting spirit", but she responds with an embarrassed silence when you ask her why she even has it if she doesn't like it. It's either an example of this or, considering [[CatSmile the look on]] [[LuminescentBlush her face]], it's also possible that she keeps it for Alphys.
* OfficialCouple: [[spoiler:Becomes this with Alphys in the true ending route.]]
* OneNoteCook: Her overexuberance leads to disaster when she cooks, but her tea is specifically noted to be good, though too hot to drink properly when you first get it.
* OneWingedAngel: As Undyne the Undying. Her attacks get more complex, deal far more damage, and move much faster. She also switches the player's SOUL color between red and green more often, and the player is prevented from escaping the fight.
* OOCIsSeriousBusiness: Undyne if you, kill Papyrus but aren't on a No Mercy route. Once you reach the area you must fight her there are no cheesy speeches, no flashy intros, nothing but sheer, silent, hatred towards you.
--> '''Undyne''': ''What did you do to him? What did you DO TO HIM?''
* PerpetualSmiler: Once the helmet's off, she almost never frowns. Due to her large teeth this can border on a SlasherSmile at times, but it is also strangely endearing. [[spoiler:Reminding her of how much she loves to smile is one of the ways you can Act when facing her as a Lost Soul.]]
* PlatonicLifePartners: She's huge friends with Papyrus, but they're clearly only friends, and it's enforced by the fact that Undyne's a lesbian.
* PlayingWithFire: Examining her stovetop during the Child's visit to her house will prompt Undyne to remark that despite the wonders of technology, flame magic-cooked food beats the stove when it comes down to it, so she might have access to such magic. Regardless, she pulls this trope literally, cranking the heat up on the stove to needless levels and promptly burns her house down when it explodes in her face.
* PowerIncontinence: In her normal boss battle, once you deplete her HP, she lingers around, requiring a few more attacks to fully defeat her. While this happens, her body begins wavering in and out of focus. Her will to stay alive is strong enough to generate Determination, but without the realization that you are a threat to the entire world giving her the final push, she simply can't muster enough of it to stave off death. The result is only a partial transformation (her visible eye's colors invert) and she begins to melt before disintegrating into dust.
* ThePowerOfFriendship: Professes this to cheesy anime levels.
* PunnyName: Undines are mythological elemental creatures of water. Undyne is a fish looking monster who lives in a house that also looks like a fish. It's also a play on "Undying", which comes into play when you fight her on a Genocide route.
%%* RedOniBlueOni: Red oni to Alphys' blue oni.
* RightForTheWrongReasons: When you fight her after having killed people, she'll call you a cold-blooded murderer and immediately reject your protests of self-defense by saying "You didn't kill them because you had to. You did it because it was ''easy''". She is somewhat correct, as the player can reload saves as much as they want and thus arguably has no excuse but to strive for the perfect nonviolent outcome. However, [[BlueAndOrangeMorality how exactly she came to this conclusion]] ''without'' knowing about the fourth wall [[InsaneTrollLogic is anyone's guess]].
* SacredHospitality: Sure, she's antagonistic with you until her house gets burned down, but ''you're not going to get up for '''anything''' as long as you're a guest in HER house.''
* SamusIsAGirl: She wears a huge, feature-obscuring suit of armor, but many people refer to her as a woman before you see what she actually looks like.
* SeriousBusiness: Exploited when befriended. When Papyrus tries to set up the player and her as friends, she refuses. Papyrus plays it up as a challenge, she does it for the need to win.
* SheWhoFightsMonsters: She's so determined to get another soul for Asgore that she's willing to [[WouldHurtAChild kill a child]] to get one, making her just as bad -- if not ''worse'' (No one can say for certain if during the war, humans killed monster children) -- than the people who locked her people underground.
* ShootTheShaggyDog:
** She was only trying to keep the world safe...[[YouBastard from YOU.]]
** Furthermore, on a No Mercy run, she's confident that Asgore will avenge her. [[spoiler:He puts up even ''less'' of a fight than [[strike:Undyne]] '''[[ZeroEffortBoss Mettaton NEO]]''' when you face him later on.]]
* SignatureScent: "Smells like sushi" and "smells like angry fish" will occasionally pop up in her battle.
* SirSwearsALot: The level of language in ''Undertale'' is pretty conservative to begin with, but Undyne is the most crassly-spoken among the cast.
* StatuesqueStunner: She's among the tallest of the characters, only after Asgore, Mettaton, and Toriel.
* StealthPun: She's a kind of fish-monster who fights using spears. A '''''spearfish'''''.
* TheStoic: When she stalks you she is completely silent, and never says a word. Eventually, she gets sick of your shit and [[NotSoStoic starts behaving like an overly hammy anime heroine]]. The latter is what sticks for the rest of the game.
* StraightGay: Aside from the occasional ShipTease, the only way to get a clear hint of her lesbianism is if you try calling her from the garbage dump, where she talks about how it's "a good place to pick up chicks", with a clear air of personal experience. And the only way to confirm it is by playing the Pacifist route, where she eventually recruits you to help win Alphys' heart.
* TacticalSuicideBoss: Well, not exactly suicide. During the battle, she can smack your SOUL with her spear to switch it from green to red and vice versa. She intends for this to allow her to use a second attack pattern, but she forgets something; the red SOUL has the ability to run from battle.
* TakeAThirdOption: If you successfully befriend her, she finds a loophole in her MoralDilemma: spare you and wait for a [[AssholeVictim genuinely awful human being that actually deserves it to fall into the Underground and kill them for the final SOUL instead.]]
* TakingTheBullet: On a No Mercy round, Undyne takes the bullet for the Monster Kid when the player attempts to kill the Kid. This allows her to turn into Undyne the Undying moments later.
