"look, i don't have to take orders from a child."
"Actually, you're legally required to. Mom said so."
-- UF!Sans and SS!Asriel
MashTale is an UnderTale AU created through the creative laziness by User:Aidanthehedgehogisawesome.
"Once upon a time, there were two races who ruled the goddamn world like BADASSES." -- Narrator Chara
After the events of Undertale, Frisk [RESET] and attempted a second Pacifist route. However, in that universe, they didn't care as much as the first time. They allowed themselves to make mistakes and be a klutz, which, in the ASRIEL battle, cost them their SOUL. ASRIEL used it to [RESET] the world, but....
...Something went wrong.
ASRIEL was unable to control the DETERMINATION, which caused a large explosion in the multiverse. The bubbles of the Whole World popped one by one, and everything spilled out. In retaliation, the Whole World sealed it all together.
As the worlds merged, so did the characters at a molecular level, and thus 'poofed' into quantum particles within the Bubble. The Human later woke up within The Boulevard universe, and thus had to 'rebuild', or sorts. The universe they formed first was similar to that of Undershards, but it was unstable, and collapsed, sending the Human elsewhere. This left room for a new Human. Thus, the Humans began to take turns each [RESET], with each character being swapped every time by a randomized FUN value (1 to 1,000,000,000).
"Lol, you don't even have to make this section.
They're always randomized from other AUs; no matter what.
Well, by each [RESET], anyway."
-- 4th Wall!Flowey
As stated above, the characters are reassigned each [RESET]. In one play-through you could be doing Doctor Grape and chilling with StoryShift!Papyrus, but in the next you could be running the fuck away from Hunter!Grey whilst surviving constant attack from Nazi!Papyrus. The play style spins with each [RESET] as well, as a new Human is placed as the main character.
- The AU is canonically placed on the ending of each timeline.
- Undershards!Toriel is, no matter what, always present on the first play; as well as Emo!Sans and Captive!Papyrus.
- UnderLust is the least common AU to end up in.
- UnderHerTail is the second least.
- UnderFell is the most common.
- UnderTale: Yellow is the second most.