Undertale Wiki
For the track named after this character, see Undyne (Soundtrack).


Undyne before her battle

Undyne (/ˈʌnˌdaɪn/ UN-dyne),[1] known as StrongFish91 on the UnderNet, is a fish-like monster that leads the Royal Guard. Clad in her full suit of armor, she pursues the protagonist through the entirety of Waterfall and is frequently evaded or inadvertently thwarted by Monster Kid.




Undyne prepares to throw her spear at the protagonist

Undyne is a piscine, anthropomorphic monster. She has blue scales and a long red ponytail. She has red and blue fins on the sides of her head, and a pair of sharp, yellow, protruding teeth. She wears a red eye shadow and has an eyepatch on her left eye. She also wears a black tank top and jeans, but debuts in armor varying in light and dark shades of gray. Her eyes have black vertical pupils and yellow sclera. Undyne has no nose.

Alphys Date

During the date with Alphys, Undyne wears a white turtleneck under a black leather jacket, a scarf around her neck, pants, lipstick, a light-colored eye patch, and lets some of her hair down.


Whenever she persists through Determination after her HP reduces to zero, her pupils turn white, and her sclera turns black. She no longer has an eyepatch, and her newly revealed empty eye socket emits a flashing light in the shape of a spear. Her hair spikes at the ends like a trident and her fin rays become more rigid and pointy. She also appears to have donned a new set of darker colored armor with souls/hearts on her chestplate and new white gloves, which have spikes protruding from their backside, accompanied by boots with pointed toes.


Undyne is passionate about everything that she does. She acts quickly on her ideas and is steadfast in her beliefs.[2] Though she wants to defeat the protagonist, she also tries to be fair and offers an explanation of how Green Mode works. Asgore taught her the value of pacifism,[3] which is why Undyne sees the protagonist as "a wimpy loser with a big heart." When the protagonist first encounters her, she fights to further Asgore's plan of collecting seven human SOULs but, if the protagonist shows mercy, Undyne just as quickly defends them from Asgore.

She loves to help others and mentors Shyren and Papyrus in various skills. Undyne dislikes puzzles, loves japes,[4] and enjoys anime, an affinity she shares with her romantic interest, Alphys. Since Alphys told Undyne that anime is actually human history, Undyne regards human history as exciting and cool.[5]

Out of all encountered monsters, Undyne possesses the most Determination. She melts before her death, implying that her body cannot handle the amount of Determination she has.

Main Story

Neutral Route

The lighting radically changes when Undyne is near

The protagonist initially encounters Undyne after entering Waterfall, where Undyne stands on top of a ledge. If alive, Papyrus approaches her and delivers a report on the status of the human, and then attempts to convince her not to harm them. After Papyrus leaves, the protagonist can continue, but the grass rustling alerts Undyne to their presence. She scopes out the grass for a moment whilst the track Undyne plays, before retreating.

Undyne follows the protagonist throughout Waterfall and repeatedly attacks them, but the protagonist always evades capture by either dodging her attacks or due to Monster Kid's interference. Later on, Undyne approaches the protagonist as Monster Kid hangs on to the side of a bridge. If the protagonist saves the Monster Kid, they protect the protagonist from Undyne. If the protagonist does not help the Monster Kid, Undyne jumps down to save them instead. Undyne takes a small amount of damage after doing this, which is useful for killing Undyne on the Neutral Route.


Undyne when enraged

After this, Undyne confronts the protagonist and stands atop a crag while giving a monologue that she has practiced many times before.[6] However, she cuts the monologue short because she forgot the rest of it[7] and launches head-on into battle.

After Undyne chases the protagonist into Hotland, she collapses due to dehydration. The protagonist can offer Undyne a glass of water, spill all the water in front of her, or continue into Hotland. If she receives water, Undyne stands up, looks around, and slowly returns to Waterfall. If the protagonist leaves this room before pouring the water, Undyne develops heatstroke and the protagonist cannot befriend her, thus preventing the True Pacifist Route requirements from being fulfilled.

