*Have you thought about a world where everything is exactly the same...
*Except you don't exist?

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* Do you wanna have a bad time?

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UnderMoon is the main story of Undertale, but during each of the changing moons, the characters change personalities. During the New Moon, Sans becomes an open and harmless character. Also during the New Moon, King Asgore becomes helpful and willing to support Frisk. During the Full Moon, Papyrus becomes very deadly and easily upset, and also during the Full Moon, Mettaton becomes murderous and self conscious. During the Waning Gibbous Alphys becomes outgoing and reckless. During the Waxing Gibbous Undyne becomes quite and deceiving. And during the 1st Quarter Moon, Toriel becomes resentful and hateful toward Frisk and any other child that fell into the Underground. Also there is one thing different involving Napstablook and Mettaton, these two characters are actually the spirits of dead humans who have fallen into the underground many years ago.


When the ground above Ebott had turned clear from a curse the human race had put on the monsters of the underground. After one of their own, Chara was "killed" by the monsters. Each monster was gifted with a curse to change their personalities during a certain time under the moon. There was no explanation what the real cause of this was other than speculations and rumors. When a human named Frisk falls into this madness, it is up to them to break the curse and restore what has been lost by resurrecting Chara.

Character Changes

Main Characters Affected By Moons

  • Sans - emotionally open and harmless during New Moon
  • Papyrus - becomes deadly and easily upset during Full Moon
  • Toriel - becomes resentful and hateful toward Frisk during 1st Quarter Moon
  • Undyne - becomes quiet and deceiving during Waxing Gibbous
  • Alphys - becomes outgoing and reckless during Waning Gibbous
  • Asgore - becomes helpful and willing to help Frisk during New Moon
  • Mettaton - becomes murderous and self conscious during Full Moon

Main Characters NOT Affected By Moons

  • Flowey
  • Frisk
  • Chara
  • Napstablook