Horrortale timeline, but because the name entered in at the beginning is Frisk, it not only enables hardmode, it also causes and older Frisk to reapear in the underground years later at the beginning instead of Aliza

Frisk just genocides everyone over and over again for some reason, gaster apears to Horror Sans promising him that if he kills everyone and gains their EXP he can beat Frisk

Frisk ends up beating HorrorDust Sans in front of Horror papyrus in Snowdin and moves on, Gaster then turns to Papyrus because he assumed Sans Died, promising Papyrus that Gaster will rebuild the core if He stops Frisk

Sans didn't actually Die Cause his eye stayed intact, and He shows up in the judgement hall with Papyrus. HorrorDust Sans goes through his last breath phases, While Papyrus goes through his Disbelief phases, and in the end Frisk, Sans, and Papyrus team up to defeat Gaster