Shara was beaten by the killer demons, so she decided to become the new killer demons in this world, and finally eliminated all killer demons and other allies to gain more power, until pusaster was go missing, so he went off to find the killer demons, and the big m town was burned and killed by shara, leaving her encounter and kills the population, but pusaster was the only hero alive to stop her.

DustRemixerNightmare by @GoreyMonster69

Dusttale by Ask-Dusttale

Undertale by Toby Fox.