4 parts Complete There are 3 alternate timelines of the original Classic Sans, with each of them become extremely powerful under very unique circumstances.
There is Geno Sans, who had injected DT into his own soul, and had died, forcing him to reside inside of the Save Screen, in order to stay alive in this place.
There is Color Sans, who had absorbed the 6 human souls in order to become more powerful than ever before, but was erased from existence when he killed the human, and went into the void, being forgotten by everyone that knew that he once existed.
There is Seraphim, who had acted fast and quickly killed the human, who's name is Frisk, before they went to the king and was controlled to start their genocide, and absorbed all 7 human souls, become the most powerful monster of infinite power amongst his kind, before he had been teleported to the void by the souls when Alphys tried to remove them, which nearly killed him.
All 3 of them are versions of Classic Sans that went to a void, or a place similar to the void, in the case of Geno Sans, in order to survive. But what happens when these 3 extremely powerful versions of Sans meet, when they go into a version of Judgement Hall?