Spiro

in this undertale universe instead of Frisk falling the person names spiro falls down to the underground monsters before our frisk,he went through the monsters as a pacifist he actually stayed with the monsters instead of leaving, he became a monster and half human in that timeline because he's sacrificed himself and fused with all the monsters Underground and the Seven Souls including gaster and Chara because he stop player from genocide when he defeated the player he reset the timeline