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Underground is a (discontinued) Undertale AU created by AmericanTrailMix where all character's personalities are reversed, while keeping their interests and roles mostly intact. Some story elements are changed, and all non-important enemies are changed completely.



  • The yellow soul now fires fully automatically, and has to fight like a traditional shmup.
  • There is now a playable cyan soul, that is similar to the blue soul but can double jump.
  • There is also a playable orange soul, that can teleport to the opposite side of the battle box by pressing Z.
  • The purple soul is now altered so that the player is locked to a 3x3 grid of movement.
  • The Worn Dagger is now the Old Razor and the Heart Locket is now the Pocket Watch.
  • KR is replaced with KJ, which builds up during the players turn or when hit and decays during the opponent's turn. If full, it heavily damages the player; however, it can never kill them.


  • Flowey now acts friendly towards the player, and attempts to teach them how to survive in the Underground. It has been revealed by AmericanTrailMix that Flowey is actually Toriel, not Asriel.
  • Asriel is well and alive. No other information is known about them otherwise.
  • Frisk and Chara's names and shirts have been swapped.
  • Sans is now a dedicated, outgoing character named Roman, who accompanies Chara through Anville. He speaks in Times New Roman.
  • Papyrus is now a depressed, quiet character named Impact who wants to kill the protagonist for their soul, for several reasons. He speaks in Impact, and is the first boss of the Genocide route.
  • Undyne is now a calm, simple monster who follows the human around and does things for other monsters. She assumes the role of Sans as the one who meets you at the Judgement Hall and lectures you on LV. She is the final boss of the genocide route, and fights you with all seven soul types.
  • Alphys is a confident, bold personality, and has weaponized the amalgamations and treats them like pets. She understands that she has made mistakes, but believes that they were worth it in the name of science.
  • Mettaton was originally built as a human eradication robot, but became unstable and fled due to the uncooperative soul inside of him. He does not have an EX form, and skips straight to NEO. His genocide form is altered, but it is unknown how. He is the third boss of the Genocide Route.
  • Asgore is aggressive and irrational, and wants the human souls for the godlike power that he could use to possibly bring Toriel back from the dead.
  • W. D. Gaster has no influence or appearance in the story, though Impact posesses gasterblaster-like weapons.


  • The Ruins are now The Garden.
  • Snowdin is now the Ashen Forest, and Snowdin Town is now Anville, a blacksmithing town.
  • Grillby's is now Grillsy's, a family diner.
  • Waterfall is now Risen Falls, a fall-themed location.
  • Hotland is now Glacia, a massive computer and cooling system.
  • The CORE is now the MANTLE, a massive magithermal generator.
  • New Home is now Dark Place.

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