Undertale Wiki

Aaron is an enemy that appears in Waterfall.



He is a brown, muscular merhorse (or rather a sea horse) with a long, winding green tail and a twelve-pack.


Aaron's lines are vaguely flirty as well as creepy, and he adds a winking face to the end of every line he speaks. He has a high obsession with flexing that, should the protagonist choose the "Flex" option, he takes it as a fun challenge.

In Battle

Appears With


  • Flexing muscular arms move upward from the right and left sides of the Bullet Board. They speed up as the seconds go by.
  • Sweat falls straight & diagonally from the top of the box.


  • To spare him, the protagonist must flex at Aaron. The first time, he takes it as a challenge to a flexing contest; the second time, he flexes harder; and the third time, he flexes so hard that he ends up leaving the room.
    • After each flex, the protagonist and Aaron have increased attack.
    • If Aaron appears due to flexing at a Temmie, he only requires one flex to leave.
  • If "Joke" is selected while fighting Aaron alongside Woshua, Aaron becomes spareable.
  • If the protagonist plays one of Napstablook's music CDs, Aaron and Woshua are encountered in the room with the SAVE Point in front of Napstablook's house. Instead of fighting, they are immediately scared off by how spooky the music is, unlocking the yellow text in the True Pacifist Ending Credits.
    • After this event, his encounter dialogue is different, and it is possible to make Aaron leave in battle by shooing him.


  • CHECK all you want! ; ) [Check]
  • I sure do love muscles ; ) [Neutral]
  • Education? Hobby? Talent? ; ) [Neutral]
  • Come on in, the water's fine ; ) [Neutral]
  • No need for a swimming suit ; ) [Neutral]
  • Whew, I'm sweating ; ) [Neutral]
  • Sure isn't creepy out ; ) [Neutral]
  • Flexing contest? Ok, flex more ; ) [Flex]
  • Nice!! I won't lose tho ; ) [Flex]
  • Ooh, I have to disagree ; ) | Just the two of us, huh? ; ) [Flex at Temmie]
  • Temmie, are you okay? ; ) | Hi? ; ) [Flex at Temmie after scary music encounter]
  • Wow! Spunky! Love it ; ) [Shoo]
  • Feisty, huh?? ; ) [Shoo]
  • You'll change your mind ; ) [Shoo]
  • Haha, nice. My kind of joke ; ) [Joke]
  • Don't get too close ; ) [Touch]
Napstablook's remix easter egg (with Woshua and Aaron)
If the protagonist turns on one of Napstablook's music and heads outside, they encounter Woshua and Aaron, and trigger this easter egg. After it is complete, shooing Aaron causes him to leave the battle.
  • [Woshua] ... what the HECK is that music?
  • [Woshua] ... this is worse than Shyren.
  • [Aaron] No way, Shyren is way less scary ; )
  • [Woshua] ... if you're so scared, why do you keep winking?
  • [Woshua] Forget it. This beat is too... ... filthy.
  • [Aaron onward] Wosh! Wait! Don't leave me ; )
  • Is this creepy music my punishment for being creepy? ; )
  • Please... stop... I'll never creep again ; )
  • Wahhhhh!!!!! ; )

Flavor Text

  • Aaron flexes in! [Encounter]
  • Woshua and Aaron appear. [Encounter with Woshua]
  • You shouldn't read this. [Unused, intended for the scary music encounter]
  • This seahorse has a lot of HP (Horsepower). All of his attacks are harder to dodge at the bottom of the box. [Check]
  • Aaron is admiring his own muscles. [Neutral]
  • Smells like a mussel farm. [Neutral]
  • Smells like an underwater barnyard. [Neutral]
  • Aaron is splashing you playfully. [Neutral]
  • Aaron is sweating bullets. Literally. [Neutral]
  • You tell Aaron to go away. [Shoo]
  • You tell Aaron to go away. He agrees. [Shoo after having flexed or after scary music encounter.]
  • You flex. Aaron flexes twice as hard. ATTACK increases for you two. [Flex #1]
  • You flex harder. Aaron flexes thrice as hard. ATTACK increases for you two. [Flex #2]
  • You flex. Aaron flexes very hard... He flexes himself out of the room! [Flex #3]
  • Aaron is ready for your next flex. [Neutral after Flex]
  • Aaron's muscles droop comically. [Low HP]
  • Aaron is looking around, fearful of something. [Neutral after scary music encounter]


  • Aaron is named after and slightly based on a former roommate of Toby Fox.
    • When "Aaron" is typed for the first human's name, the response becomes "Is this name correct? ; )"
  • A parallel seems to have been drawn between Aaron and an enemy from the SNES game Breath of Fire II called Dir. HR which is also very muscular and shirtless. When it attacks, it says "Education? Hobby? Talent!?" and then performs a flexing animation.
  • Additionally, Toby is aware of the Homestuck connection to this enemy.
  • Aaron's hurt sprite is used by most monsters as their default sprite. If monsters that can't normally be spared without hacking the game are spared, their spared sprite appear as Aaron's hurt sprite.
    • Prior to v1.001, upon killing Ice, their vaporization looks like Aaron's hurt sprite[1]
  • Aaron does not appear to tell the story of Asriel Dreemurr in New Home, possibly because he ends all his sentences in winks, which would have distorted the content.
  • Aaron is hated by all Temmies because of his constant flexing, and he is attracted by such acts. This would explain why flexing at a Temmie causes him to appear.
  • Aaron has an apparent dislike for music. He may, however, just dislike Napstablook's tunes and Shyren's singing,[2] specifically.
  • Aaron is one of the monster species making up the Amalgamate Lemon Bread; specifically, Lemon Bread is spared by flexing, an ACT adopted specifically from Aaron, and Lemon Bread appears to have Aaron's bicep attached to its body and the ends of Aaron's tails for eyes. She also confirms this at the end of a True Pacifist Route, where she comments that her other parts do not look forward to seeing Aaron.
  • Aaron is one of the few monsters who rewards more GOLD when spared than when killed.


  1. Killing 'Ice' in Undertale. - YouTube
  2. You smile. You ask to see Shyren's smile, too. Shyren gets quieter. In the corner, Aaron nods his head approvingly. - Flavor text in Shyren's battle