True Pacifist Route

I'll make you like me so much... Your WHOLE LIFE will revolve around me!! FUHUHUHUHU!!!

Undyne during her hangout with the protagonist.

Papyrus calls the protagonist during Undyne's chase and suggests that they and Undyne should hang out at her house. If the protagonist gives Undyne water, Undyne befriends the protagonist if they have no EXP. After Undyne's battle, the protagonist can backtrack to her house and begin their hangout with her.

Undyne is initially hostile to the protagonist,[8] but changes her attitude when Papyrus presents befriending the human as a challenge. She realizes that becoming "besties" with the protagonist would be "the perfect revenge," and says that the protagonist will feel "enamored" with Undyne by the end of their hangout. Undyne discusses her training with Asgore over tea and suddenly realizes that Papyrus's cooking lesson usually occurs at this time. She insists that she and the protagonist bond over cooking, which ends in Undyne's house catching on fire. Humiliated and feeling that she failed at befriending the protagonist, Undyne battles the protagonist and offers them the first hit. Regardless on whether the protagonist deals a "fake hit" through the ACT button or a real hit through the FIGHT button, they only deal one HP of damage. Undyne realizes neither of them wants to harm one another.

Because her house scorched, Undyne moves into Papyrus and Sans's House.

After the protagonist completes a Neutral Route, they can backtrack from the CORE into the MTT Resort, and Undyne will call them to ask for a favor. In Snowdin Town, Undyne gives them a letter that she asks them to take to Alphys in Hotland. The protagonist gives Alphys the letter, but she mistakes it as being a love letter from the protagonist because it has no signature.[9] Alphys reluctantly goes on a date to the Garbage Dump with the protagonist. Alphys hides behind a trash can upon seeing Undyne, who then arrives and sees the protagonist at the dump and asks for her letter back; she wants to give it to Alphys herself. After Undyne walks away, Alphys expresses regret about her lying to Undyne, and the protagonist suggests a roleplay to help Alphys express her feelings.[10] Undyne interrupts the roleplay, and Alphys tells her about her romantic interest. Undyne reciprocates these feelings and tosses Alphys into the trashcan.[11]

Undyne says that Alphys needs to work on her self-image,[12] and Papyrus leaves with Alphys to help with her emotional transformation. After the two leave, Undyne asks the protagonist if anime is real or not and thanks them for helping with Alphys.

Later on, Undyne interrupts Asgore's encounter with the protagonist and demands that they befriend one another. Prompted by Mettaton, Alphys and Undyne almost kiss before Flowey's ambush, but Toriel chastises them for kissing in front of a child. Flowey ensnares the protagonist's friends with a Photoshop Flowey vine, and Undyne protects them from incoming attacks from Flowey. He then absorbs the six human SOULs and most of the SOULs of the monsters in the Underground.

During the battle against Asriel, Undyne appears as one of the Lost Souls.


When the protagonist talks to Undyne in the epilogue, Undyne states that she is glad that she lost to the protagonist and then resolves to watch anime with Alphys. The Royal Guard is disbanded. Toriel also texts the protagonist that Undyne was able to lift Asgore, Sans, Papyrus, Alphys, and Toriel herself at once, but was uncertain as to how to put them down.

On the surface, Undyne pursues Papyrus after he runs off to meet more humans. In the True Pacifist Ending Credits, Undyne kisses Alphys on her left cheek and laughs when she faints in embarrassment. She then punches the sidewalk beside her while laughing, causing it to crack.

Genocide Route

You're gonna have to try a little harder than THAT.

Undyne the Undying

After the protagonist attacks the Monster Kid, Undyne protects them and takes the blow instead. Even though her HP reduces to zero, Undyne holds on through Determination and reforms into Undyne the Undying.[13] If the protagonist defeats her, she tells them that Alphys was watching their battle and has evacuated the rest of the monsters to safety.[14] Undyne begins melting due to her Determination and then turns to dust.

In Battle

For an in-battle description, see Undyne/In Battle.



