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Underfoil is a Sub-AU of EntropyTale that is in concept similar to Underfell, in that the characters are much more evil than their original counterparts. However, Underfoil is more of a complete opposite than simply corruption, with the exception of a few things being taken out or added. After Asriel killed Chara and took their SOUL to the surface, only to underestimate the humans and die, Toriel wanted vengeance, and to go to the surface to kill humans. However, Asgore decided to honor Chara's wishes and didn't instate a policy to kill all humans. Toriel is furious upon this, and runs away to the Ruins to kill humans and overthrow Asgore.


Partially the same as Undertale, except the events that happen in Pacifist happen in Genocide, and the events that happen in Genocide happen in Pacifist, with a few exceptions and additions to both. As a general rule, the plot is the polar opposite of Undertale regarding the monsters' alignments and views.



An innocent creature who urges Frisk not to kill anyone. He is very optimistic and believes that every monster can be good. His catchphrase is, "In this world, it's love and be LOVEd!" He is fried to a crisp when Toriel enters the first room, but of course comes back later as usual. In Genocide, after the Asgore fight is over, Flowey takes the six SOULs and attacks Frisk, sad, disappointed, and angry that Frisk decided to kill everyone. Once Flowey is defeated, Asriel appears out of the Six SOULs and acts similar to Chara at the end of Genocide, with the inevitable options being ERASE and Do Not, and a similar outcome. Themes: "ymenE tsroW ruoY", "evoL dna ,elimS ,maerD ,epoH".


The malevolent ex-wife of Asgore who vehemently hates humans. Residing in the RUINs, she attempts to capture any she spots. Theme: "kaerbtraeH". Check: "Doesn't know worst for you."


An evil but self-controlled skeleton who lives in Snowdin. In the Pacifist Route, he condemns the protagonist for not putting them out of their misery, and attacks them. Sans' pupils never appear, excluding his purple and green flashing eyes in the Pacifist Route. Theme: "ainavolroniM". Check: "The hardest ally. Can't only deal -1 damage."


A very evil skeleton who uses dirty traps, abandoning his more pathetic ones. In Genocide, he comments that he appreciates the protagonist's distaste for such harmless traps when they walk through. Theme: "dnirgenoB". Check: "He dislikes likes to say, 'heH heH heyN!'"


A fish monster who, in the Pacifist Route, hunts the protagonist, and is the Royal Executioner- the name for the Head of the Royal Guard. Once Frisk has successfully pacified Monster Kid and taught him how to be kind, Undyne kills him (unless he is shoved out of the way beforehand) and attacks. When the protagonist refuses to attack Undyne, she becomes Undyne the Loathsome and becomes a very difficult boss. Themes: "noitpurroC fo raepS", "nialliV eurT a tsniagA elttaB". Check: "The villain that ALWAYS gives up." "Villain forged from her own DIFFIDENCE to destroy earth."


A diabolical Royal Scientist working for Asgore. She captured Napstablook, the cousin of Mettaton, and held him hostage, demanding that Mettaton be a slave to her in the body she made for him. Unlike Undertale, she has a battle, but doesn't attack, unless during Pacifist. She eventually gets angry and attacks a few times, until Mettaton stops her, giving Frisk a chance to spare Alphys. If Alphys is spared, she kills Napstablook, much to the dismay of Mettaton. In Genocide, she dies in one hit. Theme: "rehsurC epoH".


A ghost in a robot body that Alphys called Mettaton. He betrays Alphys during her battle, giving Frisk a chance to attack Alphys. If spared, Mettaton is furious, and his betrayal of Alphys causes the death of Napstablook. In this situation, he is in the CORE. During his Pacifist battle, he uses his Mettaton DOOM form. He dies in one hit in this form, though causing a Neutral Route. In Genocide, he becomes Mettaton SLAV, a form created by Alphys for her own pleasure, during which Mettaton uses his combat features that were also added for "kinks". Themes: "riapseD yb htaeD", "MOOD fo htarW". Check: "His strongsuit isn't his shattered SOUL." "Alphys' least pathetic invention."


A spider monster whom Asgore, Alphys, and Undyne locked in her parlor for fun. Luckily for Muffet, she could eat her spiders and drink their blood, but she knew that she needed to do so sparingly, due to the fact that, if it was only her in there without any spiders, the webs would quickly collapse. Now, she eats her spiders as sparingly as she can, running out after years trapped. Muffet has forgotten about her past hatred and bake sale in which she lured customers in and trapped in webs for later consumption. Now, all she wants is freedom, more food, and a human SOUL so she could get revenge on her captors who only laughed at her sorrow.


A sad King who regrets his decision not to listen to his wife and kill humans. During Genocide, he attacks. During Pacifist, he can simply be spared. Theme: "niatnuoM eht rednU rotatciD". Check: " . . . "


A loving human who was taken advantage of by the Dreemurr family long ago. At the end of the Pacifist Route, despite their previous bad experiences with monsters, thanks Frisk for their kindness. During Genocide, Chara does not appear.


Gaster was the former Royal Scientist who built the CORE. His alignment is relative; if the reader's view of Undertale Gaster is that he was good, then he is evil. If the reader's view of Undertale Gaster is that he was evil, then he is good. If your view of him was neutral, then he is neutral (but the good and bad things about him are switched.)

Seven SOULs -

  1. Yellow - Corruption.
  2. Blue - Shame.
  3. Aqua - Intolerance.
  4. Green - Cruelty.
  5. Orange - Fear.
  6. Purple - Apathy.
  7. Red - Spite.


  • The overworld sprites' colors are mostly either inverted from the original sprites or darkened. Everything else is small and tacked on as extra.
  • The color of the SOULs are not inverted, however, only their representations, with the exception of the Red SOUL, who's representation is it's Undertale counterpart's vice to it's representation.
  • The eyes of the characters are often the brightest part of their sprite, and are usually either kept the same color or lightened slightly from the original sprites.
  • All of Underfoil's soundtrack is Undertale's soundtrack, played backwards.
  • Peculiarly, the checks on the characters are often less representative of their characters in Underfoil rather than a nearly direct opposite to Undertale's descriptions, whether accurate or not.



Underfoil Battle Sprites, Pacifist on top, Genocide on the bottom, in order of battle and/or meeting.