* TalkingDownTheSuicidal: Her first meeting with Dr. Alphys was at the bottomless abyss in Waterfall's garbage dump, where Alphys was staring into the depths, looking "contemplative." She asked Alphys where she thought the abyss led to. Cue ''several hours'' of Alphys running through every theory she had almost without stopping, leaving Undyne captivated. In the end, Undyne managed to talk Alphys out of committing suicide [[{{Irony}} without having to say much at all]].
* TankTopTomboy: When she's out of her armor, she's usually in a black tank top.
* TechnicallyASmile: She tends to show these when her plans derail or something unexpected happens. During the first third of your time hanging out with her, she shows one constantly which makes her, as you know what she is capable of, extremely scary as you are constantly afraid that she will impale you with a spear.
* {{Teleportation}}: She seems to have some sort of teleportation ability -- notice how she just vanishes into the darkness with a "magical" sound effect after you first see her. She doesn't use it nearly as liberally as Sans, though.
* ThisIsUnforgivable: Won't befriend you if you've killed any monsters beforehand (and explicitly mentions if Papyrus doesn't show up to his meeting with her...), and killing anyone after befriending her will cause her to hate you far more in the ending phone call than she would if you had just killed people.
* TinTyrant: In her first appearances, her body is fully covered in platemail, so her face doesn't show. She even makes a heavy clanging sound when she walks. [[HelmetsAreHardlyHeroic She discards the helmet when she battles you]].
* ToiletHumor: Loves this. Particularly notable is her puzzle idea of "timing pukes."
* {{Tomboy}}: She partakes in male-oriented activities and has all the masculine gender roles you can think of.
* TomboyAndGirlyGirl: Tomboy to Alphys' girly girl.
* TomboyishVoice: Her deep VoiceGrunting implies that she has this.
* TookALevelInBadass: Not that she wasn't badass before, mind you, but in a No Mercy run, she takes '''several''' levels when she becomes Undyne the Undying. [[WakeUpCallBoss And we do mean "several".]]
* TranquilFury:
** If you kill Papyrus on a Neutral run, she slips into this.
** Even as Undyne the Undying, she falls into this. After her HotBlooded speech about how she can feel everyone's hearts beating as one, she becomes completely quiet for as long as the battle goes on, focusing entirely on killing you.
* {{Troll}}: Has a tendency to do this, especially on Papyrus.
-->'''Papyrus''': OH MY GOD??? NO? WHY??? I THOUGHT YOU HATE MAKING PUZZLES!!\\
'''Undyne''': Yeah, but I love driving you crazy!
* {{Tsundere}}: She acts extremely aggressive in order to cover up her softer side. The "dere" side is mostly reserved for Alphys. She also shows some of her softer side with Papyrus, though platonically.
* TVNeverLies: Watching [[CargoCult "human history"]] with Alphys has left her convinced that anime is real.
* VoiceGrunting: Not a particularly unique sound, but she has the second deepest 'voice' in the game. Gains a subtle [[PowerEchoes reverb effect]] as Undyne the Undying.
* WakeUpCallBoss:
** She's the first enemy you see that's actively trying to kill you, and it shows! She's much more difficult to deal with than Toriel and Papyrus. The method of sparing her is quite unorthodox as well. That is to say, you ''can't'' spare her. You run away.
** She's also this if you're attempting a No Mercy run. Players expecting her to get one-shot like every other enemy in a No Mercy run are going to be in for one ''hell'' of a surprise.
* WasItAllALie: In the True Pacifist playthrough. [[PlayedForLaughs She laughs off Alphys' confession that anime is fiction... but as soon as Alphys is out of earshot she begins to undergo an existential crisis.]]
* WhyWontYouDie: As the battle drags on, she gets progressively more angry at the fact that you're able to survive her attacks, eventually reaching a point where she abandons her main attack pattern and just starts hurling spears around. This is the best time to start running from her, as she'll never turn your SOUL back to green.
-->'''Undyne:''' NGAHHH!!! DIE ALREADY, YOU LITTLE BRAT! I WILL NEVER TAKE MERCY FROM THE LIKES OF YOU! YOU! WILL! NEVER! SPARE! ME!
* WrongGenreSavvy:
** After Alphys tells her that anime and comic books are "human history," she's become convinced that the world works that way. As a result, she acts much like a typical {{shonen}} anime protagonist.
** In a No Mercy mode, she's more or less correct. She really is a genuine hero, powered by ThePowerOfFriendship and sheer determination, fighting to prevent the world's destruction. The only thing she's wrong about is that the hero always succeeds... That said, the battle is so brutal that it makes some players give up on the run altogether, so her cause is not so hopeless after all.
* YouAreACreditToYourRace: She has a grudging respect for "human culture". It's implied she eventually feels this way about a Pacifist protagonist, [[spoiler:as when she's saved from being a Lost Soul she mentions ''some'' humans are alright.]]
* YouAreWhatYouHate: Aside from being influenced by human anime, she possesses a number of attributes that are described in-game as belonging to humans, such as a strong will to kill and implicitly, Determination.
* YouBastard:
** On a neutral run, her opening speech calls you out for particular monsters that you've slain. ''Especially'' Papyrus.
** If you abandon a pacifist run by killing someone after befriending her, Papyrus notes in the epilogue that Undyne took your betrayal of her belief in you ''very'' harshly, and that if you ever returned to the underground, nothing, would be able to stop her from killing you. The only exception is if the "one enemy" is Metatton; [[spoiler:since it causes Alphys to commit suicide]], it leaves her in a full blown HeroicBSOD.