Alphys and Undyne love one another. Undyne first met Alphys in the Garbage Dump, listening for hours about where she thought the abyss there led. The two became close friends soon after, with Alphys introducing her to anime at some point, although Alphys told her that they were history biopics about humans. They hang out often, and Alphys uses the seagrass throughout Waterfall to make a special frosty treat for Undyne.[15] Alphys and Undyne also worked together to create some of the puzzles in Waterfall.[16] At some point Undyne fell in love with Alphys due to her confidence in what she liked and her work but didn't know how to express this. She apparently called her once just to ask her what the weather was like, even though the Underground has no weather. She would also constantly write letters expressing her feelings but she'd always change her mind when she went to deliver them and go back to write another one.[17]

She quit her job as head of the Royal Guard at the end of the Family Ending to be Alphys's lab assistant, where she apparently caused a lot of explosions.[18]

In the True Pacifist Route, Undyne calls the protagonist to have them deliver one of her letters to Alphys but quickly changes her mind after changing into some casual clothes. She discovers them in the dump, having a pretend date due to Alphys thinking the letter was from the protagonist, where she hears Alphys saying she loves her. This leads to a conversation where Alphys confesses everything to her, which she mostly accepts, but she starts freaking out after Alphys leaves about the idea that anime is not real. She asks the protagonist if it is true, and if they confirm that it is, she becomes devastated but decides to put up a brave face for Alphys's sake. They nearly kiss while visiting the protagonist after the Asgore fight is interrupted, but Toriel interrupts them and tells them not to kiss in front of the protagonist. Undyne is seen kissing Alphys on the cheek on the beach during the credits and laughs when the latter faints.


Undyne thinks of Papyrus as a close friend. She is impressed by his persistence, but is concerned about his well-being and secretly does not want him to join the Royal Guard because she believes he is too kind to even fight.[19] As a result, she teaches him how to cook in hopes for him to defer from joining. Undyne sometimes enjoys messing with Papyrus,[20] but she often forgets that he usually takes things literally.[21] She becomes heartbroken and infuriated if the protagonist kills Papyrus during a Neutral/Genocide Route.

The Protagonist

Undyne initially despises the protagonist and believes that they would be more useful dead than alive.[22] If the protagonist spares her and offers her water in Hotland, she begrudgingly befriends them if they have earned no EXP. Though Papyrus tricks Undyne into befriending the protagonist, she genuinely cares about them at the end of their hangout. However, if the protagonist betrays her by killing monsters after her hangout, she ends up hating them more than she would if they did not hang out with her at all.[23][24]

If the protagonist earned no EXP and befriended Undyne in a previous playthrough, she remembers them vaguely as a friend but brushes off the feeling before her battle.[25]


Even though Asgore is her boss, Undyne sees him as a friend and knows his favorite type of tea. When she was younger, Undyne challenged Asgore to a fight but could not land a single blow on him.[26] She was humiliated because he did not fight back and only dodged her attacks. Asgore then offered to train Undyne and eventually promoted her to head of the Royal Guard.

After Toriel refuses to "be friends again" with Asgore in the True Pacifist Route, Undyne sympathizes with him.[27]


Napstablook and Undyne live in the same neighborhood, and Napstablook is intimidated by her.[28] She still tries to be a good neighbor to them. She seems concerned about them being alone after their cousin left and tells the protagonist to be nice to them.[29]


Undyne does not know that Mettaton is Napstablook's cousin. She has a distaste for him,[30] and she does not like his show.[31] Though she does acknowledge that she "admires his lifestyle."[30]


Undyne used to give piano lessons to Shyren,[32] but one day she stopped coming – presumably after her sister fell down.

Monster Kid

Undyne appears to care for Monster Kid's safety. This can be seen when Undyne saves them after they fall off a cliff. This aspect appears more prominently in Genocide Route, where Undyne takes a fatal blow in their place.



  • "Undyne" derives from "Undine," a womanly water nymph from Greek lore. It is also a play on "undying," as Undyne does not die when reduced to zero health.
    • When attempting to name the fallen human "Undyne," the response becomes "Get your OWN name!" and prevents the name from being used.
  • Undyne is consistently shown to be right-handed. However, after scoping the protagonist after Papyrus's report, she handles her spear in her left hand.
  • Undyne's presence causes the sound of rushing water (stored in mus_ambientwater.ogg) to slow down by 10% in two cases:
    • After the floating tile, before the spear throwing part starts. (the next time the water can be heard, it's back to normal)
    • After the scene where Undyne drags the Monster Kid off-screen. (loading a save or re-entering the area reverts this to normal)
  • When Undyne was younger, she followed Gerson around to watch him beat up bad guys, much like how Monster Kid follows Undyne. However, whenever Undyne tried to help Gerson fight bad guys, she ended up attacking "the mailman or something like that."[33]
  • If Undyne jumps off the cliff to save Monster Kid, her HP is lowered in the following battle.
    • According to Toby, he wanted her armor to be cracked too, but he forgot to add it.[34]
  • There is a glitch where if the protagonist is standing as far to the left as possible while initiating Undyne's monologue, they can be shot very high up. The protagonist can then enter the cave, effectively postponing the first fight.
    • If the battle is initiated normally at this point, the protagonist is still able to move in the air, but Undyne pursues them on a bridge similar to the one heading to the Art Club Room in Hotland.
  • If either Snowdrake, Shyren, or any or all of the members of the Snowdin Canine Unit are killed, Undyne comments on it on her pre-battle monologue.
    • Papyrus's death supersedes all other pre-battle dialogue and changes her speech the most.
  • If Papyrus is killed, Undyne's face appears in the dialogue box before her battle despite never taking off her helmet. If the protagonist approaches to fight Undyne, she appears without her helmet.
  • Undyne and Toriel are the only bosses that the protagonist can flee from during a battle on a Neutral Route.
    • However, Undyne's battle can only be fled from if the protagonist's SOUL is red.
  • Despite having an eye patch in her left eye, it is absent in Undyne's west-facing sprites.
  • When Undyne says "En Guarde!" before her fight with the protagonist begins, the sentence is misspelled. The right spelling is "en garde," as the sentence is in French. This could also be a combination of the French and English spelling, Garde, and Guard, giving Guarde.
  • Undyne is the only character to use attacks whose colors correspond to how they move instead of how they do damage. (they all do damage as if they were white) All of her Green Mode spears are either white and blue or yellow. Also, her spear she throws when doing a green to red switch is white and blue and has a shadow.
  • While in Undyne's house for the befriending scene, the table that the protagonist sits at is decorated with a doily. The doily cracks along with the table after Undyne throws a spear at it.
  • Undyne tells the protagonist, when they try to interact with the door to her room, that no nerds are allowed. Then, she says that some nerds are, possibly referring to Alphys.
  • Undyne claims to dislike soda, despite owning a bottle herself. However, Alphys owns a cup with some soda in it. It's possible that Undyne keeps it for when Alphys comes over.
  • In Undyne's faux battle, she has one more DF than in her actual battle, despite being unarmored.
  • Due to her "research," she references a lot of anime and anime cliches without realizing it.
    • When in battle her armor is very similar to the Battle Armor from the Dragon Ball series.
    • She has a giant sword in her house, stating that the humans she researched had swords up to ten times their size. This in reference to shows, like Bleach and Berserk, where characters can have comically large swords.
    • When calling Undyne in front of the Royal Guards blocking the way to the elevator, she admits she is unable to help because she told them already to disregard her orders if it were to help a human as she found out that, after "researching" with a specific animation, humans could control minds during wartime. Undyne also mentions the animation is 'really good', making the talk a possible reference to Code Geass for its similar premise and critical acclaim.
  • Undyne has the most crude vocabulary of any characters in the game due to her hot-blooded and aggressive personality. While she is capable of using polite replacements like "darnit", most of the actual mild expletives said in the game come from her.
  • When the protagonist calls Undyne in the grass room where she almost grabbed them, Undyne comes close to using stronger language during the call.[35]
  • Undyne the Undying is the only boss in the Genocide Route that cannot be defeated in 1 hit.
  • Undyne is the only character who has a boss fight in all 3 routes.

See Also


  1. how is undyne's name pronounced? - undertale on Tumblr, October 06, 2015.
  3. I don't actually want to hurt you either. At first, I hated your stupid saccharine schtick, but... The way you hit me right now, it... Reminded me of someone I used to train with. - Undyne
  5. I've READ Alphys's human history book collection! I know all about your giant swords... Your colossal, alien-fighting robots... Your supernatural princesses... - Undyne
  6. That's where I first talked to you! Weren't you SUPER terrified? I practice that monologue ALL the time in the mirror! - Undyne
  7. Going off-the-cuff... It helped that I... Uh. Completely forgot the words to my monologue, anyway... - Undyne
  8. Why would I EVER be friends with YOU!? If you weren't my houseguest, I'd beat you up right now! - Undyne
  9. Oh My God? Did YOU write this letter? It wasn't signed, so, I had no idea who could have... - Alphys
  10. NGAHHHH!!! NGAHHH!!!! I'M UNDYNE AND I'M PILING ON THE SMOOCHES!!! - Alphys roleplaying as Undyne
  11. What I like about you is that you're PASSIONATE! You're ANALYTICAL!! It doesn't matter what it is! YOU CARE ABOUT IT!! - Undyne
  12. Alphys... I want to help you become happy with who you are! - Undyne
  13. Deep, deep in my soul. There's a burning feeling I can't describe. A burning feeling that WON'T let me die. - Undyne
  14. Alphys told me that she would watch me fight you... And if anything went wrong, she would... evacuate everyone. - Undyne
  15. Ugh, ice cream!? Sugary... COLD... Talk about GROSS. Now this chilly pink stuff that Alphys makes me... - Undyne
  16. Alphys helped measure out the mud tiles for this puzzle. It was a lot of work, but we got to make sand castles after. - Undyne
  19. But, um, to be honest... ...I don't know if I can ever let Papyrus into the Royal Guard. Don't tell him I said that! He's just... well... I mean it's not that he's weak. He's actually pretty freaking tough! It's just that... he's... he's too innocent and nice!!! I mean, look, he was SUPPOSED to capture you... and he ended up being friends with you instead! I could NEVER send him to battle! He'd get ripped into little smiling shreds. - Undyne
  21. Papyrus, wait, you know I'm joking, right...? - Undyne
  22. You know what would be more valuable to everyone? IF YOU WERE DEAD!!! - Undyne
  24. SHE STILL BLAMES YOU... FOR THE DISAPPEARANCE OF ASGORE. - Papyrus, if Undyne was not befriended.
  25. The whole time I was chasing after you... I felt something... Strange. The echoes of something warm, something... Something like "I miss being friends with you." - Undyne
  26. Y'know, I was a pretty hotheaded kid. Once, to prove I was the strongest, I tried to fight ASGORE. Emphasis on TRIED. I couldn't land a single blow on him! - Undyne
  27. Hey ASGORE, is that your ex? Jeez. That's rough, buddy. - Undyne
  28. hmmm... i should probably try to make friends with my neighbor. she's kind of scary, but i feel like i'm always too late to make friends... - Napstablook
  29. Be nice to them, okay!? Cherish this ghost!!! - Undyne
  30. 30.0 30.1 All he did was lie seductively on the piano... And fed himself grapes. I don't really like that guy. But I admire his lifestyle. - Undyne
  32. Oh yeah, Shyren lives around here. I used to give her piano lessons. - Undyne
  33. When she was younger, Undyne would follow me around, to watch me beat up bad guys... Sometimes she'd even try to help! Though, most of the time the folks she attacked weren't bad guys. It'd be the mailman or something like that. - Gerson
  34. If Undyne jumps off the cliff to save Monster Kid, when you fight her, her HP's lowered. I wanted to have her armor cracked too but I forgot - Toby Fox (@tobyfox) on Twitter, June 13, 2016. Archived on August 29, 2017.
  35. If it wasn't for that grass I'd have kicked your... Uh, if not for that grooty I'd have kicked your booty. Don't ask me what a grooty is!!! - Undyne